CHAPTER XXVIII

BRANCH CHORDATA (_Continued_). CLASS MAMMALIA:

THE MAMMALS

THE MOUSE (_Mus musculus_)

TECHNICAL NOTE.--It is best to catch specimens alive in a good trap.

A live trap well baited and placed in some old granary should

furnish plenty for class use. White mice can often be obtained at

"bird-stores." When mice are not procurable, use rats. A rat is

perhaps preferable on account of its size, but all essential

structures can readily be made out in the mouse. Specimens should be

killed by chloroform as described for the toad, p. 5.

=Structure= (fig. 147).--Compare the external characters of the mouse

with those of the toad and sparrow. The mouse, unlike the other

vertebrates so far studied, is thickly covered with _hair_ all over its

body except on the tip of the nose and the soles of the feet. Where are

the _nostrils_ placed? What are the large leaf-like expansions called

_pinnæ_ situated just back of the eyes? Pull open the _mouth_ and note

the large _incisor teeth_ on the upper and lower jaws. Cut one corner of

the mouth back and observe the large flat-topped _molar teeth_ on both

jaws. How does the attachment of the large fleshy _tongue_ differ from

the condition in the toad? The toad's tongue is for snapping up insects,

whereas in the mouse this organ serves to move food about in the mouth.

On the tongue are numerous small _taste-papillæ_. Notice the long hairs,

"feelers," on each side of the nose. Note the similarity between the

front paws and our own hands; each has four fingers with a small

rudimentary thumb on the inner side of the paw. How does the hind foot

of the mouse differ from the foot of man? Posteriorly the body is

terminated by a long _tail_. At the root of the tail is a small

aperture, the _anus_, and just below, or ventral to it, is the opening

from the kidneys and reproductive organs.

TECHNICAL NOTE.--Place the mouse on its back in a dissecting-pan and

cut through the skin from anus to the lower jaw. Extend the legs,

pin down each foot and pin out the cut edges of the skin. Now

carefully cut forward through the body-wall from the anal region and

on through the breast-bones and ribs. Pin each side out.

Near the hindmost pair of _ribs_ note a sheet of muscles, the

_diaphragm_, which extends across the body-cavity, dividing it into an

anterior portion, the _thoracic cavity_, and a posterior, the _abdominal

cavity_. What are the most conspicuous organs in the thoracic cavity?

Leading anteriorly to the mouth-cavity is a long tube, the _trachea_,

composed of a series of cartilaginous parts of rings placed end to end.

Note at its anterior end the _glottis_ and _epiglottis_. Insert a

blowpipe into the glottis and inflate the _lungs_, which will fill all

the otherwise unfilled space in the thoracic cavity. The abdominal

cavity contains the _viscera_ suspended in a fold of the lining

membrane, as in the other vertebrates studied. Note lying against the

diaphragm a large, red, glandular structure, the _liver_. Separate the

two large lobes of the liver and expose the opalescent _gall-bladder_.

By passing a canula into this and ligaturing, the _cystic duct_ may be

injected. Beneath the liver is a large loop-shaped expansion of the

alimentary canal, the _stomach_. Arising from the right end of the

stomach is the narrow _duodenum_, which gradually merges into the very

much convoluted _small intestine_, or _ileum_, which is followed by the

_large intestine_, or _colon_, the last part of which is a straight

tube, the _rectum_. The small intestine occupies most of the space in

the peritoneal cavity. Within the loop of the pylorus will be found an

irregular pinkish mass of tissue, the _pancreas_. Beneath the stomach on

the left side of the body lies a very dark glandular mass not much

unlike the liver but altogether detached from it. This structure is the

_spleen_, a ductless gland.

Note dorsally of the trachea a long tube passing through the diaphragm

and connecting the mouth with the stomach. What is this tube? Note the

_Eustachian tubes_ extending from the mouth to the ears. The median

part of the roof of the mouth is the _palate_, hard in front, soft

behind. A pair of small bodies at the sides of the soft palate near

its hinder end are the _tonsils_. At the posterior angle of the lower

jaw are glandular bodies, the _sub-maxillary glands_, which lead by a

short _duct_ anteriorly to open on the floor of the mouth. On the

sides of the neck just below the ears are pink or yellowish bodies,

the _parotid glands_, opening anteriorly in the sides of the

mouth-cavity. These two sets of glands are collectively known as the

_salivary glands_, the function of which is to secrete the saliva.

Push apart the sub-maxillary glands and note below them overlying the

trachea on either side two dark-red lobes connected by a band of

tissue. These constitute the _thyroid gland_, another of the so-called

ductless glands. Within the thoracic cavity anterior to the heart note

a mass of pinkish tissue, the _thymus gland_. Observe the large

_masseter muscles_, which cover the jaws. What is their function? On

either side of the neck lies a large blood-vessel, the _external

jugular vein_, which collects blood from the head and carries it down

to the heart. Note the large _pectoral muscles_ which cover the breast

and extend out into the arms, and which are so strong and highly

developed in the sparrow. The head is supported by large muscles which

run down the back of the neck to the ribs. Others are attached to the

ribs, which they raise and lower. These movements, together with the

contraction of the diaphragm, cause the expansion and contraction of

the thoracic cavity whereby the lungs are regularly filled and

emptied. Note that the abdomen is covered by a double layer of

muscular tissue, the outer part made up of the _external oblique

muscles_, the inner by the _internal oblique muscles_.

[Illustration: FIG. 148.--Diagram of the circulation of the blood in a

mammal; _a_, auricles; _l_, lung; _lv_, liver; _p_, portal vein

bringing blood from the intestine; _v_, ventricles; the arrows show

the direction of the current; the shaded vessels carry venous blood,

the others arterial blood. (From Kingsley.)]

Examine the _heart_. How many _auricles_ has it? The _ventricles_ in the

mouse, as in the bird, are entirely separated, forming two complete

compartments, a _right_ and a _left ventricle_. The blood flowing from

the veins of the body is collected in the right auricle, thence it

passes into the right ventricle, whence it is conveyed to the lungs;

returning it flows through the left auricle into the left ventricle,

whence it is forced through the arteries of the body. For a study of the

circulatory system in mammals (fig. 148), a rat or a rabbit should be

injected by the teacher and an advanced text-book, as Parker's "Zootomy"

or Marshall and Hurst's "Practical Zoology," used as a guide. A sheep's

heart is very good to cut open for a class demonstration.

Make a drawing of the organs observed thus far in the dissection.

The _kidneys_ in the mouse are situated in the dorsal region next to

the backbone. They consist of two bean-shaped smooth glands. From them

a pair of ducts, the _ureters_, can be traced down to a median

thin-walled muscular sac, the _bladder_. The bladder opens to the

exterior of the body by means of a short tube, the _urethra_. Cut open

a kidney longitudinally and examine the cut surfaces.

The two egg-glands of the female mouse lie in the median portion of

the abdominal cavity, somewhat below the kidneys, and from the

vicinity of each runs an egg-tube. These tubes meet below the bladder,

and open to the exterior of the body through the aperture noted below

the anus. In the posterior parts of these tubes lie until birth the

developing embryos.

TECHNICAL NOTE.--For a study of the nervous system place the

specimen ventral side down and cut through the skull with the

bone-cutters or heavy scissors, exposing the brain and spinal cord.

Note the large _brain_ (fig. 149), composed of small _optic lobes_,

large _cerebrum_, _cerebellum_, and _medulla oblongata_, followed by

the long _spinal cord_. Note the nerves arising from the brain and

spinal cord.

[Illustration: FIG. 149.--Diagram of brains of vertebrates; _Olf. L._,

olfactory lobes; _Cbr._, cerebrum; _Md. Br._, midbrain (optic lobes);

_Cbl._, cerebellum; _Med. Ob._, medulla oblongata; _Sp. Cd._, spinal

cord. (From specimens.)]

For a careful dissection of the mammalian nervous system a larger

mammal, such as a cat or dog or rabbit, should be used. For guide use

a text-book such as, for the dog, Howell's "Dissection of the Dog";

for the cat, Reighard and Jennings' "Anatomy of the Cat"; and for the

rabbit, Parker's "Zootomy" or Marshall and Hurst's "Practical

Zoology." Make a good preparation of the brain and preserve it for

future use in some fluid like Fischer's fluid (see page 453).

TECHNICAL NOTE.--Prepare a well-cleaned skeleton by boiling a

specimen in a soap solution and thoroughly cleansing it (see p.

452).

Note the very compact _skeleton_ of the mouse. Note the closely sutured

_skull_. How many _cervical_ or _neck vertebræ_ are there? The _ribs_

are attached to the _thoracic vertebræ_. How many pairs of ribs? The

bony thorax supports the _shoulder-girdle_ and bones of the fore legs.

The thorax is followed by a series of ribless vertebræ, the _lumbar

vertebræ_, which in the posterior region of the body fuse with the

_pelvic girdle_ supporting the hind limbs. The body vertebræ are

succeeded by the very much smaller _caudal vertebræ_. Compare the

skeleton of the mouse with that of the bird; also with that of the toad.

For directions for a detailed study of the skeleton see in Parker's

"Zootomy" an account of the skeleton of the rabbit, pp. 263-286.

TECHNICAL NOTE.--For the study of the eye (fig. 150) the teacher

should obtain the eye of some large mammal, as the ox or sheep,

with which to make a class demonstration. The eye of a rabbit or

cat can of course be used. For an account of the vertebrate eye

see Parker and Haswell's "Text-book of Zoology," Vol. II. pp.

103-107. For a study of the ear use a bird or mammal, and see pp.

107-110 of the same book.

[Illustration: FIG. 150.--Diagram of vertebrate eye; _c_, choroid;

_i_, iris; _l_, lens; _n_, optic nerve; _r_, retina; _s_, sclerotic.

(From Kingsley.)]

=Life-history and habits.=--The house-mouse is not a native of North

America, but was introduced into this country from Europe, to which,

in turn, it came from Asia, its original habitat. The mouse came to

this country in the vessels of early explorers. Similarly the brown

and black rats, now so abundant all over North America, and members of

the same genus as the mouse, were introduced from Europe. Accompanying

man in his travels the mouse has spread from Asia until it is now to

be found over the whole world.

The habits of mice are well known; their fondness for living in our

homes and outbuildings makes them familiar acquaintances. Their food

is varied; they seem to thrive best, however, on a vegetable diet.

Grains and nuts are favorite foods. The house-cat is their greatest

enemy, but man takes advantage of their instinct to go into holes by

constructing traps with funnel or tunnel entrances which, baited with

cheese or other favorite food, are fatally attractive. In climbing,

mice are aided by the tail. Their strong hind legs enable them to

stand erect, and even to take several steps in this posture. They can

swim readily, although naturally they rarely take to water. Their

special senses are keen, the senses of hearing and taste being

unusually well developed. Their "singing," which has been the subject

of much discussion, seems to be actually a voluntary and normal

performance which, however, hardly deserves to be called singing, but

rather a slightly varied peeping or whistling.

The mouse is a prolific mammal, producing from four to six times a

year broods of from four to eight young. The mouse makes a cosy nest

of straw, bits of paper, feathers, wool or other soft materials, and

in this the young are born. The newly born mice are very small and are

blind and helpless. They are odd little creatures, being naked and

almost transparent. They grow rapidly, being covered with hair in a

week, although not opening their eyes for about two weeks. A day or

two after their eyes are open they begin to leave the nest, and hunt

for food for themselves.

OTHER MAMMALS

The mammals constitute the highest group of animals, including man,

the monkeys and apes, the quadrupeds, the bird-like bats and fish-like

seals and whales; in all about 2500 species. They are found everywhere

except on a few small South Sea islands. Only a few species, however,

have a world-wide distribution. The name Mammalia is derived from the

mammary or milk glands with which the females are provided and by the

secretion of which the young of this class, born free in all but a few

of the lowest forms, are nourished for some time after birth. In size

mammals range from the tiny pigmy-shrew and harvest mouse, which can

climb a stem of wheat, to the great sulphur-bottom whale of the

Pacific Ocean, which attains a length of a hundred feet and a weight

of many tons. Mammals differ from fishes and batrachians and agree

with reptiles and birds in never having external gills; they differ

from reptiles and agree with birds in being warm-blooded and in having

a heart with two distinct ventricles and a complete double

circulation; finally, they differ from both reptiles and birds in

having the skin more or less clothed with hair, the lungs freely

suspended in a thoracic cavity separated from the abdominal by a

muscular partition, the diaphragm, and in the possession by the

females of mammary glands. In economic uses to man mammals are the

most important of all animals. They furnish the greater portion of the

animal food of many human races, likewise a large amount of their

clothing. Horses, asses, oxen, camels, reindeer, elephants, and llamas

are beasts of burden and draught; swine, sheep, cattle, and goats

furnish flesh, and the two latter milk for food; the wool of sheep,

the furs of the carnivores, and the leather of cattle, horses, and

others are used for clothing, while the bones and horns of various

mammals serve various purposes.

[Illustration: FIG. 147.--Dissection of the Mouse, _Mus musculus_.]

=Body form and structure.=--The mammalian body varies greatly. Its

variety of form and general organization is explained by the facts

that, although most of the species live on the surface of the earth,

some are burrowers in the ground, some flyers in the air, and some

swimmers in the water. Mammals never have more than two pairs of

limbs; in most cases both pairs are well developed and adapted for

terrestrial progression. In the aerial bats the fore limbs are

modified into organs of flight; among the aquatic seals, sea-lions,

walruses, and whales both sets are modified to be swimming flippers or

paddles. In many of these aquatic forms the hind limbs are greatly

reduced or even completely wanting.

Most mammals are externally clothed with hair, which is a peculiarly

modified epidermal process. Each hair, usually cylindrical, is

composed of two parts, a central pith containing air, and an outer

more solid cortex; each hair rises from a short papilla sunk at the

bottom of a follicle lying in the true skin. In some mammals the hairs

assume the form of spines or "quills," as in the porcupine. The hairy

coat is virtually wanting in whales and is very sparse in certain

other forms, the elephant, for example, which has its skin greatly

thickened. The claws of beasts of prey, the hooves of the hoofed

mammals, and the outer horny sheaths of the hollow-horned ruminants

are all epidermal structures.

The bones of mammals are firmer than those of other vertebrates,

containing a larger proportion of salts of lime. Among the different

forms the spinal column varies largely in the number of vertebræ, this

variation being chiefly due to differences in length of tail. Apart

from the caudal vertebræ their usual number is about thirty. The

mammalian skull is very firm and rigid, all the bones composing it,

excepting the lower jaw, the tiny auditory ossicles, and the slender

bones of the hyoid arch, being immovably articulated together. The

correspondence between the bones of the two sets of limbs is very

apparent. The number of digits varies in different mammals, and also

in the fore and hind limbs of a single species. Among the Ungulates

the reduction in the number of digits is especially noticeable; the

forefoot of a pig has four digits, that of the cow two, and that of

the horse one. The two short "splint" bones in the horse are remnants

of lost digits. The teeth are important structures in mammals, being

used not only for tearing and masticating food, but as weapons of

offence and defence. A tooth consists of an inner soft pulp (in old

teeth the pulp may become converted into bone-like material)

surrounded by hard white dentine or ivory, which is covered by a thin

layer of enamel, the hardest tissue known in the animal body. A hard

cement sometimes covers as a thin layer the outer surface of the root,

and may also cover the enamel of the crown. The teeth in most forms

are of three groups: (_a_) the incisors, with sharp cutting edges and

simple roots, situated in the centre of the jaw; (_b_) the canines,

often conical and sharp-pointed, next to the incisors; (_c_) next the

molars, broad and flat-topped for grinding, and divided into premolars

and true molars. There is great variety in the character and

arrangement of these structures in mammals, their variations being

much used in classification. The number and arrangement of the teeth

is expressed by a dental formula, as, for example, in the case of man

2--2 1--1 2--2 3--3

_i_----, _c_----, _p_----, _m_---- = 32.

2--2 1--1 2--2 3--3

[Illustration: FIG. 151.--A group of Rocky Mountain sheep, or "big

horns," _Ovis canadensis_, including males, females and young.

(Photograph by E. Willis from specimens mounted by Prof. L. L. Dyche,

University of Kansas.)]

The mouth is bounded by fleshy lips. On the floor of the mouth is the

tongue, which bears the taste-buds or papillæ, the organs of taste.

The œsophagus is always a simple straight tube, but the stomach varies

greatly, being usually simple, but sometimes, as in the ruminants

and whales, divided into several distinct chambers. The intestine in

vegetarian mammals is very long, being in a cow twenty times the

length of the body. In the carnivores it is comparatively short--in a

tiger, for example, but two or three times the length of the body.

The blood of mammals is warm, having a temperature of from 35° C. to

40° C. (95° F. to 104° F.). It is red in color, owing to the

reddish-yellow, circular, non-nucleated blood-corpuscles. The

circulation is double, the heart being composed of two distinct

auricles and two distinct ventricles. Air is taken in through the

nostrils or mouth and carried through the windpipe (trachea) and a

pair of bronchi to the lungs, where it gives up its oxygen to the

blood, from which it takes up carbonic-acid gas in turn. At the upper

end of the trachea is the larynx or voice-box, consisting of several

cartilages attaching by one end to the vocal cords and by the other to

muscles. By the alteration of the relative position of these

cartilages the cords can be tightened or relaxed, brought together or

moved apart, as required to modulate the tone and volume of the voice.

The kidneys of mammals are more compact and definite in form than those

of other vertebrates. In all mammals except the Monotremes they

discharge their product through the paired ureters into a bladder,

whence the urine passes from the body by a single median urethra.

Mammary glands, secreting the milk by which the young are nourished

during the first period of their existence after birth, are present in

both sexes in all mammals, though usually functional in the female only.

[Illustration: FIG. 152.--A group of moose, _Alce americana_, showing

male, female, and young. (Photograph by E. Willis from specimens

mounted by Prof. L. L. Dyche, University of Kansas.)]

The nervous system and the organs of special sense reach their highest

development in the mammals. In them the brain is distinguished by its

large size, and by the special preponderance of the forebrain or

cerebral hemispheres over the mid- and hind-brain. Man's brain is

many times larger than that of all other known mammals of equal bulk

of body, and three times as large as that of the largest-brained ape.

In man and the higher mammals the surface of the forebrain is thrown

into many convolutions; among the lowest the surface is smooth. Of the

organs of special sense, those of touch consist of free nerve-endings

or minute tactile corpuscles in the skin. The tactile sense is

especially acute in certain regions, as the lips and end of the snout

in animals like hogs, the fingers in man, and the under surface of the

tail in certain monkeys. All the other sense-organs are situated on

the head. The organs of taste are certain so-called taste-buds located

in the mucous membrane covering certain papillæ on the surface of the

tongue. The organ of smell, absent only in certain whales, consists of

a ramification of the olfactory nerves over a moist mucous membrane in

the nose. The ears of mammals are more highly developed than those of

other vertebrates both in respect to the greater complexity of the

inner part and the size of the outer part. A large outer ear for

collecting the sound-waves is present in all but a few mammals. A

tympanic membrane separates it from the middle ear in which is a chain

of three tiny bones leading from the tympanum to the inner ear,

composed of the three semicircular canals and the spiral cochlea. The

eyes (fig. 150) have the structure characteristic of the vertebrate

eye, consisting of a movable eyeball composed of parts through which

the rays of light are admitted, regulated, and concentrated upon the

sensitive expansion, retina, of the optic nerve lining the posterior

part of the ball. The eye is protected by two movable lids. In almost

all mammals below the Primates there is a third lid, the nictitating

membrane. In some burrowing rodents and others the eye is quite

vestigial and even concealed beneath the skin.

=Development and life-history.=--All mammals except the Monotremes

give birth to free young. The two genera of Monotremes produce their

young from eggs hatched outside the body; _Tachyglossus_ lays one egg

which it carries in an external pouch, while _Ornithorhynchus_

deposits two eggs in its burrow. The embryo of other mammals develops

in the lower portion of the egg-tube, to the walls of which it is

intimately connected by a membrane called the placenta. (In the

kangaroos and opossums, Marsupialia, there is no placenta.) Through

this placenta blood-vessels extend from the body of the mother to the

embryo, the young developing mammal thus deriving its nourishment

directly from the parent.

The duration of gestation (embryonic or prenatal development in the

mother's body) varies from three weeks with the mouse, eight weeks with

the cat, nine months with the stag, to twenty months with the elephant.

Like the birds, the young of some mammals, the carnivores for example,

are helpless at birth, while those of others, as the hoofed mammals, are

very soon able to run about. But all are nourished for a longer or

shorter time by the milk secreted by the mammary gland of the mother.

=Habits, instinct, and reason.=--Despite the wonderful examples of

instinct and intelligence shown by many insects and by the other

vertebrates, especially the birds, it is among mammals that we find

the highest development of these qualities and of reason. In the wary

and patient hunting for prey by the carnivora, in the gregarious and

altruistic habits of the herding hoofed mammals, in the highly

developed and affectionate care of the young shown by most mammals,

and in the loyal friendship and self-sacrifice of dogs and horses in

their relations to man, we see the culmination among animals of the

development of the functions of the nervous system. In the

characteristics of intelligence and reason man of course stands

immensely superior to all other animals, but both intelligence and

reason are too often shown by many of the other mammals not to make us

aware that man's mental powers differ only in degree, not in kind,

from those of other animals.

Pure instinct is hereditary, and purely instinctive actions are common

to all the individuals of a species. Those actions which the individual

could not learn by teaching, imitation, or experience are instinctive.

The accurate pecking at food by chicks just hatched from an incubator is

purely instinctive. Purely instinctive also is the laying of eggs by a

butterfly on a certain species of plant which may have to be sought for

over wide acres, so that the caterpillars when hatched shall find

themselves on their own special food-plant. Yet the butterfly never ate

of this plant and will never see its young. Such elaborate instincts as

these have been developed from the simplest manifestations of sensation

and nervous function, just as the complex structures of the body have

been developed from simple structures (see Chapter XXIX).

The feeding and domestic habits and the whole general behavior of

animals are extremely interesting subjects of observation and study.

And such observation intelligently pursued will be of much value. The

point to be kept ever in mind is that all animal habits are connected

with certain conditions of life; that in every case there is an answer

to the question "why." This answer may not be found; in many cases it

is extremely difficult to get at, but often it is simple and obvious

and can be found by the veriest beginner.

=Classification.=--The mammals of North America represent eight orders.

Three additional mammalian orders, namely, the Monotremata, including

the extraordinary duck-bills (_Ornithorhynchus_) and a species of

_Tachyglossus_ in Australia and Tasmania; the Edentata, including the

sloths, armadillos, and ant-eaters found in tropical regions; and the

Sirenia, including the marine manatees and dugongs, are not represented

(except by a single manatee) in North America. In the following

paragraphs some of the more familiar mammals representing each of the

eight orders represented in North America are referred to.

=The opossums (Marsupialia).=--The opossum (_Didelphys virginiana_) is

the only North American representative of the order Marsupialia, the

other members of which are limited exclusively to Australia and

certain neighboring islands. The kangaroos are the best known of the

foreign marsupials. After birth the young are transferred to an

external pouch, the marsupium, on the ventral surface of the mother,

in which they are carried about and fed. The opossum lives in trees,

is about the size of a common cat, and has a dirty-yellowish woolly

fur. Its tail is long and scaly, like a rat's. Its food consists

chiefly of insects, although small reptiles, birds, and bird's eggs

are eaten. When ready to bear young the opossum makes a nest of dried

grass in the hollow of a tree, and produces about thirteen very small

(half an inch long) helpless creatures. These are then placed by the

mother in her pouch. Here they remain until two months or more after

birth. Probably all the North American opossums found from New York to

California and especially common in the Southern States belong to a

single species, but there is much variety among the individuals.

=The rodents or gnawers (Glires).=--The rabbits, porcupines, gophers,

chipmunks, beavers, squirrels, and rats and mice compose the largest

order among the mammals. They are called the rodents or gnawers

(Glires) because of their well-known gnawing powers and proclivities.

The special arrangement and character of the teeth are characteristic

of this order. There are no canines, a toothless space being left

between the incisors and molars on each side. There are only two

incisor teeth in each jaw (rarely four in the upper jaw), and these

teeth grow continuously and are kept sharp and of uniform length by

the gnawing on hard substances and the constant rubbing on each other.

The food of rodents is chiefly vegetable.

Of the hares and rabbits the cottontail (_Lepus nuttalii_) and the

common jack-rabbit (_L. campestris_) are the best known. The

cottontail is found all over the United States, but shows some

variation in the different regions. There are several species of

jack-rabbits, all limited to the plains and mountain regions west of

the Mississippi River. The food of rabbits is strictly vegetable,

consisting of succulent roots, branches, or leaves. Rabbits are very

prolific and yearly rear from three to six broods of from three to six

young each. There are two North American species of porcupines, an

Eastern one, _Erethizon dorsatus_, and a Western one, _E. epixanthus_.

The quills in both these species are short, being only an inch or two

in length, and are barbed. In some foreign porcupines they are a foot

long. They are loosely attached in the skin and may be readily pulled

out, but they cannot be shot out by the porcupine, as is popularly

told. The little guinea-pigs (_Cavia_), kept as pets, are South

American animals related to the porcupines.

The pocket gophers, of which there are several species mostly

inhabiting the central plains, are rodents found only in North

America. They all live underground, making extensive galleries and

feeding chiefly on bulbous roots. The mice and rats constitute a large

family of which the house-mice and rats, the various field-mice, the

wood-rat (_Neotoma pennsylvanica_) and the muskrat (_Fiber

zibethicus_) are familiar representatives. The common brown rat (_Mus

decumanus_) was introduced into this country from Europe about 1775,

and has now nearly wholly supplanted the black rat (_M. rattus_), also

a European species, introduced about 1544. The beaver (_Castor

canadensis_) is the largest rodent. It seems to be doomed to

extermination through the relentless hunting of it for its fur. The

woodchuck or ground-hog (_Arctomys monax_) is another familiar rodent

larger than most members of the order. The chipmunks and

ground-squirrels are commonly known rodents found all over the

country. They are the terrestrial members of the squirrel family, the

best known arboreal members of which are the red squirrel (_Sciurus

hudsonicus_), the fox-squirrel (_S. ludovicianus_), and the gray or

black squirrel (_S. carolinensis_). The little flying squirrel

(_Sciuropterus volans_) is abundant in the Eastern States.

=The shrews and moles (Insectivora).=--The shrews and moles are all

small carnivorous animals, which, because of their size, confine their

attacks chiefly to insects. The shrews are small and mouse-like; certain

kinds of them lead a semi-aquatic life. There are nearly a score of

species in North America. Of the moles, of which there are but few

species, the common mole (_Scalops aquaticus_) is well known, while the

star-nosed mole (_Condylura cristata_) is recognizable by the peculiar

rosette of about twenty cartilaginous rays at the tip of its snout.

Moles live underground and have the fore feet wide and shovel-like for

digging. The European hedgehogs are members of this order.

=The bats (Chiroptera).=--The bats (fig. 153), order Chiroptera,

differ from all other mammals in having the fore limbs modified for

flight by the elongation of the forearms and especially of four of the

fingers, all of which are connected by a thin leathery membrane which

includes also the hind feet and usually the tail. Bats are chiefly

nocturnal, hanging head downward by their hind claws in caves, hollow

trees, or dark rooms through the day. They feed chiefly on insects,

although some foreign kinds live on fruits. There are a dozen or more

species of bats in North America, the most abundant kinds in the

Eastern States being the little brown bat (_Myotis subulatus_), about

three inches long with small fox-like face, high slender ears, and a

uniform dull olive-brown color, and the red bat (_Lasiurus borealis_),

nearly four inches long, covered with long, silky, reddish-brown fur,

mostly white at tips of the hairs.

[Illustration: FIG. 153.--The hoary bat, _Lasiurus cinereus_.

(Photograph from life by J. O. Snyder.)]

=The dolphins, porpoises, and whales (Cete).=--The dolphins,

porpoises, and whales (Cete) compose an order of more or less

fish-like aquatic mammals, among which are the largest of living

animals. In all the posterior limbs are wanting, and the fore limbs

are developed as broad flattened paddles without distinct fingers or

nails. The tail ends in a broad horizontal fin or paddle. The Cete are

all predaceous, fish, pelagic crustaceans, and especially squids and

cuttlefishes forming their principal food. Most of the species are

gregarious, the individuals swimming together in "schools." The

dolphins and porpoises compose a family (Delphinidæ) including the

smaller and many of the most active and voracious of the Cete. The

whales compose two families, the sperm-whales (Physeteridæ) with

numerous teeth (in the lower jaw only) and the whalebone whales

(Balænidæ) without teeth, their place being taken in the upper jaw by

an array of parallel plates with fringed edges known as "whalebone."

The great sperm-whales or cachalots (_Physeter macrocephalus_) found

in southern oceans reach a length (males) of eighty feet, of which the

head forms nearly one-third. Of the whalebone whales, the

sulphur-bottom (_Balænoptera sulfurea_) of the Pacific Ocean, reaching

a length of nearly one hundred feet, is the largest, and hence the

largest of all living animals. The common large whale of the Eastern

coast and North Atlantic is the right whale (_Balæna glacialis_); a

near relative is the great bowhead (_B. mysticetus_) of the Arctic

seas, the most valuable of all whales to man. Whales are hunted for

their whalebone and the oil yielded by their fat or blubber. The story

of whale-fishing is an extremely interesting one, the great size and

strength of the "game" making the "fishing" a hazardous business.

[Illustration: FIG. 154.--Male elk or wapiti, _Cervus canadensis_.

(Photograph by E. Willis from specimen mounted by Prof. L. L. Dyche,

University of Kansas.)]

[Illustration: FIG. 155.--Antelope, male, female, and young,

_Antilocapra americana_. (Photograph by E. Willis from specimens

mounted by Prof. L. L. Dyche, University of Kansas.)]

=The hoofed mammals (Ungulata).=--The order Ungulata includes some of

the most familiar mammal forms. Most of the domestic animals, as the

horse, cow, hog, sheep, and goat, belong to this order, as well as the

familiar deer, antelope, and buffalo of our own land and the

elephant, rhinoceros, hippopotamus, giraffe, camel, zebra, etc.,

familiar in zoological gardens and menageries. The order is a large

one, its members being characterized by the presence of from one to

four hooves, which are the enlarged and thickened claws of the toes.

The Ungulates are all herbivorous, and have their molar teeth fitted

for grinding, the canines being absent or small. The order is divided

into the Perissodactyla or odd-toed forms, like the horse, zebra,

tapir, and rhinocerus, and the Artiodactyla or even-toed forms, like

the oxen, sheep, deer, camels, pigs, and hippopotami. The

Artiodactyls comprise two groups, the Ruminants and Non-ruminants. All

of the native Ungulata of our Northern States belong to the Ruminants,

so called because of their habit of chewing a cud. A ruminant first

presses its food into a ball, swallows it into a particular one of the

divisions of its four-chambered stomach, and later regurgitates it

into the mouth, thoroughly masticates it, and swallows it again, but

into another stomach-chamber. From this it passes through the other

two into the intestine.

The deer family (Cervidæ) comprises the familiar Virginia or red deer

(_Odocoileus americanus_) of the Eastern and Central States and the

white-tailed, black-tailed, and mule deers of the West, the

great-antlered elk or wapiti (_Cervus canadensis_) (fig. 154), the

great moose (_Alce americana_) (fig. 152), largest of the deer family,

and the American reindeer or caribou (_Rangifer caribou_). All species

of the Cervidæ have solid horns, more or less branched, which are shed

annually. Only the males (except with the reindeer) have horns. The

antelope (_Antilocapra americana_) (fig. 155) common on the Western

plains also sheds its horns, which, however, are not solid and do not

break off at the base as in the deer, but are composed of an inner

bony core and an outer horny sheath, the outer sheath only being shed.

The family Bovidæ includes the once abundant buffalo or bison (_Bison

bison_) (frontispiece), the big-horn or Rocky Mountain sheep (_Ovis

canadensis_) (fig. 151), and the strange pure-white Rocky Mountain

goat (_Oreamnos montanus_). The buffalo was once abundant on the

Western plains, travelling in enormous herds. But so relentlessly has

this fine animal been hunted for its skin and flesh that it is now

practically exterminated (fig. 156). A small herd is still to be found

in Yellowstone Park, and a few individuals live in parks and

zoological gardens. In all of the Bovidæ the horns are simple, hollow,

and permanent, each enclosing a bony core.

=The carnivorous mammals (Feræ).=--The order Feræ includes all those

mammals usually called the carnivora, such as the lions, tigers, cats,

wolves, dogs, bears, panthers, foxes, weasels, seals, etc. All of them

feed chiefly on animal substance and are predatory, pursuing and

killing their prey. They are mostly fur-covered and many are hunted

for their skin. They have never less than four toes, which are

provided with strong claws that are frequently more or less

retractile. The canine teeth are usually large, curved, and pointed.

[Illustration: FIG. 156.--A buffalo, _Bison bison_, killed for its

skin and tongue, on the plains of Western Kansas thirty years ago.

(Photograph by J. Lee Knight.)]

While most of the Feræ live on land, some are strictly aquatic. The true

seals, fur-seals, sea-lions, and walruses comprise the aquatic forms,

all being inhabitants of the ocean. The true seals, of which the common

harbor seal (_Phoca vitulina_) is our most familiar representative, have

the limbs so thoroughly modified for swimming that they are useless on

land. The fur-seals, sea-lions, and walruses use the hind legs to

scramble about on the rocks or beaches of the shore. The fur-seals

(fig. 157) live gregariously in great rookeries on the Pribilof or Fur

Seal Islands, and the Commander Islands in Bering Sea.

The bears are represented in our country by the widespread brown,

black, or cinnamon bear (_Ursus americanus_) and the huge grizzly bear

(_U. horribilis_) of the West. The great polar bear (_Thalarctos

maritimus_) lives in arctic regions. The otters, skunks, badgers,

wolverines, sables, minks, and weasels compose the family Mustelidæ,

which includes most of the valuable fur-bearing animals. Some of the

members of this family lead a semi-aquatic or even strictly aquatic

life and have webbed feet. The wolves, foxes, and dogs belong to the

family Canidæ. The coyote (_Canis latrans_), the gray wolf (_C.

nubilus_), and the red fox (_Vulpes pennsylvanicus_) are the most

familiar representatives of this family, in addition to the dog (_C.

familiaris_), which is closely allied to the wolf. "Most carnivorous

of the carnivora, formed to devour, with every offensive weapon

specialized to its utmost, the Felidæ, whether large or small, are,

relatively to their size, the fiercest, strongest, and most terrible

of beasts." The Felidæ or cat family includes the lions, tigers,

hyenas, leopards, jaguars, panthers, wildcats, and lynxes. In this

country the most formidable of the Felidæ is the American panther or

puma (_Felis concolor_). It reaches a length from nose to root of tail

of over four feet. Its tail is long. The wildcat (_Lynx rufus_) is

much smaller and has a short tail.

[Illustration: FIG. 157.--The Lukanin rookery of fur seals,

_Callorhinus alascanus_, on St. Paul Island, Pribilof Group, Bering

Sea. (Photograph from life by the Fur Seal Commission.)]

=The man-like mammals (Primates).=--The Primates, the highest order of

mammals, includes the lemurs, monkeys, baboons, apes, and men. Man

(_Homo sapiens_) is the only native representative of this order in

our country. All the races and kinds of men known, although really

showing much variety in appearance and body structure, are commonly

included in one species. The chief structural characteristics which

distinguish man from the other members of this order are the great

development of his brain and the non-opposability of his great toe.

Despite the similarity in general structure between him and the

anthropoid apes of the Old World, in particular the chimpanzee and

orang-outang, the disparity in size of brain is enormous.

[Illustration: FIG. 158.--"Bob Jordan," a monkey of the genus

_Cercopithecus_. (Photograph from life by D. S. Jordan.)]

The lowest Primates are the lemurs found in Madagascar, in which

island they include about one-half of all the mammalian species found

there. The brain is much less developed in the lemurs than in any of

the other monkeys. The monkeys and apes may be divided into two

groups, the lower, platyrrhine monkeys, found in the New World, and

the higher, catarrhine forms, limited to the Old World. The

platyrrhine monkeys have wide noses in which the nostrils are

separated by a broad septum and with the openings directed laterally.

These monkeys are mostly smaller and weaker than the Old World forms

and are always long-tailed, the tail being frequently prehensile. They

include the howling, squirrel, spider, and capuchin monkeys common in

the forests of tropical South America. The catarrhine monkeys have the

nose-septum narrow and the openings of the nostrils directed forwards,

and the tail is wanting in numerous members of the group. They include

the baboons, gorillas, orang-outangs, and chimpanzees. These apes have

a dentition approaching that of man, and in all ways are the animals

which most nearly resemble man in physical character.

PART III

ANIMAL ECOLOGY

CHAPTER XXIX

THE STRUGGLE FOR EXISTENCE, ADAPTATION,

AND SPECIES-FORMING

TECHNICAL NOTE.--Multiplication, or increase by geometric ratio,

among animals can be illustrated by noting the many eggs laid by a

single female moth or beetle or fly or mosquito or any other

common insect (or almost any other non-mammalian animal). The

production of many live young by each female rose aphid can be

readily seen; the number of young in a litter of kittens or pups

or rabbits is a good illustration. From this geometric increase it

is obvious that there must be a great crowding of animals and a

struggle among them for existence. This struggle and the downfall

of the many and success of the victorious few can be observed by

rearing in a small jar of water all the young of a single brood of

water-tigers (larva of _Dyticus_) or other aquatic predaceous

insect. The strongest young will live by killing and eating the

weaker of their own kind. In a spider's egg-sac the young after

hatching do not immediately leave the sac, but remain in it for

several days. During this time they live on each other, the

strongest feeding on the weaker. Thus out of many spiderlings

hatched in each sac comparatively few issue. This can be readily

observed. Open several egg-sacs and count the eggs in them. Let

the spiderlings hatch and issue from some other egg-sacs belonging

to the same species of spider. The number of issuing spiderlings

will always be much less than that of the eggs. The actual working

of natural selection and the forming of new species can of course

be seen only in results, and not in process. The great variety of

adaptation, the fitness of adaptive structures, can be readily

illustrated among the commonest animals. Animals showing certain

striking and unusual adaptations will perhaps make the matter more

obvious. To all teachers will occur numerous opportunities of

illustrating, by reference to actual processes or to obvious

results, the principles of this chapter.

=The multiplication and crowding of animals.=--In the reproduction or

multiplication of animals the production of young proceeds in

geometric ratio, that is, it is truly a multiplication. Any species of

animal, if its multiplication proceeded unchecked, would sooner or

later be sufficiently numerous to populate exclusively the whole

world. The elephant is reckoned the slowest breeder of all known

animals. It begins breeding when thirty years old and goes on breeding

until ninety years old, bringing forth six young in the interval, and

surviving until a hundred years old. Thus after about eight hundred

years there would be, if all the individuals lived to their normal age

limit, 19,000,000 elephants alive descended from the first pair. A few

years more of unchecked multiplication of the elephant and every foot

of land on the earth would be covered by them. But the rate of

multiplication of other animals varies from a little to very much

greater than that of the elephant. It has been shown that at the

normal rate in increase in English sparrows, if none were to die save

of old age, it would take but twenty years to give one sparrow to

every square inch in the State of Indiana. The rate of increase of an

animal, each pair producing ten pairs annually and each animal living

ten years, is shown in the following table:

Years. Pairs produced. Pairs alive at end of year.

1 10 11

2 110 121

3 1,210 1,331

4 13,310 14,641

5 146,410 161,051

10 ...... 25,937,424,600

20 ...... 700,000,000,000,000,000,000

Some animals produce vast numbers of eggs or young; for example, the

herring, 20,000; a certain eel, several millions; and the oyster from

500,000 to 16,000,000. Supposing we start with one oyster and let it

produce one million of eggs. Let each egg produce an oyster which in

turn produces[19] one million of eggs, and let these go on increasing

at the same rate. In the second generation there would be one million

million of oysters, and in the fourth, i.e. the great great

grandchildren of the first oyster, there would be one million million

million million of oysters. The shells of these oysters would just

about make a mass the size of the earth.

But it is obvious that all the new individuals of any animal produced do

not live their normal duration of life. All animals produce far more

young than can survive. As a matter of fact, which we may verify by

observation, the number of individuals of animals in a state of nature

is, in general, about stationary. There are about as many squirrels in

the forest one year as another, about as many butterflies in the field,

about as many frogs in the pond. Some species increase in numbers, as

for example, the rabbit in Australia, which was introduced there in 1860

and in fifteen years had become so abundant as to be a great pest. Other

species decrease, as the buffaloes, which once roamed our great plains

in enormous herds and are now represented by a total of a few hundred

individuals, and the passenger-pigeon, whose migrating flocks ten years

ago darkened the air for hours in parts of the Mississippi valley, where

now it is a rare bird. But the hand of man is the agent which has helped

to increase or to check the multiplication of these animals. In nature

such quick changes rarely occur.

=The struggle for existence.=--The numbers of animals are stationary

because of the tremendous mortality occasioned by the constant preying

on eggs and young and adults by other animals, because of strenuous and

destructive climatic and meteorological conditions, and because there is

not space and food for all born, not even, indeed, for all of a single

species, let alone all of the hundreds of thousands of species which now

inhabit the earth. There is thus constantly going on among animals a

fearful _struggle for existence_. In the case of any individual this

struggle is threefold: (1) with the other individuals of his own species

for food and space; (2) with the individuals of other species, which

prey on him, or serve as his prey, or for food and space; and (3)

finally with the conditions of life, as with the cold of winter, the

heat of summer, or drouth and flood. Sometimes one of these struggles is

the severer, sometimes another. With the communal animals the struggle

among individuals is lessened--they help each other; but when the

struggle with the conditions of life are easiest, as in the tropics or

in the ocean, the struggle among individuals becomes intensified. Each

strives to feed itself, to save its own life, to produce and safeguard

its young. But in spite of all their efforts only a few individuals out

of the hosts produced live to maturity. The great majority are destroyed

in the egg or in adolescence.

=Variation and natural selection.=--What individuals survive of the many

which are born? Those best fitted for life; those which are a little

stronger, a little swifter, a little hardier, a little less readily

perceived by their enemies, than the others. They are the winners in the

struggle for existence; they are the survivors. And this survival of the

fittest, as it is called, is practically a process of selection by

Nature. Nature selects the fittest to live and to perpetuate the

species. Their progeny again undergo the struggle and the selecting

process, and again the fittest live. And so on until adjustment or

harmonizing of animals' bodies and habits with the conditions of life,

with their environment, comes to be extremely fine and nearly perfect.

It is evident, of course, that such a natural selection or survival of

the fittest and consequent adaptation to environment presupposes

differences among the individuals of a species. And this is an

observed fact. No two individuals, although of the same brood, are

exactly alike at birth; there always exist slight variations in

structure and performance of functions. And these slight variations

are the differences which determine the fate of the individual. One

individual is a little larger or stronger or swifter or hardier than

its mates. The existence of this variation we know from our

observation of the young kittens or puppies of a brood. So it is with

all animals. Thus natural selection depends upon two factors, namely,

the excess in the production of new individuals and the consequent

struggle for existence among them, and the existence of variations

which give certain individuals slight advantages in this struggle.

=Adaptation and adjustment to surroundings.=--The action of natural

selection obviously must, and does, result in a fine adaptation and

adjustment of the structure and habits of animals to their

surroundings. If a certain species or group of individuals cannot

adapt itself to its environment, it will be crowded out by others that

can. A slight advantageous variation comes in time by the continuously

selective process to be a well-developed adaptation.

The diverse forms and habits possessed by animals are chiefly

adaptations to their special conditions of life. The talons and beak

of the eagle, the fishing-pouch of the pelican, the piercing

chisel-like bill of the woodpecker, and the sensitive probing-bill of

the snipe are adaptations connected with the special feeding habits of

these birds. The quills of the porcupine, the poison-fangs of the

rattlesnake, the sting of the yellow-jacket, and the antlers of the

deer are adaptations for self-defence. The fins and gills of fishes,

the shovel-like fore feet of the mole, the wings of birds and insects

and bats, the toe-pads of the tree-toad, the leaping-legs of the

grasshopper, all these are adaptations concerned with the special

life-surroundings of these animals.

Adaptations may relate to habits and behavior as well as to structure.

Plainly adaptive are such habits as the migration of birds and some

other animals, most of the habits connected with food-getting, and

especially striking and interesting those connected with the production

and care of the young, including nest-making and home-building.

=Species-forming.=--It is evident that through the cumulative action

of natural selection, animals of a structural type considerably (even

unlimitedly) different from any original type may in time be produced

by the gradual modification of the original type under new conditions.

If, for example, a few individuals of a mainland species should come

to be thrown as waifs of wave and storm upon an island, and if these

should be able to maintain themselves there and produce young,

increasing so as to occupy the new territory, there would be produced

in time a new type of individual conforming or adapted to the

conditions obtaining in the island, these conditions being, of course,

almost certainly different from those of the mainland. Thus as an

offshoot or derivation from the original type still existing on the

mainland we should have the new island-inhabiting type. Now when these

island individuals come to differ so much, structurally and

physiologically, from the mainland type that they cannot, even if

opportunity offers, successfully mate or interbreed with mainland

individuals the island type constitutes a new species. That is, our

distinction between species rests not only on structural differences,

but on the impossibility of interbreeding (at least for the production

of fertile young). Such a combination of the action of natural

selection and the condition of isolation (as illustrated by the case

of island animals), is probably the most potent factor in the

production of new species of animals (and plants).

For accounts of the struggle for existence, variations, adaptations,

natural selection and species-forming see Darwin's "Origin of Species,"

Wallace's "Island Life," and Romanes' "Darwin and After Darwin," I.

=Artificial selection.=--When a selection among the individuals of a

species, that is, the choosing and preserving of individuals which

show a certain trait or traits and the destroying of those individuals

not possessing this trait, is done by man, it is called artificial

selection. To artificial selection we chiefly owe all the many races

or varieties of our domesticated animals and plants. For example, from

the ancestral jungle fowl have been developed by artificial selection

(and by cross-breeding) all our kinds of domestic fowl, as Brahmas,

black Spanish, bantams, game-cocks, etc.; from the wild rock-dove have

been developed our various fancy pigeons, as carriers, pouters,

fantails, etc.

For an account of artificial selection see Darwin's "Plants and Animals

under Domestication," and Romanes' "Darwin and After Darwin," I.

FOOTNOTE:

[19] Oysters are hermaphroditic, each individual producing both sperm-

and egg-cells.

CHAPTER XXX

SOCIAL AND COMMUNAL LIFE, COMMENSALISM

AND PARASITISM

=Social life and gregariousness.=--TECHNICAL NOTE.--Students should

refer to examples of gregariousness from their own observations of

animals. The roosting together of crows and of blackbirds; the

gathering of swallows preparatory to migration; the flocking of

geese and ducks, with leaders, in their migratory flights, all can

be readily observed. From observation or general reading students

will be more or less familiar with prairie-dog villages, beaver-dams

and marshes, the one-time great herds of bison, etc.

The struggle for existence is always operative; but in some cases one

or more phases of it may be ameliorated. For example, the amelioration

of the struggle among individuals of one species obtains in a lesser

or greater degree in the case of those animals which exhibit a _social

life_, of which mutual aid and mutual dependence are the basis. The

honey-bee and the ants are familiar examples of animals which show a

high degree of social life. They live, indeed, a truly communal life,

where the fate of the individual is bound up in the fate of the

community. But there are many animals which show a much lower degree

of mutual aid and a far less coherent society. The simplest form of

social life exists among those animals in which many individuals of

one species keep together, forming a great band or herd. In this case

there is not nearly so much mutual aid or mutual dependence as in that

of the honey-bee, and the safety of the individual is not wholly bound

up in the fate of the herd. Such animals are said to be _gregarious_

in habit, and this gregariousness is undoubtedly advantageous to the

individuals of the band. The great herds of reindeer in the North, and

of the bison or buffalo which once ranged over the Western American

plains are examples of a gregariousness in which mutual protection

from enemies, like wolves, seems to be the principal advantage gained.

The bands of wolves which hunted the buffalo show the advantage of

mutual help in aggression as well as in protection. Prairie-dogs live

in great villages or communities which spread over many acres. By

shrill cries they tell each other of the approach of enemies, and they

seem to visit each other and to enjoy each other's society a great

deal, although that they are thus afforded much actual active help is

not apparent. The beavers furnish a well-known and very interesting

example of mutual help; they exhibit a communal life although a simple

one. They live in villages or communities, all helping to build the

dam across the stream which is necessary to form the marsh or pool in

which the nests or houses are built.

=Communal life.=--TECHNICAL NOTE.--See technical notes, pp. 212

_et seq_, for directions for work in connection with the study of

the communal life of ants, bees, and wasps.

When many individuals of a species live together in a community in which

the different kinds of work are divided more or less distinctly among

the different members and where each individual works primarily for the

whole and not for himself; where there is, in other words, a thorough

mutual help and mutual dependence among the members of the community

accompanied by a division of labor, the life of the species is truly

communal. Those animals which show the most elaborate and specialized

_communal life_ are the termites or white ants, the social bees and

wasps, and the true ants. Of these the ants and honey-bees stand first.

As already explained (see pp. 220 _et seq_), there are among these

communal insects several different kinds of individuals in each species.

With most animals there are two kinds only, males and females, which may

or may not show differences in color, form, etc., so that they are

readily distinguishable. Among all the communal insects, however, there

are always three kinds of individuals, males, females, and workers,

these last being infertile individuals. With the social wasps and social

bees the workers are all infertile females and are smaller than the

fertile forms; with the termites there are besides the fertile males and

females, which are winged, workers which are wingless, and also peculiar

wingless individuals called soldiers which have very large jaws and

whose business it is to fight off attacking enemies of the community.

Among the ants the workers are also wingless, while the males and

females are winged. The worker ants in many species are of two kinds,

so-called worker majors and worker minors, differing markedly in size.

All the ant workers are good soldiers, but with some the fighting is

done almost wholly by certain especially large-headed and large-jawed

ones which may be called soldier-workers.

Thus among all strictly communal animals there is a specialization or

differentiation of individuals accompanying the division of labor.

Special individuals have a certain part of the work of the community

to do, and they are specially modified in structure to do this work.

This structural modification may make them incapable of performing

certain other labor or work which is necessary for their living and

which must be done for them, therefore, by others. Thus the mutual

interdependence of the individuals composing a colony is very real.

The worker honey-bees cannot perpetuate the species; honey-bees would

die out were it not for the males and females. But the males and

females have given up the functions of food-getting and of caring for

their young; did not the workers do these things for them, the

community would die out quite as soon.

The advantages of communal or social life, of co-operation and mutual

aid are real. Those animals that have adopted such a life are among

the most successful of all in the struggle for existence. The termite

worker is one of the most defenseless and for those animals that prey

on insects one of the most toothsome insects, and yet the termite is

one of the most abundant and successfully living insect kinds in all

the tropics. Ants are everywhere and are everywhere successful. The

honey-bee is a popular type of successful life. The artificial

protection afforded it by man may aid it in its struggle for

existence, but it gains this protection because of certain features of

its communal life, and in nature the honey-bee takes care of itself

well. Co-operation and mutual aid are among the most important factors

which help in the struggle for existence.

=Commensalism.=--TECHNICAL NOTE.--Examine ants' nests to find

myrmecophilous insects. If on the seashore search for hermit-crabs

with sea-anemones on shell. If inland, try to have some preserved

specimens showing the crabs and sea-anemones.

The phases of living together and mutual help just discussed concerned

in each instance a single species of animal. All the members of a pack

of wolves or of a honey-bee community belong to a single species. But

there are numerous instances known of the mutually advantageous

association of individuals of two different species. Such an

association is called _commensalism_ or _symbiosis_.

The hermit-crabs live, as has been learned (p. 154), in the shells of

molluscs, most of the body of the crab being concealed within the

shell, only the head and the grasping and walking legs protruding. In

some species of hermit-crabs there is always to be found on the shell

near the opening a sea-anemone. "This sea-anemone is carried from

place to place by the crab, and in this way is much aided in obtaining

food. On the other hand, the crab is protected from its enemies by the

well-armed and dangerous tentacles of its companion. On the tentacles

there are many thousand long slender stinging threads, and the fish

that would eat the hermit-crab must first deal with the stinging

anemone." If the sea-anemone be torn away from the shell the crab will

wander about seeking another anemone. When he finds one, he struggles

to loosen it from the rock to which it is attached, and does not rest

until he has torn it loose and placed it on his shell.

In the case of the hermit-crab and the sea-anemone there is no doubt

of the mutual advantage derived from their communal life. But this

mutual advantage is not so obvious in some cases of commensalism,

where indeed most or all of the advantage often seems to lie with one

of the animals, while the other derives little or none, but on the

other hand suffers no injury. For example, "small fish of the genus

_Nomeus_ may often be found accompanying the beautiful Portuguese

man-of-war (_Physalia_) as it sails slowly about on the ocean's

surface. These little fish lurk underneath the float among the various

hanging thread-like parts of the man-of-war which are provided with

stinging cells. They are protected from their enemies by their

proximity to these stinging threads, but of what advantage to the

man-of-war their presence is is not understood." Similarly in the

nests of the various species of ants and termites many different kinds

of other insects have been found. "Some of these are harmful to their

hosts, in that they feed on the food-stores gathered by the

industrious and provident ant, but others appear to feed only on

refuse or useless substances in the nest. Some may be of help to their

hosts by acting as scavengers. Over one thousand species of these

myrmecophilous (ant-loving) and termitophilous (termite-loving)

insects have been recorded by collectors as living habitually in the

nests of ants and termites."

=Parasitism.=--TECHNICAL NOTE.--As examples of temporary external

parasites find and examine fleas and ticks on dogs and cats, red

mites on house-flies and grasshoppers (at the bases of the wings),

etc. As examples of permanent external parasites find bird-lice on

pigeons or domestic fowls or on other birds. Note the absence of

wings and the peculiarly modified body shape of these parasites.

Examine a bird-louse under the microscope; note the absence of

compound eyes (it has simple eyes) and absence of wings; note bits

of feathers, its food, in stomach, showing through the body. Find,

as examples of internal parasites, intestinal worms or flukes.

Examine trichinized pork to see _Trichinæ_ in muscles. Examine

preserved specimens of tapeworms. Collect pupæ of some common

butterfly or moth and keep them in the schoolroom until either the

butterflies or ichneumon flies issue. Some will surely be

parasitized, and yield ichneumon flies (parasites) instead of a

butterfly. As examples of degeneration by quiescence examine

barnacles (found on outer rocks of seashore at low tide; easily

obtained as preserved specimens by inland schools) and the females

of scale-insects. These insects may be found on oleanders (the

black scale, _Lecanium oleæ_) or fruit-trees (the San Jose scale,

_Aspidiotus perniciosus_). Note the great degeneration of the

adult female of the San Jose scale; it has no eyes, antennæ,

wings, or legs. The young may be found crawling about at certain

times of the year; they have eyes, antennæ and legs.

In addition to the various ways of living together among animals,

already described, namely, the social and communal life of individuals

of a single species and the commensal and symbiotic life of

individuals of different species, there is another and very common

kind of association among animals. This is the association of parasite

and host; the association between two sorts of animals whereby one,

the parasite, lives on or in the other, the host, and at the expense

of the host. In this association the parasite gains advantages great

or small, sometimes even obtaining all the necessities of life, while

the host gains nothing, but suffers corresponding disadvantage, often

even the loss of life itself. _Parasitism_ is a phenomenon common in

all the large groups of animals, though the parasites themselves are

mostly invertebrates. There are parasitic Protozoa, worms,

crustaceans, insects, and molluscs, and a few vertebrates.

Some parasites, like the fleas and lice, live on the surface of the body

of the host. These are called _external parasites_. Others, as the

tapeworms, live exclusively inside the body; such are called _internal

parasites_. Again, some, as the bird-lice, which are external parasites

feeding on the feathers of birds, spend their whole lifetime on the

host; they are called _permanent parasites_. Others, as a flea, which

leaps on or off its host as caprice directs, or like certain parasites

which as young live free and active lives, finally attaching themselves

to some host and remaining fixed there for the rest of their lives, are

called _temporary parasites_. Such a grouping is purely arbitrary and

exists simply for the sake of convenience. It is not rigid, nor does it

class parasites in their proper natural groups.

When various parasites are examined it will be noted that practically in

all cases the body of a parasite is simpler in structure than the body

of other animals closely related to it; that is, species which live

parasitically, obtaining their food from and being carried about by a

host, have simpler bodies than related forms that live free active

lives, competing for food with other animals about them. This simplicity

is not primitive, but results from the loss or atrophy of the structures

which the special mode of life of the parasite renders useless. Many

parasites are attached firmly by hooks or suckers to their host, and do

not move about independently of it. They have no need of the power of

locomotion, and accordingly are usually without wings, legs, or other

locomotory organs. Because they have no need of locomotion they have no

need of organs of orientation, those special sense organs like the eyes,

ears, and feelers which serve to guide and direct the moving animal; and

most fixed parasites will be found to have no eyes, or any of those

organs accessory to locomotion, and which serve for the detection of

food or of enemies. Because these important organs, which depend for

their successful activity on a well-organized nervous system, are

lacking, the nervous system of parasites is usually very simple. Again,

because the parasite usually feeds on the already digested food or the

blood of its host, most parasites have a very simple alimentary canal,

or even none at all. Finally, as the fixed parasite leads a wholly

sedentary and inactive life, the breaking down and rebuilding of tissue

in its body goes on very slowly and in minimum degree, so that there is

little need of highly developed respiratory and circulatory systems; and

most fixed and internal parasites have these systems of organs decidedly

simplified. Altogether the body of a fixed permanent parasite is so

simplified and so wanting in all those special structures which

characterize the active, complex animals that it often presents a very

different appearance from those forms with which we know it to be nearly

related. This simplicity due to loss or reduction of parts is called

_degeneration_. Such simplicity of body-structure due to degeneration

is, however, essentially different in its origin from the simplicity of

the lower simpler animals. In them the simplicity of body is primitive;

they are generalized animals; the simplicity of degeneration is

acquired; it is really an adaptation, or specialization.

An excellent example of body degeneration due to the adoption of a

parasitic habit is that of _Sacculina_ (fig. 159), a crustacean

parasitic on other crustaceans, namely, crabs. The young _Sacculina_

is an active, free-swimming larva essentially like a young prawn or

crab. After a short period of independent existence it attaches itself

to the abdomen of a crab, and lives as a parasite. It completes its

development under the influence of this parasitic life, and when adult

bears absolutely no resemblance to such a typical crustacean as a crab

or crayfish. Its body external to the host crab is simply a pulsating

tumor-like sac, with no mouth-parts, no legs, and internally hardly

any well-developed organs except those of reproduction. Degeneration

here is carried very far.

[Illustration: FIG. 159.--_Sacculina_, a parasitic crustacean; _A_,

attached to a crab, the root-like processes of the parasite

penetrating the body of the host; _B_, the active larval condition;

_C_, the adult removed from its host. (After Haeckel.)]

Various parasites have been referred to in Part II under their proper

branch and class. The worms include an unusually large number of them,

such as the tapeworms, trichinæ and other intestinal forms, all of

which live as internal parasites in the alimentary canal or in other

organs of higher animals, especially the vertebrates. Many crustaceans

are parasitic, usually living, like the fish-lice, as fixed external

parasites on fishes, other crustaceans, etc., but with a free and

active larval stage. Among the insects, on the contrary, many of the

parasitic forms (as the ichneumon flies) are free and active in the

adult stage, but live as internal grubs or maggots in the larval

stage. The ichneumon flies (of the order Hymenoptera) are four-winged,

slender-bodied insects which lay their eggs either on or in (by means

of a sharp piercing ovipositor) some caterpillar or beetle grub, into

the body of which the young grub-like ichneumon larvæ burrow on

hatching. The parasites feed on the body-tissues of the host, not

attacking, however, such organs as the heart or nervous system, which

would produce the immediate death of the host. The caterpillar lives

with the ichneumon grubs within it usually until nearly time for its

pupation. Often, indeed, it pupates with the parasite still in its

body. But it never comes to maturity. The larval ichneumons pupate

either within the body of its host, or in a tiny silken cocoons

outside of its body (fig. 160). From the cocoons the winged adult

ichneumons issue; and after mating the females find another

caterpillar on whose body to lay their eggs.

[Illustration: FIG. 160.--Larva of a sphinx-moth, with cocoons of a

parasitic ichneumon fly. (From specimen.)]

Degeneration can be produced by other causes than parasitism. It is

evident that if for any other reason an animal should adopt an

inactive fixed life it would degenerate. The barnacles (see fig. 37)

are excellent examples of degeneration through quiescence. They are

crustaceans related most nearly to the crabs and shrimps. The young

barnacle just from the egg is a six-legged, free-swimming larva

(nauplius) with a single eye, greatly like a young prawn or crab. It

develops during its independent life two compound eyes and two large

antennæ. But soon it attaches itself to some stone or shell, or pile

or ship's bottom, giving up its power of locomotion, and its further

development is a degeneration. It loses its compound eyes and antennæ,

and acquires a protecting shell. Its swimming feet become modified

into grasping organs, and it loses most of its outward resemblance to

the typical members of its class. The Tunicata or ascidians compose a

whole group of animals which are fixed in their adult condition and

have thus become degenerate. They have been likened to a "mere rooted

bag with a double neck." In their young stage they are free-swimming,

active, tadpole-like or fish-like larvæ, possessing organs much like

those of the adult simplest fish or fish-like animals. Their larval

structure reveals, however, the relationships of the ascidians to the

vertebrates, a relationship which is not at all apparent in the

degenerate adults. Certain insects live sedentary or fixed lives. All

the members of one large family, the Coccidæ, or scale-insects (figs.

62 and 63), have females which as adults are wingless and in some

cases have no legs, eyes, or antennæ, while the males are all winged

and have legs and the special sense organs. The males lead a free

active life, but the females have nearly or quite given up the power

of locomotion, attaching themselves by means of their sucking beak to

some plant, where they obtain a sufficient food-supply (plant-sap) and

lay their eggs. In both males and females the larvæ are little active

crawling six-legged creatures with legs, eyes, and antennæ.

We are accustomed perhaps to think of degeneration as necessarily

implying a disadvantage in life. It is true that a blind, footless,

degenerate animal could not cope with the active, keen-sighted, highly

organized non-degenerate in free competition. But free competition is

exactly what the degenerate animal has nothing to do with. Certainly the

_Sacculina_ and the scale-insects live well; they are admirably adapted

to the kind of life they lead. A parasite enjoys certain obvious

advantages in life, and even extreme degeneration is no drawback (except

as we shall see later), but gives it a body which demands less food and

care. As long as the host is successful in eluding its enemies and

avoiding accident and injury the parasite is safe. Its life is easy as

long as the host lives. But the disadvantages of parasitism and

degeneration are nevertheless obvious. The fate of the parasite is bound

up with the fate of the host. "When the enemy of the host crab prevails,

the _Sacculina_ goes down without a chance to struggle in its own

defence. But far more important than the disadvantage in such particular

or individual cases is the fact that the parasite cannot adapt itself in

any considerable degree to new conditions. It has become so modified, so

specialized to adapt itself to the very special conditions under which

it now lives, it has gone so far in giving up organs and functions, that

if present conditions change and new ones come to exist the parasite

cannot adapt itself to them. The independent free-living animal holds

itself, one may say, able and ready to adapt itself to any new

conditions of life. The parasite has risked everything for the sake of a

sure and easy life under the present existing conditions. Change of

conditions means its extinction."

[Illustration: FIG. 161.--Young fur seals, _Callorhinus ursinus_, of

the Tolstoi rookery, St. Paul Island, Bering Sea, killed by a

parasitic intestinal worm, _Uncinaria_ sp. (Photograph by the Fur Seal

Commission.)]

For an elementary account of commensalism and parasitism see Jordan

and Kellogg's "Animal Life," pp. 172-200. The account here given is

based on the author's previously written account in "Animal Life." See

also Van Beneden's "Animal Parasites and Messmates."

CHAPTER XXXI

COLOR AND PROTECTIVE RESEMBLANCES

TECHNICAL NOTE.--For an appreciation of the reality of protective

resemblances observations must be made in the field. Examples are

easily found. Locusts, katydids, green caterpillars, lizards,

crouching rabbits, and brooding birds are readily observed instances

of general protective resemblance. For examples of variable

resemblance examine specimens of a single locust species taken from

different localities; the individuals of the various species of the

genus _Trimerotropis_ show much variation to harmonize with their

surroundings. Collect a number of larvæ (caterpillars) of one of the

swallow-tail butterflies (_Papilio_), and when ready to pupate put

them separately into pasteboard boxes lined inside with differently

colored paper. The chrysalids will show in their coloration the

influence of the different colors of the lining paper, their

immediate environment. As examples of special protective resemblance

observe inch- or span-worms (larvæ of Geometrid moths). The

walking-stick is not uncommon; many spiders that inhabit flower-cups

show striking protective color patterns; and the Graptas or

comma-butterflies which resemble dead leaves may be examined.

To illustrate warning colors, find, if possible, the larvæ

(caterpillars) of the common milkweed or monarch butterfly (_Anosia

plexippus_), and offer them to birds, at the same time offering

other caterpillars, and note the results. For terrifying or

threatening appearance find specimens of the large green tobacco-

or tomato-worm (larva of the five-spotted sphinx-moth,

_Phlegethontius carolina_), or other sphingid larvæ.

The butterflies illustrating the striking example of mimicry,

described on p. 432, can be found in most parts of the country.

Syrphid and other flies which mimic bees and wasps can readily be

found on flowers.

Each student should search for himself for examples of protective

resemblance.

=Use of color.=--The prevalence of color and the oftentimes striking

and intricate coloration patterns of animals demand some explanation.

As naturalists are accustomed to find the frequently bizarre and

seemingly inexplicable shapes and general structure of animals readily

explained by the principle of adaptation, that is, special

modification of body-structure to fit special conditions of life, so

they look to use as the chief explanation of color and markings. Some

uses are obvious; bright colors and striking patterns may serve to

attract mates or to avail as recognition marks by which individuals of

a kind may readily recognize each other. The white color of arctic

animals probably serves to help keep them warm by preventing radiation

of heat from the body; on the other hand dark color may also help to

keep animals warm by absorbing heat. "But by far the most widespread

use of color is for another purpose, that of assisting the animal in

escaping from its enemies or in capturing its prey."

It is common knowledge that the young and old, too, of many kinds of

ground-inhabiting animals, when startled by an enemy will not run, but

crouching close to the ground remain immovable, trusting to remain

unperceived. But a blue or crimson rabbit, however still it might

keep, would be easily seen by its enemy and killed. Rabbits, however,

which are good examples of animals having this habit of lying close,

are neither blue nor green nor red, but are colored very much like the

ground on which they crouch. This harmonious coloration is as

necessary to the success of this habit as is the keeping still. A

grasshopper flying or leaping in the air is conspicuous; when it

alights how inconspicuous it is! Unless one has followed it closely in

its flight and has kept the eye fixed on it after alighting it is

usually impossible to distinguish it from its surroundings. And this

is greatly to the advantage of the grasshopper in its efforts to

escape its enemies, that is, in its struggle for existence. On the

other hand a green katydid would be very conspicuous in a dusty road.

But dusty roads are precisely where katydids do not rest. They alight

among the green leaves of a tree or shrub. The animals that live in

deserts are almost all obscurely mottled with gray and brownish and

sand-color so as to harmonize in color with their habitual

environment. The arctic hares and foxes and grouse which live in

regions of perpetual snow are pure white instead of red or brown or

gray like their cousins of temperate and warm regions.

These cases of an animal's color and markings harmonizing with the

usual environment are called instances of _protective resemblance_;

that is, they are resemblances for a purpose, that purpose being to

render the animal indistinguishable from its surroundings and thus to

aid it in escaping its enemies. Such protective resemblances are

obviously of great value to animals, and, like other advantageous

modifications, have been produced by the action of natural selection.

Those individuals of a species most conspicuous and hence most readily

perceived by enemies are the first (under ordinary circumstances) to

be captured and eaten. The less conspicuous live and produce young

like themselves. Of these young the least conspicuous are again saved

and so over and over again through thousands of generations until this

natural selecting of the protectively colored results in the

production of the wonderfully specialized examples of resemblance to

which attention is called in the following paragraphs.

=General, variable, and special protective resemblance.=--In the

brooks most fishes are dark olive or greenish above and white below.

To the birds and other enemies which look down on them they are

colored like the bottom. To their fish-enemies which look up from

below they are like the white light above them in color and their

forms are not clearly seen. The green tree-frogs and tree-snakes which

live habitually among green foliage; the mottled gray and tawny

lizards and birds and small mammals of the plains and deserts, and the

white hares and foxes and owls and ptarmigan of the snowy arctic

regions--all show a general protective resemblance.

[Illustration: FIG. 162.--The twig or walking-stick insect,

_Diapheromera femorata_. (From specimen.)]

Sometimes an animal changes color when its surroundings change.

Certain hares and grouse of northern latitudes are white in winter

when the snow covers all the ground, but in summer when much of the

snow melts, revealing the brown and gray rocks and withered leaves,

they put on a grayish and brownish coat of hair or feathers. A small

insect called the toad-bug (_Galgulus_) lives abundantly on the banks

of a pond on the campus of Stanford University. The shores of this

pond are covered in some places with bits of bluish rock, in others

with bits of reddish rock, and in still others with sand. Specimens of

the toad-bug collected from the blue rocks are bluish or leaden in

color, those from the red rocks are reddish, and those from the sand

are sand-colored. Changes of color to suit the surroundings can be

quickly made by some animals. The chameleons of the tropics change

momentarily from green to brown, blackish, or golden. There is a

little fish (_Oligocottus snyderi_) common in the tide-pools of the

Bay of Monterey in California whose color changes quickly to harmonize

with the rocks it happens to rest above. Such changing coloration to

suit the surroundings may be called _variable protective resemblance_.

Very striking are those cases of protective resemblance in which the

animal resembles in color and shape, sometimes in extraordinary

detail, some particular object or part of its usual environment. This

may be called _special protective resemblance_. The larvæ of the

Geometrid moths called inch-worms or span-worms are twig-like in

appearance, and have the habit, when disturbed, of standing out

stiffly from the twig or branch on which they rest, so as to resemble

in attitude as well as color and markings a short or broken twig. To

increase this simulation the body of the larva often has a few

irregular spots or humps resembling the scars left by fallen leaves,

and it also lacks the middle prop-legs of the body common to other

lepidopterous larvæ, which would tend to destroy the illusion so

successfully carried out by it. The common twig-insect or

walking-stick (fig. 162) with its wingless, greatly elongate, brown or

greenish body and legs is when at rest quite indistinguishable from

the twigs on which it lies. Another excellent example of special

protective resemblance is furnished by the famous green-leaf insect

(_Phyllium_) of the tropics, which has broad leaf-like wings and body

of a bright green color with markings which imitate the leaf-veins,

and small irregular yellowish spots which simulate decaying or stained

or fungus-covered spots in the leaf. Most striking of all, however, is

the large dead-leaf butterfly _Kallima_ (fig. 163) of the East Indian

region. The upper sides of the wing are dark with purplish and

orange markings not at all resembling a dead leaf. But the butterflies

when at rest hold their wings together over the back, so that only the

under sides of them are exposed. These are exactly the color of a dry

dead leaf with markings mimicking midrib and oblique veins, and, most

remarkable of all, what are apparently two holes like those made in

leaves by insects, but in the butterfly imitated by two small circular

spots free from scales and hence clear and transparent. When _Kallima_

alights it holds the wings in such position that the combination of

all four produces with remarkable fidelity the simulation of a dead

leaf still attached to the twig by a short pedicel or leaf-stalk

(imitated by a short "tail" on the hind wings). The head and legs of

the butterfly are concealed beneath the wings.

[Illustration: FIG. 163.--The dead-leaf butterfly, _Kallima_ sp., a

remarkable case of special protective resemblance. (From specimen.)]

=Warning colors, terrifying appearances, and mimicry.=--While many

animals are so colored as to harmonize with their habitual or usual

environment, others on the contrary are very brightly colored and marked

in such bizarre and striking pattern as to be conspicuous. There is no

attempt at concealment; it is obvious that conspicuousness is the object

sought or at least produced by the coloration. Animals like these, we

shall find, are in almost all cases specially protected by special

weapons of defence such as stings or poison-fangs, or by the secretion

of an acrid, ill-tasting fluid in the body. Many caterpillars have been

found, by observation in nature and by experiment, to be distasteful to

insectivorous birds. Now it is obvious that it would be advantageous to

these caterpillars to be readily recognized by birds. After a few trials

the bird learns by experience to let these distasteful larvæ alone;

their conspicuous markings serve as _warning colors_. The

black-and-yellow-banded caterpillar of the common milkweed or monarch

butterfly (_Anosia plexippus_) is a good example of such protection by a

combination of distastefulness and warning coloration. The little

lady-bird beetles are mostly distasteful to birds; they are brightly and

conspicuously marked. Certain little Nicaraguan frogs have a bright

livery of red and blue, in strong contrast to the dull concealing colors

of other frogs in their region. By offering these little blue and red

frogs to hens and ducks the naturalist Belt found that they are

distasteful to the birds.

[Illustration: FIG. 164.--The larva of the pen-marked sphinx-moth,

_Sphinx chersis_, showing terrifying attitude. (After Comstock.)]

Certain animals which are without special means of defence and are not

distasteful are yet so marked or shaped, and so behave as to present a

threatening or _terrifying appearance_. The large green caterpillars

of the sphinx-moths, the tomato- and tobacco-worms, are familiar

examples, each larva having a sharp horn on the back of the next to

last body-segment (fig. 164). When disturbed the caterpillar assumes a

threatening attitude, and the horn seems to be an effective weapon of

defence. As a matter of fact it is not at all a weapon of defence,

being weak, not provided with poison, and altogether harmless.

But it would plainly be to the advantage of a defenceless animal, one

without poison-fangs or sting and without an ill-tasting substance in

its body, to be so marked and shaped as to mimic some other specially

defended or inedible animal sufficiently to be mistaken for it and

thus to escape attack. Such cases have been noted, especially among

insects. This kind of protective resemblance may be called _mimicry_.

A most striking case is that presented by the familiar monarch and

viceroy butterflies (fig. 165). The monarch (_Anosia plexippus_) is

perhaps the most abundant and widespread butterfly of our country. It

is a fact well known to entomologists that it is distasteful to birds

and is let alone by them. It is conspicuous, being large and chiefly

red-brown in color. The viceroy (_Basilarchia archippus_), also

red-brown and patterned almost exactly like the monarch, is not, as

its appearance would seem to indicate, a very near relation of the

latter, but on the contrary it belongs to a genus of butterflies all

of which, except the viceroy and one other, are black and white in

color and of different pattern from the monarch. The viceroy is not

distasteful to birds, but by its extraordinary simulation or mimicking

of the monarch it is not distinguished from it and so is not molested.

In the tropics there have been discovered numerous examples of mimicry

among insects. The members of two large families of butterflies

(Danaidæ and Heliconidæ) are distasteful to birds and are mimicked by

members of other butterfly families (especially the Pieridæ).

[Illustration: FIG. 165.--The monarch butterfly, _Anosia plexippus_

(above), distasteful to birds, and the viceroy, _Basilarchia

archippus_ (below), which mimics it. (From specimens.)]

=Alluring coloration.=--A few animals show what is called alluring

coloration; that is, they display a color pattern so arranged as to

resemble or mimic a flower or other lure, and thus entice to them other

animals, their natural prey. Certain Brazilian fly-catching birds have a

brilliantly colored crest which can be displayed in the shape of a

flower-cup. The insects attracted by the false flower furnish the bird

with food. In the tribe of fishes called the "anglers" or "fishing

frogs," the front rays of the dorsal fin are prolonged in the shape of

long slender filaments, the foremost and longest of which has a

flattened and divided extremity. The angler conceals itself in the mud

or in the cavities of a coral reef, and waves the filament back and

forth. Small fish are attracted by the lure, mistaking it for worms

writhing about. When they approach they are engulfed in the mouth of the

angler, which in some species is of enormous size. One of these angler

species is known to fishermen as the "all-mouth."

For a fuller account of protective resemblances and mimicry see Jordan

and Kellogg's "Animal Life," pp. 201-223. For still more extended

accounts see Poulton's "Colours of Animals," and Beddard's "Animal

Coloration."

CHAPTER XXXII

THE DISTRIBUTION OF ANIMALS

TECHNICAL NOTE.--The larger aspects or phenomena of the distribution

of animals over the earth on land and in sea cannot be studied

personally in the field by the student, but many local features of

distribution can be so observed and studied. The restriction of

certain kinds of animals to certain kinds of habitat, the presence

and character and effectiveness of barriers, some of the modes of

distribution, the presence and successful life of introduced foreign

species such as the black and brown rats, the English sparrow, the

German and Asiatic cockroaches, the gradual change of range or

distribution of certain kinds of animals through the influence of a

change in environment (caused by man in cutting off forests,

cultivating heretofore wild pastures, etc.) all offer favorable and

profitable opportunities for personal observation.

An excellent and feasible piece of field-work in distribution is

the making of a zoological survey of the locality in which the

school is situated. A map of the locality should be made on a

generous scale, which should include all prominent physical

features of the region, such as streams, ponds, hills, woodlands,

marshes, etc., and on this map should be indicated the places where

the various animals of the local fauna occur. Some of the animal

species will have a limited range, and the limits of this range

should be shown. This map and faunal list can be added to and

perfected by successive classes. For fuller discussions of the

geographical distribution of animals see Jordan and Kellogg's

"Animal Life," Beddard's "Zoogeography," Heilprin's "The

Distribution of Animals," and Wallace's "Geographical

Distribution."

=Geographical distribution.=--It is a matter of common knowledge with

all of us that there are no wild lions or camels or kangaroos or monkeys

or ostriches or nightingales in North America. Ostriches are found only

in Africa and South America, kangaroos only in Australia, lions only in

Asia and Africa. On the other hand there are no opossums in Europe or

grizzly bears or rattlesnakes anywhere else in the world than in this

country. That is, certain kinds of animals have a certain limited range

of occurrence or distribution. It is obvious, too, that certain animals

live only on land, while others live only in water, and of these latter

some are restricted to the ocean, while others live only in fresh water.

All of the facts regarding the dispersion or diffusion of animals on

land and in water make up the science of the _geographical distribution

of animals_, or, as it is sometimes called, _zoogeography_. Under this

subject are included not only the facts of the present actual

distribution or occurrence of animals over the world, but the facts

concerning the reasons for this distribution, the modes of travel and

dispersion, the character and influence of barriers to the spread, and

the results, in the adaptation of old forms and the production of new

forms, of the phenomena of distribution.

Just as maps are made to show graphically the facts of political

geography, which concerns the position and extent of the various

powers and States which claim the allegiance of the people, and the

facts of physical geography, which concerns the physical character of

the earth's surface, so maps are made to show the geographical

distribution of animals. Because of the great numbers of animal

species no one map can show the distribution of all species, but a

series of maps of the world or of a continent or of a State or county

or more limited region could be made (and many such have been made)

showing the distribution of selected species. In a map of a limited

locality, say of a few square miles, the occurrence and distribution

of most of the commoner and more familiar animals can be shown, and

each high school should possess such a map (see technical note at

beginning of this chapter).

=Laws of distribution.=--The laws governing the distribution of animals

over the earth's surface have been recently[20] expressed in a simple

statement as follows: Every species of animal is found in every part of

the earth unless (_a_) its individuals have been unable to reach this

region on account of barriers of some sort; or (_b_) having reached it,

the species is unable to maintain itself, through lack of capacity for

adaptation, through severity of competition with other forms, or through

destructive conditions of environment; or (_c_) having entered and

maintained itself it has become so altered in the process of adaptation

as to become a species distinct from the original type.

=Modes of migration and distribution.=--That animals should be

continually trying to extend their range is obvious from what we know

of their rapid increase by multiplication. In a region which can

provide food for but one thousand wolves, there is a production each

year of several times one thousand. These new wolves must struggle

among themselves for food, or migrate, if possible, to new regions as

yet not inhabited by wolves. The wolf's mode of migration or

distribution is walking or running, and so with other mammals except

the bats and aquatic forms. Birds and bats can fly, and can thus

migrate more swiftly, farther, and over barriers which would stop

mammals. Most insects can fly. Worms can only crawl and very slowly at

that. Fishes can swim, but if they are in a landlocked sheet of water,

they cannot go beyond its confines. Marine animals can migrate from

ocean to ocean, and land animals from continent to continent unless

checked by barriers (see next paragraph).

But besides such voluntary and independent modes of distribution long

journeyings may be made involuntarily, or by a passive migration as it

may be called. Parasites, for example, are carried by their hosts in

all their travels; the tiny Tardigrada and Rotifera, which can be

desiccated and yet restored to active life by coming again into water,

are carried in the dried mud on the feet of birds or other animals. On

floating objects in rivers or in ocean currents land-animals may be

carried long distances. Man, the greatest traveller of all, is

responsible for the widened distribution of many animals. Thus have

come to us in ships from Europe the black and brown rats, the English

sparrow, the Hessian fly, the commonest cockroaches of our houses and

many other forms. And these animals have been carried involuntarily

all over the United States in railway-cars and wagons.

=Barriers to distribution.=--As is indicated in the paragraph on the

modes of migration, a considerable sheet of water is obviously a

barrier to the further travelling of a walking or crawling

land-animal, although no barrier to a winged form. Similarly a strip

of land is a barrier to a strictly aquatic animal as a fish. Or a high

fall in the stream may serve as an insuperable barrier, making it

impossible for any fish below the fall to reach the upper part of the

stream. Numerous cases of this kind are known in the Rocky Mountains

and Sierra Nevada, where a stream may be well supplied with trout

below a fall, and quite bare of these fish above the fall. In the

Yosemite Valley in California trout live in the Merced River below the

great Vernal and Nevada falls, but above these falls the Merced

contains no trout. To fresh-water swimming animals salt water may be a

barrier; thus some kinds of fresh-water fishes are limited to one of

two near-by streams although the mouths of these streams empty near

each other into the ocean. The amphibious batrachians, at home in

fresh water and on land, are killed by contact with sea-water.

Earthworms also are killed by salt water. Thus the narrowest ocean

strait is as effective a barrier to these animals as a whole sea.

High mountain ranges and broad deserts are barriers to many

land-animals, partly because of the physical obstacles, partly because

of the differences in temperature and in food-supply.

Temperature and climate (as distinct from temperature) and the ocean are

the three great barriers when we consider the animal kingdom as a whole,

and look for the causes which determine the chief zoogeographical

divisions of the earth's surface. Most of the tropical animals cannot

endure frost, hence the isothermal line of frost is a line across which

few tropical animals venture. Most arctic animals are enfeebled by heat,

and the isothermal line which marks off the region in which frost occurs

the year round is another great zoogeographical boundary. But while

these lines are limits for localized species, some animals, as birds,

especially, keep within a relatively uniform temperature by migrations

across these lines. It should be borne in mind that the gradual decrease

in temperature met with in going north or south from the tropics is also

met in the ascent of high mountains. The summits of lofty peaks, even in

the tropics, are truly arctic in character; they are snow-covered, and

the animals and plants on them are truly arctic. Thus in the ascent of a

single mountain a whole series of life-zones from tropical to arctic can

be traversed.

Climate, as distinct from temperature, establishes limits of

distribution. The animals of Eastern North America accustomed to a humid

atmosphere cannot live in the dry plains and deserts of the West.

Closely associated with climate is the nature of the plant-growth

covering the land; here are forests and luxuriant meadows, there are

sparse tough grasses of the dry plateau. The limits of a special kind of

plant-growth often are the limits of distribution of certain animals.

The third great barrier, the ocean, is perhaps the most obvious of all

in its influence. It is only in rare cases that any land-animal can

independently cross a great ocean. Thus the land-animals of Australia

differ from those of all other countries, and those of Africa and

South America have developed almost independently of one another. The

ocean is, as already mentioned, also a barrier for fresh-water aquatic

animals, and even marine fishes which live normally in shallow waters

along the shore rarely venture across the great depths of mid-ocean.

The obstacles or barriers met with determine the limits of a species.

Each species broadens its range as far as it can. It attempts

unwittingly, through natural processes of increase, to overcome the

obstacles of ocean or river, of mountain or plain, of woodland or

prairie or desert, of cold or heat, of lack of food or abundance of

enemies--whatever the barriers may be. The degree of hindrance offered

by any barrier differs with the nature of the animal trying to pass

it. That which forms an impassable obstacle to one species may be a

great aid to the spread of another. "The river which blocks the monkey

or the cat is the highway of the fish and turtle. The waterfall which

limits the ascent of the trout is the chosen home of the ouzel."

=Faunæ and zoogeographic areas.=--The term _fauna_ is applied to the

animals of any region considered collectively. Thus the fauna of

Illinois includes the entire list of animals found naturally in that

State. The fauna of a schoolyard comprises all the animals found

living naturally in the yard. The fauna of a pond includes all the

animal inhabitants of the pond. (_Flora_ is used similarly of all the

plants in a given region.) The relation of one fauna to another

depends on the character and effectiveness of the barriers between,

and the physical character of the two regions. Thus the fauna of

Illinois differs but little from that of Indiana or Iowa, because

there are no barriers between the States, and they are alike

physically. On the other hand the fauna of California differs much

from that of the Eastern States because of the great barriers (the

desert and the Sierra Nevada Mountains) which lie between it and these

States, and because of the great differences in the physical and

climatic conditions of the two regions.

The land-surface of the earth has been divided by zoogeographers into

seven great realms of animal life, based on the distributional

characters shown by these various regions. These realms are separated

by barriers of which the chief are the presence of the sea and the

occurrence of frost. These realms are named, from their geographical

region, the Arctic, the North Temperate, the South American, the

Indo-African, the Madagascar, the Patagonian, and the Australian. Of

these the Australian alone is sharply defined. Most of the others are

surrounded by a broad fringe of debatable ground that forms a

transition to some other zone.

=Habitat and species.=--The habitat of a species of animal is the

region in which it is found in a state of nature. It is currently

believed that the habitat of any animal is the whole of that region

for which it is best adapted. But this is not necessarily true. In

fact in most cases it is not true. The trout naturally debarred from

the rivers in Yellowstone Park by the waterfalls could live there well

if the barrier could be passed. In the case of one stream it has been

passed and the trout flourish above the fall. The success of the black

and brown rats and the English sparrow in America, of the rabbit in

Australia, of bumblebees and house-flies in New Zealand, all of which

animals had a natural habitat not including these regions, but by

artificial means have been carried over the barriers and into the new

territory, prove that "habitat" is not necessarily coincident with

"only fit region." Shad, striped bass, and catfish from the Potomac

River have been introduced into and now thrive in the Sacramento River

in California. In fact the whole work of the introduction and

diffusion of valuable food-animals in territory not naturally included

in the habitat of the species is based on our knowledge that the

habitat of a species is often determined by physical barriers rather

than by exclusive fitness of environment. Within the natural habitat

the environment _is_ fit for the species' existence, outside of it the

environment _may_ be fit.

But there occur numerous instances where a species successful in leaving

its original habitat is unsuccessful in attempting to maintain itself on

new ground. Man has introduced various animals from one country to

another. The English sparrow (naturally debarred from this country by

the ocean barrier), brought to America from Europe, has covered its new

territory rapidly and maintains itself with brilliant success. But the

nightingale, the starling and skylark which have been repeatedly

introduced and set free are unable to maintain themselves here.

=Species-extinguishing and species-forming.=--Accompanying the

constant slow migrating of species into new habitats and the constant

slow changing of environment and conditions everywhere is to be seen a

constant modification of the fauna of any region due to the inability

of some species to maintain their ground, the predominating increase

of others, and the modifying or adaptive changing of others into new

forms. In 1544 the black rat of Europe was introduced into America and

it soon crowded out the native rats, being in its turn crowded out by

the European brown rat (the present common rat in buildings),

introduced about 1775. Here we have the original native species unable

to maintain itself in competition with introduced forms.

With a change of environing conditions, certain species are unable to

maintain themselves. With the destruction of the forests going on in

parts of our country the great host of wood-creatures, the bears,

squirrels, the wood-birds and insects, can no longer maintain

themselves, and grow rare and disappear. Man often also influences the

status of a species by checking its increase either by actual

slaughter, as with the bison and passenger-pigeon, or by making

adverse changes in its environment, as by destroying forests, or

putting the plains under cultivation.

In the discussion of "species-forming" (see p. 408) it was shown that

adaptation may lead to the altering of species, and to the formation

of new ones (under the influence of natural selection). With the

gradual change of conditions, or with the facing of new conditions

because of an unusual migration to or invasion of new territory, those

individuals of the species exposed to the new conditions must adapt

themselves in structure and habit in order to meet successfully the

new demands. By the cumulative action of natural selection these

adaptive changes are emphasized; and this emphasis may come to be so

pronounced that the part of the species represented in this newly

acquired territory, if isolated from the original stock, is so altered

as to be quite distinct in appearance from the old. If these changed

individuals are also physiologically distinct from the old stock, i.e.

are unable to mate with them, a new species is established. As already

mentioned, the peopling of islands from mainlands is an excellent and

readily observable example of the phenomena referred to in the third

law of distribution.

FOOTNOTE:

[20] Jordan and Kellogg's "Animal Life," 1900, p. 274.

APPENDICES

EQUIPMENT AND METHODS

APPENDIX I

EQUIPMENT AND NOTES OF PUPILS

=Equipment of pupils.=--Each pupil should have a laboratory note-book

of about 8 × 10 inches, opening at the end, in which both drawings and

notes can be made. The paper should be unruled and of good quality

(not too soft). Each pupil should have also instruments of his own as

follows: scalpel, pair of small scissors, spring forceps, pair of

dissecting-needles, small glass pipette, and paper of ribbon-pins for

pinning out specimens. The cost of this outfit need not exceed $1.00.

The laboratory should furnish him with a dissecting-dish and a

dissecting-microscope, or at least a lens.

=Laboratory drawings and notes.=--Each pupil should make the drawings

called for in the directions for the laboratory exercises. These

drawings should be in outline, and put in by pencil; the lines may be

inked over if preferred. Shading should be used sparingly, if at all.

Each drawing and all the organs and animal parts represented in it

should be fully named. See the anatomical plates in this book for

example. With such complete "labelling," little note-taking need be

done in connection with the dissections.

Notes should be made of any observations which cannot be represented

in the drawings; for example, on the behavior of the living animals.

All notes referring to matters of life-history should be dated.

=Field-observations and notes.=--Scattered through this book will be

found numerous suggestions for student field-work, for the observation

of the life-history and habits and conditions of animals in nature. As

explained in the Preface, the initiation and direction of such work

must be left to the teacher. But its importance both because of its

instructiveness and its interest is great. Pupils should not only be

incited to make individual observations whenever and wherever they

can, but the teacher should make little field-excursions with the

class or with parts of it at various times, to ponds or streams or

woods, and "show things" to all. The life-history and feeding-habits

of insects, the web-making of spiders, the flight, songs, nesting, and

care of young of birds, the haunts of fishes, the development of

frogs, toads, and salamanders, the home-building and feeding-habits of

squirrels, mice, and other familiar mammals are all (as has been

called attention to at proper places in the book) specially fit

subjects for field-observation.

Each pupil should keep a field note-book, recording from day to day,

under exact date, any observations he may make. Let the most trivial

things be noted; when referred to later in connection with other notes

they may not seem so trivial. The field note-book should be smaller than

the laboratory note- and drawing-book, small enough to be carried in the

pocket. Notes should be made on the spot of observation; do not wait to

get home. Sketches, even rough ones, may be advantageously put into the

book. Students with photographic cameras can do some very interesting

and valuable field-work in making photographs of animals, their nests

and favorite haunts. Such photographic work is very effectively used now

in the illustration of books about animals and plants (see the

reproductions of photographs in this book). If the class is making a

collection the collecting notes or data made in the field-books of the

different pupil collectors should all be transferred to a common "Notes

on Collections" book kept by the whole class.

APPENDIX II

LABORATORY EQUIPMENT AND METHODS

=Equipment of laboratory.=--The equipment of the laboratory or

classroom will, of necessity, depend upon the opportunities afforded

the teacher by the school officers to provide such facilities as

instruments, books, and charts. If dissections are to be seriously and

properly made, however, some equipment is indispensable. Flat-topped

tables, not over 30 inches high, a few compound microscopes (one is

much better than none), as many simple lenses, or, far better, simple

dissecting-microscopes, as there are students, dissecting-dishes, a

pair of bone-clippers, one injecting-syringe, a bunch of bristles,

water, a few simple reagents and some inexpensive glassware, as

slides, cover-glasses, watch-crystals, and fruit- or battery-jars for

live cages and aquaria, make up a sufficient equipment for good work.

Much can be done with less, and perhaps a little more with some

additional facilities.

The dissecting-pans should be of galvanized iron or tin, oblong, about

6 × 8 inches by 2 inches deep, with slightly flaring sides. If an iron

wire be run around the margin, and the margin bent back over it, it

will strengthen the dish, and make a broader and smoother edge for the

hands to rest on. Diagonally across the dish, about one-fourth inch

from the bottom, should run a thick wire. A layer of paraffin one-half

inch thick should cover the bottom. It should be poured in melted,

when the diagonal wire will be imbedded in it and will hold it in

place. Acids must not be put into the pan.

The reagents necessary are alcohol of 95 per cent and 85 per cent, and

formalin of 4 per cent (the formaldehyde sold by druggists is 40 per

cent and should be diluted ten times with water), these for preserving

material for dissection; chloroform for killing specimens; glycerin for

making temporary microscopic mounts, and 20 per cent nitric acid for

preparing specimens for study of the nervous system. In addition there

will be needed the few other materials mentioned in the following

paragraphs as necessary in the preparation of injecting-fluids, the

staining of fresh tissue and preserving by special methods.

A list of reference books desirable in the laboratory is appended as a

separate paragraph (see p. 454).

=Collecting and preparing material for use in the laboratory.=--As

directions have been given in the "technical notes" scattered through

the book for the collecting and preparing of all the various kinds of

animals chosen as subjects of the laboratory exercises, it will only be

necessary to give here directions for making certain special mixtures

and for the special preparation of specimens by injection, etc.

Specimens to be used for dissection should be kept in alcohol of 85 per

cent or in formalin of 4 per cent. Alcohol is better for the earthworm,

but for the other examples formalin is either better or as good, and as

it is much cheaper it may well be chosen for the general preservative.

_Methyl green_, a stain used for coloring fresh tissues. Dissolve the

methyl green powder in water, using about as much powder as the water

will take up. Add a few drops of acetic acid.

_Injecting-masses._--Injections are best made with preparations of

French gelatine, but white glue will answer most purposes. For fine

injection use a combination of the following: 1 part of a solution of

gelatine, 1 part to 4 parts of water; 1 part of a saturated solution of

lead acetate in water, and 1 part of a saturated solution of potassium

bichromate in water. A mixture of these when hot gives a beautiful

yellow injection-mass which, filtered, will pass through the finest

capillaries. For different colorings use dry paints, which come in

ultramarine blue, vermilion, and green. The gelatine should be

thoroughly soaked before the coloring-matter is added. A mistake is

generally made in using the injection-mass too thick. One part by weight

of gelatine to six or even more parts of water is a good proportion. The

gelatine as well as glue-masses should be made in a water-bath, which

consists of one dish placed within another outer one containing warm

water. The mass should be injected warm, _not hot_, after which the

injected specimen is to be placed in cold water until the injecting-mass

has set. Glue (the ordinary white kind) can be used for most injections

just as the gelatine was used, but should not be so much diluted. All

injection-masses should be filtered through a cloth before using.

_Preparing skeletons._--In general, skeletons are best cleaned by

boiling. After most of the flesh has been cut away the skeleton should

be boiled in a soap solution until the remaining parts of the muscles

are thoroughly softened. The soap solution is made of 2,000 c.c. of

water, preferably distilled, 12 grams of saltpetre, and 75 grams of

hard soap (white). Heat these until dissolved, then add 150 c.c. of

strong ammonia. This stock solution is mixed with four or five parts

of water, when the mixture is ready for use. The bones after boiling

are rinsed in cold water, brushed and picked clean, then left to dry

on a clean surface.

_Preserving anatomical preparations._--Many specimens worth keeping

will be found, and for them a solution known as Fischer's formula is

suggested as good, especially for brains. Fischer's formula is made up

as follows: 2,000 c.c. of water, 50 c.c. of formalin, 100 grams of

sodium chloride, and 15 grams of zinc chloride. These are mixed

together until thoroughly dissolved. Open preparations well before

placing them in the liquid and use about twenty times the volume of

the object to be preserved.

_To keep fresh dissections._--For materials which are dissected fresh

and must be kept over for several days in a fresh condition add a few

drops of carbolic acid to the water which covers them. Carbolized

water (2 per cent in water) will preserve a great many tissues for a

long time. Hearts will remain for years in a supple condition in this

solution.

_Obtaining marine animals, microscopic preparations, etc._--For

schools not on the seashore the marine animals such as starfishes,

etc., which are to be dissected or examined as examples of the

branches to which they belong must be obtained as preserved specimens

from dealers in such supplies. Among such dealers on the Atlantic

coast are the Marine Biological Laboratory, Woods Holl, Mass.; F. W.

Walmsley, Academy of Natural Sciences, Philadelphia, Pa.; and H. H.

and C. S. Brimley, Raleigh, N. C.; on the Pacific coast the Supply

Department, Hopkins Seaside Laboratory, Stanford University,

California. Ward's Natural Science Establishment, Rochester, N. Y.,

supplies almost any biological specimens asked for. This establishment

furnishes already made dissections and sets illustrating life-history

and metamorphosis. The few permanent microscopic preparations which

are mentioned in the book as desirable to have can be made by the

teacher if he has had any training in microscopical technic. If not,

they may be bought cheaply of such dealers in natural history

supplies as the Bausch & Lomb Optical Co., Rochester, N. Y.; the

Kny-Scheerer Co., 17 Park Place, New York City; Queen & Co., 1010

Chestnut Street, Philadelphia, Pa., and numerous others. From these

dealers also can be bought all of the laboratory supplies, such as

lenses, slides, cover-glasses, dissecting-scalpels, scissors and

needles, etc., mentioned in this book.

_Reference books._--Throughout the preceding chapters exact references

have been made to various books, as many of which as possible should

be in the school-library. Some of these references have been made with

special regard to the teacher, but most with special regard to the

pupil. All of the books referred to are included in the following

list. For the convenience of the prospective buyer, the names of the

publishers and prices of the books are appended. In buying books, it

is of course not necessary to order from the various publishers. A

list of the books desired may be handed to any book-dealer, who will

order them and who should in most cases be able to get them for a

little less than publisher's list prices.

=Baskett, J. N.= The Story of the Birds. 1899, D. Appleton & Co.

$0.65.

=Beddard, Frank.= Animal Coloration. 1892, Macmillan Co. $3.50.

---- Zoogeography. 1895, Macmillan Co. $1.60.

=Bendire, Chas.= Directions for Collecting, Preparing, and

Preserving Birds' Eggs and Nests. Distributed by U. S. National

Museum.

=Bird Lore=, an Illustrated Journal about Birds. Macmillan Co.

$1.00 a year.

=Cambridge Natural History=, Vols. V (Peripatus), $4.00, VI

(Insects), $3.50. Macmillan Co.

=Chapman, Frank.= Handbook of the Birds of Eastern North America.

1899. D. Appleton & Co. $3.00.

=Comstock, J. H.= Manual for the Study of Insects. 1897, Comstock

Publishing Co. $3.75.

---- Insect Life. 1901, D. Appleton & Co. $1.50.

---- =and Kellogg, V. L.= Elements of Insect Anatomy. 1901,

Comstock Publishing Co. $1.00.

=Cooke, W. W.= Bird Migration in the Mississippi Valley.

Distributed by the Division of Biological Survey, U. S. Dept.

Agric.

=Cowan, T. W.= Natural History of the Honey-bee. 1890, London:

Houlston. 1s. 6d.

=Coues, Elliott.= Key to North American Birds. 1890, Estes and

Lauriat. $7.50.

=Darwin, Chas.= The Formation of Vegetable Mold through the

action of Worms. D. Appleton & Co. $1.50.

---- Origin of Species. 1896, Caldwell. $0.75.

---- The Structure and Distribution of Coral Reefs. D. Appleton &

Co. $2.00.

---- Plants and Animals under Domestication. D. Appleton & Co.

=Davie, Oliver.= Methods in the Art of Taxidermy. 1894, Oliver

Davie & Co., Columbus, O. $10 net.

=Gage, S. H.= Life History of the Toad. Teacher's Leaflets No. 9,

April, 1898, prepared by College of Agriculture, Cornell

University, Ithaca, N. Y.

=Heilprin, A.= The Distribution of Animals. 1886, D. Appleton &

Co. $2.00.

=Hodge, C. F.= The Common Toad. Nature Study Leaflet, Biology

Series No. 1. 1898, published by C. H. Hodge, Worcester, Mass.

=Holland, W. J.= The Butterfly Book. 1899, Doubleday and McClure

Co. $3.00.

=Hornaday, W. T.= Taxidermy and Zoological Collecting. 1897,

Chas. Scribner's Sons. $2.50 net.

=Howell, W. H.= Dissection of the Dog. 1889, Henry Holt & Co.

$1.00.

=Huxley, T. H.= The Crayfish: an introduction to the Study of

Zoology. D. Appleton & Co. $1.75.

=Jordan, D. S.= Manual of Vertebrate Animals of the Northern

United States, 8th ed. 1899. A. C. McClurg & Co. $2.50.

---- =and Evermann, B. W.= Fishes of North and Middle America, 4

vols. 1898-1900, Distributed by U. S. National Museum.

---- =and Kellogg, V. L.= Animal Life. 1900, D. Appleton & Co.

$1.20.

=Lubbock, John.= Ants, Bees, and Wasps. 1882. D. Appleton & Co.

$2.00.

=Marshall, H. M., and Hurst, C. H.= Practical Biology, 5th ed. G.

P. Putnam's Sons. $3.50.

=Martin, H. W., and Moale, W. A.= Handbook of Vertebrate

Dissection, 3 parts. 1881, Macmillan Co.

Part 1. How to dissect a Chelonian (red-bellied slider terrapin);

Part 2. How to dissect a bird (pigeon);

Part 3. How to dissect a rodent (rat).

=McCook, Henry.= American Spiders and their Spinning Work, 3

vols. 1889-1893, H. C. McCook, Phila., Pa. $30.00.

=Miall, L. C.= The Natural History of Aquatic Insects. 1895,

Macmillan Co. $1.75.

=Parker, T. J.= A Course of Instruction in Zootomy. 1884,

Macmillan Co. $2.25.

---- Lessons in Elementary Biology. 1897, Macmillan Co. $2.65.

---- =and Haswell, W. A.= Textbook of Zoology, 2 vols. 1897,

Macmillan Co. $9.00.

=Peckham, George W. and E. J.= On the Instincts and Habits of the

Solitary Wasps. 1898, sold by Des Forges & Co., Milwaukee, Wis.

$2.00.

=Potts, E.= Fresh-water Sponges. 1887, Phil. Acad. of Sciences.

=Poulton, E. B.= The Colors of Animals. 1890, D. Appleton & Co.

$1.75.

=Reighard, J. E., and Jennings, H. S.= The Anatomy of the Cat.

1901, Henry Holt & Co. $4.00.

=Ridgway, R.= Directions for Collecting Birds. Distributed by U.

S. National Museum.

=Riverside Natural History=, 6 vols. Houghton, Mifflin & Co.

$30.00.

=Romanes, Geo.= Darwin and After Darwin, I. 1895-97, Open Court

Publishing Co.

=Scudder, S. H.= The Life of a Butterfly. 1893, Henry Holt & Co.

$1.00.

=Van Beneden, E.= Animal Parasites and Messmates. 1876, D.

Appleton & Co. $1.50.

=Wallace, A. R.= The Geographical Distribution of Animals. 1876,

Harper & Bros. $10.00.

=Wallace, A. R.= Island Life. 1881, Harper & Bros. $4.00.

APPENDIX III

REARING ANIMALS AND MAKING COLLECTIONS

Much good work in observing the behavior and life-history of some

kinds of animals can be done by keeping them alive in the schoolroom

under conditions simulating those to which they are exposed in nature.

The growth and development of frogs and toads from egg to adult, as

well as their feeding habits and general behavior, can all be observed

in the schoolroom as explained in Chapter XII. Harmless snakes are

easily kept in glass-covered boxes; snails and slugs are contented

dwellers indoors; certain fish live well in small aquaria, and many

other familiar forms can be kept alive under observation for a longer

or shorter time. But from the ease with which they are obtained and

cared for, the inexpensiveness of their live-cages, and the

interesting character of their life-history and general habits,

insects are, of all animals, the ones which specially commend

themselves for the schoolroom menagerie. In the technical notes in the

chapter (XXI) devoted to insects are numerous suggestions regarding

the obtaining and care of certain kinds of insects which may be reared

and studied to advantage in the schoolroom. In the following

paragraphs are given directions for making the necessary live-cages

and aquaria for these insects.

=Live-cages and aquaria.=--Prof. J. H. Comstock has so well described

the making of simple and inexpensive cages and aquaria in his book,

"Insect Life," that, with his permission, his account is quoted here.

_Live-cages._--"A good home-made cage can be built by fitting a pane of

glass into one side of an empty soap-box. A board, three or four inches

wide, should be fastened below the glass so as to admit of a layer of

soil being placed in the lower part of the cage, and the glass can be

made to slide, so as to serve as a door (fig. 166). The glass should fit

closely when shut, to prevent the escape of the insects.

[Illustration: FIG. 166.--Soap-box breeding-cage for insects. (From

Jenkins and Kellogg.)]

"In rearing caterpillars and other leaf-eating larvæ, branches of the

food-plant should be stuck into bottles or cans which are filled with

sand saturated with water. By keeping the sand wet the plants can be

kept fresh longer than in water alone, and the danger of the larvæ

being drowned is avoided by the use of sand.

"Many larvæ when full-grown enter the ground to pass the pupal state;

on this account a layer of loose soil should be kept in the bottom of

a breeding-cage. This soil should not be allowed to become dry,

neither should it be soaked with water. If the soil is too dry the

pupæ will not mature, or if they do so the wings will not expand

fully; if the soil is too damp the pupæ are liable to be drowned or to

be killed by mold.

"It is often necessary to keep pupæ over winter, for a large

proportion of insects pass the winter in the pupal state. Hibernating

pupæ may be left in the breeding-cages or removed and packed in moss

in small boxes. Great care should be taken to keep moist the soil in

the breeding-cages, or the moss if that be used. The cages or boxes

containing the pupæ should be stored in a cool cellar, or in an

unheated room, or in a large box placed out of doors where the sun

cannot strike it. Low temperature is not so much to be feared as great

and frequent changes of temperature.

"Hibernating pupæ can be kept in a warm room if care be taken to keep

them moist, but under such treatment the mature insects are apt to

emerge in midwinter.

[Illustration: FIG. 167.--Lamp-chimney and flower-pot breeding-cage

for insects. (From Jenkins and Kellogg.)]

"An excellent breeding-cage is represented by fig. 167. It is made by

combining a flower-pot and a lantern-globe. When practicable, the

food-plant of the insects to be bred is planted in the flower-pot; in

other cases a bottle or tin can filled with wet sand is sunk into the

soil in the flower-pot, and the stems of the plant are stuck into this

wet sand. The top of the lantern-globe is covered with Swiss muslin.

These breeding-cages are inexpensive, and especially so when the pots

and globes are bought in considerable quantities. A modification of

this style of breeding-cage that is used by the writer differs only in

that large glass cylinders take the place of the lantern-globes. These

cylinders were made especially for us by a manufacturer of glass, and

cost from six to eight dollars per dozen, according to size, when made

in lots of fifty.

"When the transformation of small insects or of a small number of

larger ones are to be studied, a convenient cage can be made by

combining a large lamp-chimney with a small flower-pot.

"_The root-cage._--For the study of insects that infest the roots of

plants, the writer has devised a special form of breeding-cage known as

the root-cage. In its simplest form this cage consists of a frame

holding two plates of glass in a vertical position and only a short

distance apart. The space between the plates of glass is filled with

soil in which seeds are planted or small plants set. The width of the

space between the plates of glass depends on the width of two strips of

wood placed between them, one at each end, and should be only wide

enough to allow the insects under observation to move freely through the

soil. If it is too wide the insects will be able to conceal themselves.

Immediately outside of each glass there is a piece of blackened zinc

which slips into grooves in the ends of the cage, and which can be

easily removed when it is desired to observe the insects in the soil.

"_Aquaria._--For the breeding of aquatic insects aquaria are needed.

As the ordinary rectangular aquaria are expensive and are liable to

leak we use glass vessels instead.

"Small aquaria can be made of jelly-tumblers, glass finger-bowls, and

glass fruit-cans, and larger aquaria can be obtained of dealers. A

good substitute for these is what is known as a battery-jar (fig.

168). There are several sizes of these, which can be obtained of most

dealers in scientific apparatus.

"To prepare an aquarium, place in the jar a layer of sand; plant some

water-plants in this sand, cover the sand with a layer of gravel or

small stones, and then add the required amount of water carefully, so

as not to disturb the plants or to roil the water unduly. The growing

plants will keep the water in good condition for aquatic animal life,

and render changing of the water unnecessary, if the animals in it

live naturally in quiet water. Among the more available plants for use

in aquaria are the following:

"Waterweed, _Elodea canadensis_.

"Bladderwort, _Utricularia_ (several species).

"Water-starwort, _Callitriche_ (several species).

"Watercress, _Nasturtium officinale_.

"Stoneworts, _Chara and Nitella_ (several species of each).

"Frog-spittle or water-silk, _Spirogyra_.

"A small quantity of duckweed, _Lemna_, placed on the surface of the

water adds to the beauty of an aquarium.

[Illustration: FIG. 168.--Battery-jar aquarium. (From Jenkins and

Kellogg.)]

"When it is necessary to add water to an aquarium on account of loss

by evaporation, rain water should be used to prevent an undue

accumulation of the mineral-water held in solution in other water."

=Making collections.=--Much is to be learned about animals by

"collecting" them. But the collecting should be done chiefly with the

idea of learning about the animals rather than with the notion of

getting as many specimens as possible. To collect, it is necessary to

find the animals alive; one learns thus their haunts, their local

distribution, and something of their habits, while by continued work

one comes to know how many and what different kinds or species of each

group being collected occur in the region collected over. Collecting

requires the sacrifice of life, however, and this will always be kept

well in mind by the humane teacher and pupil. Where one set of

specimens will do, no more should be collected. The author believes

that high-school work in this line should be almost exclusively

limited to the building up of a common school collection. Let a single

set of specimens be brought together by the combined efforts of all

the members of the class, and let it be well housed and cared for

permanently. Each succeeding class will add to it; it may come in time

to be a really representative exhibition of the local fauna.

The high-school collection should include not only adult specimens of

the various kinds of animals, forming a systematic collection, as it

is called, but also all kinds of specimens which illustrate the

structure and habits of the animals in question and which will

constitute a so-called biological collection. Specimens of the eggs

and all immature stages; dissections preserved in alcohol or formalin

showing the external and internal anatomy; nests, cocoons, and all

specimens showing the work and industries of the various animals; in

short, any specimen of the animal itself in embryonic or postembryonic

condition, or any parts of the animal, or anything illustrating what

the animal does or how it lives, all these should be collected as

assiduously as the adult individuals. Each specimen in the collection

should be labelled with the name of the animal, the date, and

locality, and the name of the collector, with any particular

information which will make it more instructive. If such special data

are too voluminous for a label, they should be written in a general

note-book called "Notes on Collections" (kept in the schoolroom with

the collection), the specimen and corresponding data being given a

common number so that their association may be recognized. In the

following paragraphs are given brief directions for catching, pinning

up, and caring for insects, for making skins of birds and mammals, and

for the alcoholic preservation of other kinds of animals.

_Insects._--For catching insects there are needed a net, a

killing-bottle, a few small vials of alcohol, and a few small boxes to

carry home live specimens, cocoons, galls, etc. For preparing and

preserving the insects there are needed insect-pins, cork- or pith-lined

drawers or boxes, and small wide-mouthed bottles of alcohol.

[Illustration: FIG. 169.--Insect killing-bottle; cyanide of potassium

at bottom, covered with plaster of Paris. (From Jenkins and Kellogg.)]

The net, about 2 feet deep, tapering and rounded at its lower end, is

made of cheesecloth or bobinet (not mosquito-netting, which is too

frail), attached to a ring, one foot in diameter, of No. 3 galvanized

iron wire, which in turn is fitted into a light wooden or cane handle

about three and a half feet long.

The killing-bottle (fig. 169) is prepared by putting a few small lumps

(about a teaspoonful) of cyanide of potassium into the bottom of a

wide-mouthed bottle holding about four ounces, and covering this

cyanide with wet plaster of Paris. When the plaster sets it will hold

the cyanide in place, and allow the fumes given off by its gradual

volatilization to fill the bottle. Insects dropped into it will be

killed in from two or three to ten minutes. Keep a little tissue paper

in the bottle to soak up moisture and to prevent the specimens from

rubbing. Also keep the bottle well corked. Label it "Poison," and do

not breathe the fumes (hydrocyanic gas). Insects may be left in it

over night without injury to them.

Butterflies or dragon-flies too large to drop into the killing-bottle

may be killed by dropping a little chloroform or benzine on a piece of

cotton, to be placed in a tight box with them. Larvæ (caterpillars,

grubs, etc.) and pupæ (chrysalids) should be dropped into the vials of

alcohol.

In collecting, visit flowers, sweep the net back and forth over the

small flowers and grasses of meadows and pastures, look under stones,

break up old logs and stumps, poke about decaying matter, jar and

shake small trees and shrubs, and visit ponds and streams. Many

insects can be collected in summer at night about electric lights, or

a lamp by an open window.

When the insects are brought home or to the schoolroom they must be

"pinned up." Buy insect-pins, long, slender, small-headed, sharp-pointed

pins, of a dealer in naturalists' supplies (see p. 453). These pins cost

ten cents a hundred. Order Klaeger pins, No. 3, or Carlsbaeder pins, No.

5. These are the most useful sizes. For larger pins order Klaeger No. 5

(Carlsbaeder No. 8); for smaller order Klaeger No. 1 (Carlsbaeder No.

2). Pin each insect straight down through the thorax (fig. 170) (except

beetles, which pin through the right wing-cover near the middle of the

body). On each pin below the insect place a small label with date and

locality of capture. Insects too small to be pinned may be gummed on to

small slips of cardboard, which should be then pinned up. Keep the

insects in drawers or boxes lined on the bottom with a thin layer of

cork, or pith of some kind. (Corn-pith can be used; also in the West,

the pith of the flowering stalk of the century plant.) The cheapest

insect-boxes and very good ones, too, are cigar-boxes. But unless well

looked after they let in tiny live insects which feed on the dead

specimens. For a permanent collection, therefore, it will be necessary

to have made some tight boxes or drawers. Glass-topped ones are best, so

that the specimens may be examined without opening them. A "moth-ball"

(naphthaline) fastened in one corner of the box will help keep out the

marauding insects.

[Illustration: FIG. 170.--Insect properly "pinned up." (From Jenkins

and Kellogg.)]

Butterflies, dragon-flies, and other larger and beautiful-winged

insects should be "spread," that is, should be allowed to dry with

wings expanded. To do this spreading- or setting-boards (figs. 171 and

172) are necessary. Such a board consists of two strips of wood

fastened a short distance apart so as to leave between them a groove

for the body of the insect, and upon which the wings are held in

position until the insect is dry. A narrow strip of pith or cork

should be fastened to the lower side of the two strips of wood,

closing the groove below. Into this cork is thrust the pin on which

the insect is mounted. Another strip of wood is fastened to the lower

sides of the cleats to which the two strips are nailed. This serves as

a bottom and protects the points of the pins which project through the

piece of cork. The wings are held down, after having been outspread

with the hinder margins of the fore wings about at right angles to the

body, by strips of paper pinned down over them.

"Soft specimens" such as insect larvæ, myriapods, and spiders should

be preserved in bottles of alcohol (85 per cent). Nests, galls, stems,

and leaves partly eaten by insects, and other dry specimens can be

kept in small pasteboard boxes.

For a good and full account of insect-collecting and preserving, with

directions for making insect-cases, etc., see Comstock's "Insect

Life," pp. 284-314.