[Illustration: FIG. 88.--LENGTHWISE SECT_First course in biology

_c_, heart; _Ac_, artery to head; _Aa_, artery to abdomen; _Km_,

stomach; _D_, intestine; _L_, liver; _T_, spermary; _Go_, opening of

sperm duct; _G_, brain; _N_, nerve chain.]

Find the pair of _antennules_, or small feelers. Are their divisions

like or unlike each other? Compare the length of the antennules and the

antennæ. Compare the flexibility of the antennæ with that of the other

appendages.

Observe the position of the _eyes_ (Figs. 81, 88). How long are the

eyestalks? Is the stalk flexible or stiff? Touch the eye. Where is the

joint which enables the stalk to move? Is the outer covering of the

eye hard or soft? A mounted preparation of the transparent covering

(cornea) of the eye, seen with lower power of microscope, reveals that

the cornea is made up of many divisions, called facets. Each facet is

the front of a very small eye, hundreds of which make up the whole eye,

which is therefore called a compound eye. The elongated openings to the

_ear sacs_ are located each on the upper side of the base of a small

feeler just below the eye.

=Respiratory System.=--The respiratory organs are gills located on

each side of the thorax in a space between the carapace and body (Fig.

87). The gills are white, curved, and feathery. Is the front gill the

largest or the smallest? The gills overlap each other; which is the

outermost gill? On the second maxilla is a thin, doubly curved plate

called a gill bailer (Fig. 85). The second maxilla is so placed that

the gill bailer comes at the front end of the gill chamber. The bailer

paddles continually, bringing the water forward out of the gill.

The gills are attached below at the base of the legs. Are the gills

thick or thin? How far upward do they go? Does the backward motion in

swimming aid or hinder the passage of the water through the gills? Does

a crawfish, when at rest on the bottom of a stream, have its head up or

down stream? Why?

=Openings.=--The slitlike _vent_ is on the under side of the telson

(Figs. 82, 88). The _mouth_ is on the under side of the thorax behind

the mandibles. At the base of the long antennæ are the openings from

the _green glands_, two glands in the head which serve as kidneys (Fig.

89). The openings of the _reproductive organs_ are on the third pair of

legs in the female, and the fifth pair of legs in the male (Fig. 88).

The eggs are carried on the swimmerets.

[Illustration: FIG. 89.--Level lengthwise section showing

_h_, heart.

_d_, green gland.

_le_, liver.

_kie_, gills.

_kh_, gill cavity.

_ma_, stomach.

(After Huxley.)]

=Internal Structure.=--SUGGESTIONS. If studied by dissection, it will

be necessary to have several crawfish for each pupil, one for gaining

general knowledge, and others for studying the systems in detail.

Specimens should have lain in alcohol for several days.

[Illustration: FIG. 90.--SECTION OF CRAWFISH showing stomach _s_, liver

_li_, and vent _a_.]

=The Food Tube.=--Is the stomach in the head portion of the

cephalothorax or in the thoracic portion? (Figs. 88, 89). Is the

stomach large or small? What is its general shape? Does the gullet

lead upward or backward? Is it long or short? (Fig. 88.) The mid

tube, which is the next portion of the food tube, is smaller than the

stomach. On each side of it are openings from the bile ducts which

bring the secretion from the digestive gland, sometimes called the

liver. Does this gland extend the whole length of the thorax? Is it

near the floor or the top of the cavity? The third and last portion

of the food tube is the intestine. It extends from the thorax to

the vent. Is it large or small? Straight or curved? The powerful

flexor muscles of the tail lie in the abdomen below the intestines.

Compare the size of these muscles with the extensor muscle above the

intestine (Fig. 90). Why this difference? Does the food tube extend

into the telson? Locate the vent (Fig. 90).

=The Circulation.=--The blood is a liquid containing _white

corpuscles_. It lacks red corpuscles and is colorless. The heart is

in the upper part of the thorax. It is surrounded by a large, thin

bag, and thus it is in a chamber (called the _pericardial sinus_).

The blood from the pulmonary veins enters this sinus before it enters

the heart. The origin of this pericardial sinus by the fusing of

veins is shown in Fig. 130. Does one artery, or do several arteries,

leave the heart? There is a larger dorsal artery lying on the

intestine and passing back to the telson; there are three arteries

passing forward close to the dorsal surface (Figs. 89, 91). One large

artery (the sternal) passes directly downward (Figs. 88, 91), and

sends a branch forward and another backward near the ventral surface.

The openings into the heart from the sinus have valvular lips which

prevent a backward flow of blood into the sinus. Hence, when the

heart contracts, the blood is sent out into the several arteries. The

arteries take a supply of fresh blood to the eyes, stomach, muscles,

liver, and the various organs. After it has given oxygen to the

several organs and taken up carbon dioxid, it returns by veins to

pass through the gills on each side, where it gives out the useless

gas and takes up oxygen from the water. It is then led upward by

veins into the pericardial sinus again.

A _double nerve chain_ of ganglia supplies nerve force to the various

nerves (Fig. 92). This main nerve chain lies along the ventral

surface below the food tube (Fig. 90), except one pair of ganglia

which lie above the esophagus or gullet (Fig. 88), and are called the

supra-esophageal ganglia, or brain.

[Illustration: FIG. 91.--Showing heart and main blood vessels.]

[Illustration: FIG. 92.]

=Crustacea.=--Because of the limy crust which covers the crawfish and

its kindred, they are placed in the class called _Crustacea_.

[Illustration: FIG. 93.--CRAB FROM BELOW.]

[Illustration: FIG. 94.--HERMIT CRAB, using shell of sea snail for a

house.]

=Decapods.=--All crustacea which have ten feet belong in the order

called decap′oda (ten-footed). This order includes the crabs, lobsters,

shrimp, etc. The crabs and lobsters are of considerable importance

because of use as food. Small boys sometimes catch crawfish, and in

some instances are known to cook and eat them for amusement, the only

part cooked being the muscular tail. The crab’s tail is small and flat

and held under the body (Fig. 93).

[Illustration: FIG. 95.--DEVELOPMENT OF A CRAB.

_a_, nauplius just after hatching; _b_, _c_, _d_, zoëa; _e_, megalops;

_f_, adult.

=Question:= Which stage is most like a crayfish? Compare with

metamorphoses of insects.]

Since the limy covering to serve the purpose of protection is not soft

enough to be alive and growing, it is evident that the crustacea are

hampered in their growth by their crusty covering. During the first

year the crawfish sheds its covering, or =molts= three times, and once

each year thereafter. It grows very fast for a few days just after

molting, while the covering is soft and extensible. Since it is at

the mercy of birds, fish, and other enemies while in this soft and

defenseless condition, it stays hidden until the covering hardens.

Hence it cannot eat much, but probably by the absorption of water the

tissues grow; that is, enlarge. In the intervening periods, when growth

is impossible, it develops; that is, the tissues and organs change in

structure and become stronger. “Soft-shelled crab” is a popular dish,

but there is no species by that name, this being only a crab just after

molting which has been found by fishermen in spite of its hiding.

=General Questions.=--How do crawfish choose their food? How long

can they live out of water? Why do their gills remain moist out of

water longer than a fish? How do they breathe out of water? Are

they courageous or cowardly animals? When they lose appendages when

fighting or molting, they are readily reproduced, but the part molts

several times in regaining its size. Have you seen crawfish with one

claw smaller than the other? Explain.

Compare the crawfish and crab (Figs. 81, 93, and 95) in the following

particulars: shape, body, eyes, legs, abdomen, habitat, movement.

KEY TO THE FOUR CLASSES IN BRANCH ARTHROPODS

1. INSECTS 3 body divisions, 6 legs

2. ARACHNIDS 2 body divisions, 8 legs

3. MYRIAPODS many body divisions, many legs

4. CRUSTACEANS gill breathers, skeleton (external) limy

By the aid of the key and of figures 96-105, classify the following

Arthropods: tick, thousand-leg centipede, king crab, pill bug,

spider, scorpion, beetle.

[Illustration: FIG. 96.--PILL BUG.]

[Illustration: FIG. 97.--LADY BEETLE.]

[Illustration: FIG. 98.--SCORPION.]

[Illustration: FIG. 99.--TICK before and after feeding.]

[Illustration: FIG. 100.--CENTIPEDE.]

[Illustration: FIG. 101.--ONE SEGMENT OF CENTIPEDE with one pair of

legs.]

[Illustration: FIG. 102.--ONE SEGMENT OF THOUSAND LEGS with two pairs

of legs.]

[Illustration: FIG. 103.--THOUSAND LEGS.]

[Illustration: FIG. 104.--A SPIDER.]

[Illustration: FIG. 105.--KING CRAB.]

=Illustrated Study.= CLASSIFICATION OF ARTHROPODS. Key on p. 61.

CHAPTER VIII

INSECTS

THE GRASSHOPPER

SUGGESTIONS.--Collect grasshoppers, both young and full-grown, and

keep alive in broad bottles or tumblers and feed on fresh grass or

lettuce. When handling a live grasshopper, never hold it by its

legs, as the joints are weak. To keep them for some time and observe

their molts, place sod in the bottom of a box and cover the box with

mosquito netting or wire gauze.

What is the =general shape= of its body? (Fig. 106.) Where is the body

thickest? Is it bilaterally symmetrical, that is, are the two sides of

the body alike? Is the _skeleton_, or hard part of the body, internal

or external? Is the skeleton as stiff and thick as that of a crawfish?

What is the length of your specimen? Its color? Why does it have this

coloration? In what ways does the grasshopper resemble the crawfish?

Differ from it?

[Illustration: FIG. 106.--A GRASSHOPPER.]

=The Three Regions of the Body.=--The body of the grasshopper is

divided into three regions,--the _head_, _thorax_, and _abdomen_.

Which of these three divisions has no distinct subdivisions? The body

of the grasshopper, like that of the earthworm, is made of _ringlike

segments_. Are the segments most distinct in the head, thorax, or

abdomen? Which region is longest? Shortest? Strongest? Why? Which

region bears the chief sense organs? The appendages for taking food?

The locomotory appendages? Which division of the body is most active in

breathing?

=The Abdomen.=--About how many segments or rings in the abdomen? Do

all grasshoppers have the same number of rings? (Answer for different

species and different individuals of the same species.) The first

segment and the last two are incomplete rings. Does the flexibility of

the abdomen reside in the rings, or the joints between the rings? Is

there merely a thin, soft line between the rings, or is there a fold of

the covering? Does one ring slip into the ring before it or behind it

when the abdomen is bent?

As the grasshopper =breathes=, does each ring enlarge and diminish in

size? Each _ring is divided into two parts_ by folds. Does the upper

half-ring overlap the lower half-ring, or the reverse? With magnifying

glass, find a small slit, called a _spiracle_, or breathing hole, on

each side of each ring just above the side groove (Fig. 106). A tube

leads from each spiracle. While the air is being taken in, do the

two portions of the rings move farther apart? When they are brought

together again, what must be the effect? In pumping the air, the

abdomen may be said to work like a bellows. Bellows usually have folds

to allow motion. Is the comparison correct?

How many times in a minute does the grasshopper take in air? If it

is made to hop vigorously around the room and the breathing is again

timed, is there any change?

[Illustration: FIG. 107.--A GRASSHOPPER DISSECTED.]

Find the =ears= on the front wall of the _first abdominal ring_ (Fig.

107). They may be seen by slightly pressing the abdomen so as to widen

the chink between it and the thorax. The ears are merely glistening,

transparent _membranes_, oval in form. A _nerve_ leads from the inner

surface of each membrane. State any advantage or disadvantage in having

the ears located where they are.

=Ovipositor.=--If the specimen is a female, it has an egg-placer or

ovipositor, consisting of _four blunt projections_ at the end of the

abdomen (Fig. 107). If it is a male, there are only two appendages.

These are above the end of the abdomen, and smaller than the parts of

the ovipositor. Females are larger and more abundant than males. In

laying the eggs, the four blunt points are brought tightly together and

then forced into the ground and opened (Fig. 108). By repeating this, a

pit is made almost as deep as the abdomen is long. What sex is shown in

Fig. 106? Fig. 107?

=Draw= a side view of the grasshopper.

[Illustration: FIG. 108.--GRASSHOPPER LAYING EGGS. (Riley.)]

=Thorax.=--This, the middle portion of the body, consists of _three

segments_ or rings (Fig. 107). Is the division between the rings most

apparent above or below? Which two of the three rings are more closely

united?

The front ring (_prothorax_) of the thorax has no rings. Is it larger

above or below? Does it look more like a collar or a cape? (Fig. 106.)

A spiracle is found on the second ring (_mesothorax_, or middle thorax)

just above the second pair of legs. There is another in the soft skin

between the prothorax and mesothorax just under the large cape or

collar. The last ring of the thorax is called the _metathorax_ (rear

thorax).

How many =legs= are attached to each ring of the thorax? Can a

grasshopper walk? Run? Climb? Jump? Fly? Do any of the legs set

forward? (See Fig. 106.) Outward? Backward? Can you give reasons for

the position of each pair? (Suggestion: What is the use of each pair?)

If an organ is modified so that it is suited to serve some particular

purpose or function, it is said to be _specialized_. Are any of the

legs specialized so that they serve for a different purpose than the

other legs?

The leg of a grasshopper (as of all insects) is said to have _five

parts_, all the small parts after the first four parts being counted

as one part and called the foot. Are all the legs similar, that is, do

the short and long joints in all come in the same order? Numbered in

order from the body, which joint of the leg is the largest,--the first,

second, third, or fourth? Which joint is the shortest? The slenderest?

Which joint has a number of sharp points or spines on it? Find by

experiment whether these spines are of use in walking (Fig. 106).

Jumping? Climbing? In what order are the legs used in walking? How many

legs support the body at each step?

[Illustration: FIG. 109.--HOW A GRASSHOPPER WALKS.]

[Illustration: FIG. 110.--HOW A SPIDER WALKS.]

All animals that have ears have ways of communicating by =sounds=. Why

would it be impossible for the grasshopper to have a _voice_, even if

it had vocal cords in its throat? The male grasshoppers of many species

make a =chirping=, or stridulation, by rubbing the wing against the

leg. Look on the inner side (why not outer side?) of the largest joint

of the hind leg for a _row of small spines_ visible with the aid of a

hand lens (Fig. 111). The sound is produced by the outer wings rubbing

against the spines. Have you noticed whether the sound is produced

while the insect is still or in motion? Why? The male grasshoppers of

some species, instead of having spines, rub the under side of the front

wing on the upper side of the hind wing.

[Illustration: FIG. 111.--_A_, ROW OF SPINES, _z_, used in chirping.

_B_, the same more enlarged.]

=Wings.=--To what is the first pair of wings attached? The second pair?

Why are the wings not attached to the prothorax? Why are the wings

attached so near the dorsal line of the body? Why are the second and

third rings of the thorax more solidly joined than the first and second

rings?

Compare the first and second pairs of wings in shape, size, color,

thickness, and use (Fig. 112). How are the second wings folded so as to

go under the first wings? About how many folds in each?

[Illustration: FIG. 112.--GRASSHOPPER IN FLIGHT.]

=Draw= a hind wing opened out.

=Head.=--What is the shape of the head viewed from the front, the side,

and above? _Make sketches._ What can you say of a neck? Is the head

movable in all directions?

What is the position of the large =eyes=? Like the eyes of the

crawfish, they are _compound, with many facets_. But the grasshopper

has also _three simple eyes_, situated one in the middle of the

forehead and one just above each antenna. They are too small to be seen

without a hand lens. How does the grasshopper’s range of vision compare

with that of the crawfish?

Are the =antennæ= flexible? What is their shape? Position? Are they

segmented? Touch an antenna, a wing, a leg, and the abdomen in

succession. Which seems to be the most sensitive to touch? The antennæ

are for feeling; in some species of insects they are also the organs of

hearing.

[Illustration: FIG. 113.]

The =mouth parts= of a grasshopper are highly specialized. They should

be compared with the mouth parts of a beetle shown in Fig. 113, since

the mouth parts of these two insects correspond closely. If the

grasshopper is fed with a blade of fresh grass, the function of each

mouth part may be plainly seen. It is almost impossible to understand

these functions by studying a dead specimen, but a fresh specimen is

much better than a dry one.

[Illustration: FIG. 114.--_a_, FOOD TUBE OF BEETLE.

_b_, gizzard; _d_, intestine; _c_, biliary vessels. See Fig. 127.]

The upper lip, or _labrum_, is seen in front. Is it tapering or

expanded? In what direction is it movable? The dark pointed biting jaws

(_mandibles_) are next. Are they curved or straight? Sharp or blunt

pointed? Notched or smooth? Do they work up and down, or sideways? The

holding jaws (_maxillæ_), each with two jaw fingers (_maxillary palpi_)

are behind the chewing jaws. Why? The lower lip (_labium_) has a pair

of lip fingers (_labial palpi_) upon it. The brown tongue, usually

bathed in saliva, is seen in the lower part of the mouth. Since the

grasshopper has no lips, or any way of producing suction, it must lap

the dew in drinking. Does it merely break off bits of a grass blade, or

does it chew?

The heart, circulation, nervous system, digestive and respiratory

organs of the grasshopper agree mainly with the general description of

the organs of insects given in the next section.

=Microscopic Objects.=--These may be bought ready mounted, or may be

examined fresh. A portion of the covering of the large eye may be cut

off and the dark layer on the inside of the covering scraped off to

make it transparent. What is the shape of the facets? Can you make any

estimate of their number? A portion of the transparent hind wing may be

used, and the “veins” in it studied. A thin bit of an abdominal segment

containing a spiracle will show the structure of these important organs.

[Illustration: FIG. 115.--EGG AND MOLTS OF A GRASSHOPPER.]

=Growth of the Grasshopper.=--Some species hibernate in sheltered

places and lay eggs in the spring, but adult species are scarce at

that season. Most species lay the eggs in the fall; these withstand

the cold and hatch out in the spring. Those hatched from one set of

eggs sometimes stay together for a few days. They eat voraciously, and

as they grow, the soft skin becomes hardened by the deposit of horny

substance called chitin. This prevents further growth until the insect

molts, the skin first splitting above the prothorax. After hatching,

there are five successive periods of growth. At which molt do the very

short wings first appear? (Fig. 115.) After the last molt the animal is

complete, and changes no more in size for the rest of its life. There

has been an attempt among writers to restrict the term grasshopper

to the long-winged, slender species, and to call the shorter winged,

stouter species locusts according to old English usage.

[Illustration: FIG. 116.--COCKROACH.]

[Illustration: FIG. 117.--PRAYING MANTIS, or devil’s horse.]

[Illustration: FIG. 118.--CRICKET.]

[Illustration: FIG. 119.--MOLE CRICKET.]

=Economic Importance of Grasshoppers.=--Great injury is often done to

vegetation by grasshoppers; however, the millions of tiny but ravenous

eaters hatched in early spring are usually soon thinned out by the

birds. The migratory locusts constitute a plague when they appear,

and they have done so since ancient times. The Rocky Mountain locusts

flying eastward have darkened the sky, and where they settled to the

earth ate almost every green thing. In 1874-5 they produced almost

a famine in Kansas, Nebraska, and other Western states. The young

hatched away from the mountains were not healthy, and died prematurely,

and their devastations came to an end. Of course the migrations may

occur again. Packard calculates that the farmers of the West lost

$200,000,000 because of their ravages in 1874-5.

[Illustration: FIG. 120.--FRONT LEG OF MOLE CRICKET. × 3.]

The _cockroaches_ (Fig. 116), =kindred of the grasshoppers=, are

household pests that have migrated almost everywhere that ships go.

The _praying mantis_ (Fig. 117), or _devil’s horse_, also belongs to

this order. It is beneficial, since it destroys other insects. Which of

its legs are specialized? The _walking stick_ (Fig. 121) and _cricket_

(Fig. 118), like most members of the order, are vegetarian.

[Illustration: FIG. 121.--FOUR WALKING STICK INSECTS.]

Are grasshoppers more common in fields and meadows, or in wooded

places? How many different colors have you seen on grasshoppers? Which

colors are most common?

Grasshoppers are very scarce in Europe as they love dry, warm

countries. Why do locusts migrate? Give an instance in ancient times.

How long do most grasshoppers live? Does a grasshopper spread its wings

before it flies? Does it jump and fly together? Can it select the place

for alighting?

NOTE TO TEACHER.--=Field work in Zoology= should be systematic.

Every trip has a definite region and definite line of study in view,

but every animal seen should be noted. The habitat, adaptation by

structure and habits to the environment, relations to other animals,

classification of animals seen, should be some of the ideas guiding

the study. The excursions may be divided somewhat as follows,

according as opportunities offer: Upland woods, lowland woods, upland

pastures, fields, swamps, a fresh-water lake, a pond, lower sea

beach, higher sea beach, sand hills along shore, roadside, garden,

haunts of birds, insect visits to flowers, ground insects, insects in

logs.

An alphabetical letter file may be used for filing individual field

observations. These should be placed before the class orally or in

writing. If accepted as reliable (repeated and revised if necessary),

the observations should be filed away and credit given the student on

a regular scale. Thus will grading and marks be placed to encourage

intelligent study of nature rather than book or laboratory cram. One

per cent to be added to the final grade may be credited for every

species of pupa, every rare insect (with an observed fact as to its

habits) brought in, every bird migration observed, every instance

of protective coloration, mimicry (p. 146), outwitting of enemy,

instance of injurious insects, and how to combat them, etc. Sharp

eyes and clear reasoning will then count as much on school grades as

a memory for words or mechanical following of laboratory directions.

On scale of 100, class work = 50, examination = 25, field work = 25.

=Collecting Insects.=--In cities and towns insects, varying with the

season, are attracted by electric lights. Beetles and bugs will be

found under the lights, moths on posts near the lights, grasshoppers

and crickets and other insects in the grass near by. A lamp placed

by a window brings many specimens. In the woods and in rocky places

insects are found under logs and stones, and under the bark of dead

trees. In open places, prairies, meadows, and old fields with grass

and flowers, it will be easy to find grasshoppers, butterflies, and

some beetles. Ponds and streams are usually rich in animal forms,

such as bugs and beetles, which swim on or under the surface, and

larvæ of dragon flies crawling on the bottom. Dragon flies and other

insects that lay eggs on the water are found flying in the air above.

(In the spring, newly hatched crawfish, tadpoles, and the eggs of

frogs and toads should also be collected, if found.) Moths may be

caught at night by daubing molasses or sirup made from brown sugar

upon the trunks of several trees, and visiting the trees at intervals

with a lantern.

An insect net for catching butterflies and for dredging ponds may

be made by bending a stout wire into a circle one foot in diameter,

leaving enough straight wire to fasten with staples on an old

broomstick. To the frame is fastened a flour sack, or cone made of a

piece of mosquito netting.

Butterflies and moths should be promptly killed, or they will beat

their wings to pieces. The quickest method is by dropping several

drops of gasoline upon the ventral (under) side of the thorax and

abdomen. (Caution: Gasoline should never be used near an open fire,

or lamp, as explosions and deaths result from the flame being led

through the gasoline-saturated air to the vessel containing it.)

A cigar box and a bottle with a notched cork may be used for holding

specimens. Cigar boxes may be used for holding collections of dried

insects. Cork or ribbed packing paper may be fixed in the bottom for

supporting the insect pins. Moth balls or tobacco may be placed in

each box to keep out the insect pests which infest collections.

It is pleasant and profitable to take to the fields a small book

like this one, or even Comstock’s “Manual of Insects,” or Kellogg’s

“American Insects,” and study the insects and their habits where they

are found.

Captured insects which, in either the larval or perfect stage, are

injurious to vegetation, should always be killed after studying their

actions and external features, even if the internal structure is not

to be studied. Beneficial insects, such as ladybugs, ichneumon flies,

bees, mantis (devil’s horse), dragon flies, etc., should be set free

uninjured.

ANATOMY AND GENERAL CHARACTERISTICS OF THE CLASS INSECTA

The =body= of an insect (_e.g._ a wasp, Fig. 122) is divided by means

of two marked narrowings into three parts: the head (_K_), chest (_B_),

and abdomen (_H_).

[Illustration: FIG. 122.--A WASP.]

The =head= is a freely movable capsule bearing four pairs of

appendages. Hence it is regarded as having been formed by the union of

four rings, since the _ancestor of the insects_ is believed to have

consisted of similar rings, each ring bearing a pair of unspecialized

legs. The early grub or caterpillar stage of insects is believed to

resemble somewhat the ancestral form.

The typical =mouth parts= of an insect (Fig. 123), named in order from

above, are (1) an upper lip (labrum, _ol_) (2) a pair of biting jaws

(mandibles, _ok_) (3) a pair of grasping jaws (maxillæ, _A_, _B_), and

(4) a lower lip (labium, _m_, _a_, _b_). The grasping jaws bear two

pairs of jointed jaw fingers (maxillary palpi, _D_, _C_), and the lower

lip bears a pair of similar lip fingers (labial palpi, _d_). The biting

jaws move sideways; they usually have several pointed notches which

serve as teeth. Why should the grasping jaws be beneath the chewing

jaws? Why is it better for the lower lip to have fingers than the upper

lip? Why are the fingers (or palpi) jointed? (Watch a grasshopper or

beetle eating.) Why does an insect need grasping jaws?

[Illustration: FIG. 123.--MOUTH PARTS OF BEETLE.]

[Illustration: FIG. 124.--EXTERNAL PARTS OF A BEETLE.]

The chest, or =thorax=, consists of three rings (Fig. 124) called the

front thorax (prothorax), middle thorax (mesothorax) and hind thorax

(metathorax), or first, second, and third rings. The first ring bears

the first pair of legs, the second ring bears the second pair of legs

and the upper or front wings, and the third ring bears the third pair

of legs and the under or hind wings.

[Illustration: FIG. 125.--LEG OF INSECT.]

The =six feet= of insects are characteristic of them, since no other

animals have that number, the spider having eight, the crawfish and

crabs having ten, the centipedes still more, while the birds and

beasts have less than six. Hence the insects are sometimes called the

Six-Footed class (_Hexapoda_). The insects are the only animals that

have the =body in three divisions=. Man, beasts, and birds have only

two divisions (head and trunk); worms are not divided.

=Define= the class _insecta_ by the two facts characteristic of them

(_i.e._ possessed by them alone), viz.: Insects are animals with ____

and ____. Why would it be ambiguous to include “hard outer skeleton” in

this definition? To include “bilateral symmetry”? “Segmented body”? The

definition of a class must _include_ all the individuals of the class,

and _exclude_ all the animals that do not belong to the class.

The leg of an insect (Fig. 125) has five joints (two short joints,

two long, and the foot). Named in order from above, they are (1) the

hip (coxa), (2) thigh ring (trochanter), (3) thigh (femur), (4) the

shin (tibia), (5) the foot, which has five parts. Which of the five

joints of a wasp’s leg (Fig. 122) is thickest? Slenderest? Shortest?

One joint (which?) of the foot (Fig. 122) is about as long as the

other four joints of the foot combined. Is the relative length of

the joints of the leg the same in grasshoppers, beetles, etc., as

in the wasp (Figs.)? Figure 125 is a diagram of an insect’s leg cut

lengthwise. The leg consists of thick-walled tubes (_o_, _n_) with

their ends held together by thin, easy-wrinkling membranes which

serve as joints. Thus motion is provided for at the expense of

strength. When handling live insects they should never be held by

the legs, as the legs come off very easily. Does the joint motion of

insects most resemble the motion of hinge joints or ball-and-socket

joints? Answer by tests of living insects. There are no muscles in

the foot of an insect. The claw is moved by a muscle (_m_) in the

thigh with which it is connected by the long tendon (_z_, _s_, _t_,

_v_). In which part are the breathing muscles? As the wings are

developed from folds of the dorsal skin, the wing has two layers, an

upper and a lower layer. These inclose the so-called “nerves” or ribs

of the wing, each of which consists of a blood tube inclosed in an

air tube.

[Illustration: FIG. 126.--FOOT OF FLY, with climbing pads.]

The =abdomen= in various species consists of from five to eleven

overlapping rings with their foldlike joints between them. Does each

ring overlap the ring in front or the one behind it?

The =food tube= (Fig. 127) begins at the mouth, which usually contains

salivary glands (4, Fig. 127). What is the color of the grasshopper’s

saliva? The food tube expands first into a _croplike_ enlargement; next

to this is the _stomach_ (6, Fig. 127), which resembles the gizzard in

birds, as its inner wall is furnished with chitinous teeth (_b_, Fig.

114). These reduce the food fragments that were imperfectly broken up

by the biting jaws before swallowing. _Glands_ comparable to the liver

of higher animals open into the food tube where the stomach joins the

small intestine. At the junction of the small and large intestine (9)

are a number of _fine tubes_ (8) which correspond to kidneys and empty

their secretion into the large intestine.

[Illustration: FIG. 127.--VISCERA OF GRASSHOPPER. Key in text. Compare

with Fig. 114.]

[Illustration: FIG. 128.--AIR TUBES OF INSECT.]

The =breathing organs= of the insects are peculiar to them (see Fig.

128). They consist of tubes which are kept open by having in their

walls continuous spirals of horny material called _chitin_. Most

noticeable are the two large membranous tubes filled with air and

situated on each side of the body. Do these tubes extend through the

thorax? (Fig. 128.) The air reaches these two main tubes by a number

of pairs of short windpipes, or _tracheas_, which begin at openings

(_spiracles_). In which division are the spiracles most numerous? (Fig.

128.) Which division is without spiracles? Could an insect be drowned,

_i.e._ smothered, by holding its body under water? Could it be drowned

by immersing all of it but its head? The motion of the air through the

breathing tubes is caused by a bellowslike _motion of the abdomen_.

This is readily observed in grasshoppers, beetles, and wasps. As each

ring slips into the ring in front of it, the abdomen is shortened, and

the impure air, laden with carbon dioxid, is forced out. As the rings

slip out, the abdomen is extended and the fresh air comes in, bringing

oxygen.

[Illustration: FIG. 129.--INSECT’S HEART (plan).]

[Illustration: FIG. 130.--DIAGRAMS OF EVOLUTION OF PERICARDIAL SAC

around insect’s heart from a number of veins (Lankester).]

[Illustration: FIG. 131.--POSITION OF INSECT’S HEART, food tube, and

nerve chain.]

=The Circulation.=--Near the dorsal surface of the abdomen (Fig. 131)

extends the long, slender _heart_ (Fig. 129). The heart has divisions

separated by valvelike partitions. The blood comes into each of the

heart compartments through a pair of openings. The heart contracts

from the rear toward the front, driving the blood forward. The blood

contains bodies corresponding to the _white corpuscles_ of human blood,

but lacks the red corpuscles and the red color. The blood is sent even

to the wings. The _ribs_ on the wings consist of blood tubes inclosed

in air tubes, so that the blood vessels are surrounded by air, and the

purification of the blood is taking place throughout the course of

the circulation. Hence the imperfect circulation is no disadvantage.

The perfect provision for supplying oxygen explains the remarkable

activity of which insects are capable and their great strength, which,

considering their size, is unequaled by any other animals.

[Illustration: FIG. 132.--NERVOUS SYSTEM OF BEE.]

=The Nervous System.=--The heart in backboned animals, e.g. man, is

ventral and the chief nerve trunk is dorsal. As already stated, the

heart of an insect is dorsal; its chief nerve chain, consisting of

a _double row of ganglia_, is near the ventral surface (Fig. 131).

All the ganglia are below the food tube except the first pair in the

head, which are above the gullet. This pair may be said to correspond

somewhat to the brain of backboned animals; the nerves from the eyes

and feelers lead to it. With social insects, as bees and ants, it is

large and complex (Fig. 132). In a typical insect they are the largest

ganglia.

[Illustration: FIG. 133.--FEELER of a beetle.]

=The Senses.=--The sense of _smell_ of most insects is believed to be

located in the feelers. The organ of _hearing_ is variously located

in different insects. Where is it in the grasshopper? The organs of

_sight_ are highly developed, and consist of two compound eyes on the

side of the head and three simple eyes on the top or front of the head

between the compound eyes. The simple eye has nerve cells, pigments,

and a lens resembling the lens in the eyes of vertebrates (Fig. 134).

The compound eye (Fig. 135) has thousands of facets, usually hexagonal,

on its surface, the facets being the outer ends of cones which have

their inner ends directed toward the center of the eye. It is probable

that the large, or compound, eyes of insects only serve to distinguish

bright objects from dark objects. The simple eyes afford distinct

images of objects within a few inches of the eye. In general, the sight

of insects, contrary to what its complex sight organs would lead us

to expect, is not at all keen. Yet an insect can fly through a forest

without striking a twig or branch. Is it better for the eyes that are

immovable in the head to be large or small? Which has comparatively

larger eyes, an insect or a beast?

[Illustration: FIG. 134.--Diagram of simple eye of insect.

_L_, lens; _N_, optic nerve.]

[Illustration: FIG. 135.--COMPOUND EYE OF INSECT.

1, hexagonal facets of crystalline cones. 6, blood vessel in optic

nerve.]

=Inherited Habit, or Instinct.=--Insects and other animals inherit from

their parents their particular form of body and of organs which perform

the different functions. For example, they inherit a nervous system

with a structure similar to that of their parents, and hence with a

tendency to repeat similar impulses and acts. Repeated acts constitute

a habit, and _an inherited habit is called an instinct_. Moths, for

example, are used to finding nectar in the night-blooming flowers, most

of which are white. The habit of going to white flowers is transmitted

in the structure of the nervous system; so we say that moths have

an instinct to go to white objects; it is sometimes more obscurely

expressed by saying they are attracted or drawn thereby.

=Instincts are not Infallible.=--They are trustworthy in only one

narrow set of conditions. Now that man makes many fires and lights at

night, the instinct just mentioned often causes the death of the moth.

The instinct to provide for offspring is necessary to the perpetuation

of all but the simplest animals. The dirt dauber, or mud wasp, because

of inherited habit, or instinct, makes the cell of the right size, lays

the egg, and provides food for offspring that the mother will never

see. It seals stung and semiparalyzed spiders in the cell with the

egg. If you try the experiment of removing the food before the cell is

closed, the insect will bring more spiders; if they are removed again,

a third supply will be brought; but if taken out the third time, the

mud wasp will usually close the cell without food, and when the egg

hatches the grub will starve.

=The Development of Insects.=--The growth and molting of the

grasshopper from egg to adult has been studied. All insects do not

develop exactly by this plan. Some hatch from the egg in a condition

markedly different from the adult. The butterfly’s egg produces a

wormlike caterpillar which has no resemblance to the butterfly. After

it grows it forms an inclosing case in which it spends a quiet period

of development and comes out a butterfly. This change from caterpillar

to butterfly is called the _metamorphosis_. The life of an insect is

divided into four stages: (1) _egg_, (2) _larva_, (3) _pupa_, and (4)

_imago_, or perfect insect (Figs. 136, 137, 138).

[Illustration: FIG. 136.--Measuring worm, the larva of a moth.]

[Illustration: FIG. 137.--Pupa of a mosquito.]

[Illustration: FIG. 138.--THE FOUR STAGES OF A BOTFLY, all enlarged.

_a_, egg on hair of horse (bitten off and swallowed); _b_, larva; _c_,

larva with hooks for holding to lining of stomach; _d_, pupal stage,

passed in the earth; _e_, adult horse fly.]

The egg stage is one of development, no nourishment being absorbed.

The larval stage is one of voracious feeding and rapid growth. In the

pupa stage no food is taken and there is no growth in size, but rapid

development takes place. In the perfect stage food is eaten, but no

growth in size takes place. In this stage the eggs are produced. When

there is very little resemblance between the larva and imago, and

the pupa is quiescent, the metamorphosis, or change, is said to be

_complete_. When, as with the grasshopper, no very marked change takes

place between the larva and imago (that is to say, during the pupa

stage, which is active), the metamorphosis is said to be incomplete.

By studying the illustrations and specimens, and by thinking of your

past observations of insects, determine which of the insects in the

following list have a complete metamorphosis: beetle, house fly,

grasshopper, butterfly, cricket, wasp.

TABLE FOR CLASSIFYING INSECTS (_class Insecta_) INTO ORDERS

ORDER

A₁ =Biting Insects=; mouth parts for grasping and

biting

B₁ Wingless; changes (metamorphosis) NO WINGS

incomplete (_Aptera_)

B₂ Under wings thinner than upper wings, and FAN WINGS

fold like a fan beneath them; changes (_Orthoptera_)

incomplete

B₃ Upper wings hard and thick, protecting SHEATH WINGS

under wings, which fold both lengthwise and (_Coleoptera_)

crosswise beneath them; changes incomplete

B₄ All four wings nearly alike, finely veined,

transparent

C₁ Hind wings smaller than fore, two or NERVE WINGS

three filaments attached to abdomen, (_Neuroptera_)

antennæ long; changes complete

C₂ Hind wings not smaller than fore; no FALSE NERVE WINGS

filaments on abdomen, antennæ (_Pseudoneuroptera_)

inconspicuous; changes incomplete

A₂ =Sucking Insects=; mouth parts for sucking or

licking

B₁ Basal half of upper wing usually leathery, HALF WINGS

other half of wing transparent; lower lips (_Hemiptera_)

transformed into a tube; true bugs

B₂ Four wings covered by scales, holding-jaws SCALY WINGS

(maxillæ) elongated to form a sucking tube (_Lepidoptera_)

coiled under head; changes complete

B₃ Four wings, membranous, hind wings hook to JOINED WINGS

fore wings in flight; mouth parts for both (_Hymenoptera_)

biting and sucking; abdomen with sting;

changes complete

B₄ Two wings, mandibles rudimentary, mouth a TWO WINGS

soft beak (_Diptera_)

B₅ No wings, mandibles rudimentary, mouth a LOST WINGS

horny beak (_Siphonoptera_)

[Illustration: FIG. 139.--MAY FLY. What order (see table)?]

[Illustration: FIG. 140.--SILVER SCALE. (Order?)]

=Exercise in the Use of the Table or Key.=--Write the name of the

order after each of the following names of insects:--

Wasp (Fig. 122)

Weevil (Fig. 163)

Squash bug (Fig. 184)

Ant lion (Fig. 170)

Dragon fly (Fig. 177)

Ichneumon fly (Fig. 159)

House fly (Fig. 172)

Flea (Fig. 173)

Silver scale or earwig (Fig. 140)

Codling moth (Fig. 141)

Botfly (Fig. 138)

=Moths and Butterflies.=--Order ____? Why ____ (p. 82)?

The presence of scales on the wings is a never-failing test of a moth

or butterfly. The wings do not fold at all. They are so large and the

legs so weak and delicate that the butterfly keeps its balance with

difficulty when walking.

The maxillæ are developed to form the long sucking proboscis. How

do they fit together to form a tube? (See Fig. 147.) The proboscis

varies from a fraction of an inch in the “miller” to five inches in

some tropical moths, which use it to extract nectar from long tubular

flowers. When not in use, it is held coiled like a watch spring under

the head (Fig. 148). The upper lip (labrum), under lip (labium), and

lip fingers (labial palpi) are very small, and the mandibles small or

wanting (Fig. 146).

The metamorphosis is complete, the contrast between the caterpillar

or larva of the moth and butterfly and the adult form being very

great. The caterpillar has the three pairs of jointed legs typical

of insects; these are found near the head (Fig. 141). It has also

from three to five pairs of fleshy unjointed proplegs, one pair of

which is always on the last segment. How many pairs of proplegs has

the silkworm caterpillar? (Fig. 143.) The measuring worm, or looper?

(Fig. 136.) The pupa has a thin shell. Can you see external signs of

the antennæ, wings, and legs in this stage? (Fig. 143.) The pupa is

concealed by protective coloration, and is sometimes inclosed in a

silken cocoon which was spun by the caterpillar before the last molt.

Hairy caterpillars usually produce butterflies, and the naked ones

usually produce moths. Hairy ones are uncomfortable for birds to eat.

The naked and brightly marked ones (warning coloration) often contain

an acrid and distasteful fluid. The injuries from lepidoptera are done

in the caterpillar stage. The codling moth (Fig. 141) destroys apples

to the value of $6,000,000 annually. The clothes moth (Fig. 171) is a

household pest. The tent caterpillar denudes trees of their leaves.

The only useful caterpillar is the silkworm (Fig. 143). In Italy and

Japan many of the country dwellings have silk rooms where thousands of

these caterpillars are fed and tended by women and children. Why is

the cabbage butterfly so called? Why can it not eat cabbage? Why does

sealing clothes in a paper bag prevent the ravages of the clothes moth?

=Flight of Lepidoptera.=--Which appears to use more exertion to keep

afloat, a bird or a butterfly? Explain why. Of all flying insects

which would more probably be found highest up mountains? How does the

butterfly suddenly change direction of flight? Does it usually fly in

a straight or zigzag course? Advantage of this? Why is zigzag flight

unnecessary to moths? Bright colors are protective, as lepidoptera are

in greatest danger when at rest on flowers. Are the brightest colors on

upper or under side of wings of butterfly? Why? (Think of the colors in

a flower.) Why is it better for moths to hold their wings flat out when

at rest? Where are moths during the day? How can you test whether the

color of the wings is given by the scales?

State =how moths and butterflies differ= in respect to: body, wings,

feelers, habits; abundance of scales.

=Insects and Flowers.=--We are indebted to insects for the bright

colors and sweet honey of flowers. Flowers need insects to carry their

pollen to other flowers, as cross-fertilization produces the best

seeds. The insects need the nectar of the flowers for food, and the

bright colors and sweet odors are the advertisements of the flowers

to attract insects. There were no flowers in the world before flying

insects were developed. Moths, butterflies, and bees carry most pollen

(see Plant Biology, Chap. VI).

=Comparative Study.=--Make a table like this, occupying entire page

of notebook, leaving no margins, and fill in accurately:--

==========+=========+=========+=========+=========+=========+=========

| | | FLY | DRAGON | BEETLE | BEE

| GRASS- | BUTTER- | pp. 92, | FLY, | pp. 90, | pp. 88,

| HOPPER | FLY | 93 | p. 93 | 91 | 89

----------+---------+---------+---------+---------+---------+---------

| | | | | |

| | | | | |

----------+---------+---------+---------+---------+---------+---------

| | | | | |

| | | | | |

----------+---------+---------+---------+---------+---------+---------

| | | | | |

| | | | | |

----------+---------+---------+---------+---------+---------+---------

| | | | | |

| | | | | |

----------+---------+---------+---------+---------+---------+---------

| | | | | |

or | | | | | |

| | | | | |

==========+=========+=========+=========+=========+=========+=========

[Illustration: FIG. 141.--CODLING MOTH, from egg to adult. (See

Farmers’ Bulletin, p. 95.)]

[Illustration: FIG. 142.--CABBAGE BUTTERFLY, male and female, larva and

pupa.]

[Illustration: FIG. 143.--LIFE HISTORY OF SILKWORM.]

[Illustration: FIG. 144.--SCALES FROM BUTTERFLIES’ WINGS, as seen under

microscope.]

TO THE TEACHER: _These illustrated studies require slower and more

careful study than the text. One, or at most two, studies will

suffice for a lesson. The questions can be answered by studying the

figures. Weak observers will often fail and they should not be told,

but should try again until they succeed._

[Illustration: FIG. 145.--SCALES ON MOTH’S WING.]

[Illustration: FIG. 146.--HEAD OF BUTTERFLY.]

[Illustration: FIG. 147.--SECTION OF PROBOSCIS of butterfly showing

lapping joint and dovetail joint.]

[Illustration: FIG. 148.--HEAD OF BUTTERFLY (side view).]

FIGS. 141-148. =Illustrated Study of Lepidoptera.=--Study the stages

in the development of _codling moth_, _silkworm moth_, and _cabbage

butterfly_.

Where does each lay its eggs? What does the larva of each feed

upon? Describe the pupa of each. Describe the adult forms. Find the

_spiracles_ and _prolegs_ on the silkworm. Compare _antennæ_ of moth

and butterfly. Which has larger body compared to size of wings?

Describe the _scales_ from a butterfly’s wings as seen under

microscope (144). How are the scales arranged on moth’s wing (145)?

By what part is scale attached to wing? Do the scales overlap?

Study butterfly’s head and _proboscis_ (Figs. 146-148). What shape is

compound eye? Are the antennæ jointed? Is the proboscis jointed? Why

not call it a tongue? (See text.)

Which mouth parts have almost disappeared? What is the shape of cut

ends of halves of proboscis? How are the halves joined to form a tube?

If you saw a butterfly on a flower, for what purpose would you think

it was there? What, if you saw it on a leaf? How many spots on fore

wing of female cabbage butterfly? (Fig. 124, above.)

Does the silkworm chrysalis fill its cocoon? Eggs may be obtained

from U. S. Dept. of Agriculture.

[Illustration: FIG. 149.]

[Illustration: FIG. 150.]

[Illustration: FIG. 151.]

[Illustration: FIG. 152.]

[Illustration: FIG. 153.]

[Illustration: FIG. 154.]

[Illustration: FIG. 155.]

[Illustration: FIG. 156.]

[Illustration: FIG. 157.]

[Illustration: FIG. 158.--Anatomy of bee.]

FIGS. 149-161. =Illustrated Study of Bees and their Kindred.=--Head

of worker (Fig. 149): _o_, upper lip; _ok_, chewing jaws; _uk_,

grasping jaws; _kt_, jaw finger; _lt_, lip finger; _z_, tongue.

How do heads of drone (150) and queen (151) differ as to mouth, size

of the two compound eyes, size and position of the three simple eyes?

Is the head of a worker more like head of drone or head of queen?

Judging by the head, which is the queen, drone, and worker in Figs.

154-156? Which of the three is largest? Smallest? Broadest?

Figure 152 shows hind leg of worker. What surrounds the hollow,

_us_, which serves as pollen basket? The point, _fh_, is a tool for

removing wax which is secreted (_c_, Fig. 157) between rings on

abdomen. In Fig. 158, find relative positions of heart, _v_, food

tube, and nerve chain. Is crop, _J_, in thorax or abdomen? In this

nectar is changed to honey, that it may not spoil. Compare nerve

chain in Fig. 132.

[Illustration: FIG. 159.--Ichneumon fly.]

[Illustration: FIG. 160.]

[Illustration: FIG. 161.--Wasp using pebble.

From Peckham’s “Solitary Wasps,” Houghton, Mifflin & Co.]

Compare the cells of _bumble bee_ (Fig. 153) with those of hive bee.

They differ not only in shape but in material, being made of web

instead of wax, and they usually contain larvæ instead of honey. Only

a few of the queens among bumble bees and wasps survive the winter.

How do ants and honey bees provide for the workers also to survive

the winter? Name all the social insects that you can think of. Do

they all belong to the same order?

The ichneumon fly shown enlarged in Fig. 159 lays its eggs under

a caterpillar’s skin. What becomes of the eggs? The true size of

the insect is shown by the cross lines at _a_. The eggs are almost

microscopic in size. The pupæ shown (true size) on caterpillar are

sometimes mistaken for eggs. The same mistake is made about the pupa

cases of ants. Ichneumon flies also use tree-borers as “hosts” for

their eggs and larva. Is this insect a friend of man?

The _digging wasp_ (Figs. 160 and 161) supplies its larva with

caterpillars and closes the hole, sometimes using a stone as pounding

tool. Among the few other uses of tools among lower animals are the

elephant’s use of a branch for a fly brush, and the ape’s use of a

walking stick. This wasp digs with fore feet like a dog and kicks the

dirt out of the way with its hind feet.

Are the wings of bees and wasps more closely or less closely veined

than the wings of dragon flies? (Fig. 177.) For an interesting

account of the order “Joined-wings” (bees and their kindred) see

Comstock’s “Ways of the Six-footed,” Ginn & Co.

=Illustrated Study of Beetles.=

[Illustration: FIG. 162.--Diving beetle (_Dysticus_), with larva, _a_.]

[Illustration: FIG. 163.--Weevil.]

[Illustration: FIG. 164.]

[Illustration: FIG. 165.]

[Illustration: FIG. 166.--Click beetle.]

[Illustration: FIG. 167.--MAY BEETLE.]

[Illustration: FIG. 168.]

[Illustration: FIG. 169.--Colorado beetle (potato bug).]

=Illustrated Study of Beetles= (Figs. 162-169).--Write the life

history of the _Colorado beetle_, or potato bug (Fig. 169), stating

where the eggs are laid and describing the form and activities of

each stage (the pupal stage, _b_, is passed in the ground).

Do the same for the MAY BEETLE (Figs. 167-168). (It is a larva--the

white grub--for three years; hogs root them up.) Beetles, like moths,

may be trapped with a lantern set above a tub of water.

Where does a _Scarab_ or sacred beetle of the Egyptians, also called

tumble bug (Fig. 164), lay its eggs (Fig. 165)? Why?

How does the _click beetle_, or jack snapper (Fig. 166), throw itself

into the air? For what purpose?

The large proboscis of the _weevil_ (Fig. 163) is used for piercing a

hole in which an egg is laid in grain of corn, boll of cotton, acorn,

chestnut, plum, etc.

How are the legs and body of the _diving beetle_ suited for swimming

(Fig. 162)? Describe its larva.

What is the shape of the lady bug (Fig. 97)? It feeds upon plant lice

(Fig. 185). Is any beetle of benefit to man?

[Illustration: FIG. 170.--Life history of ant lion.]

=Illustrated Study of Ant Lion, or Doodle Bug= (Fig. 170).--Find the

pitfall (what shape?); the larva (describe it); the pupa case (ball

covered with web and sand); the imago. Compare imago with dragon fly

(Fig. 177).

How does ant lion prevent ant from climbing out of pitfall (see Fig.

170)? What is on edge of nearest pitfall? Explain.

Ant lions may be kept in a box half filled with sand and fed on ants.

How is the pitfall dug? What part of ant is eaten? How is unused food

removed?

How long is it in the larval state? Pupal state? Keep net over box to

prevent adult from flying away when it emerges.

[Illustration: FIG. 171.]

[Illustration: FIG. 172.--Metamorphosis of house fly (enlarged).]

[Illustration: FIG. 173.--Metamorphosis of flea.]

[Illustration: FIG. 174.--Louse.]

[Illustration: FIG. 175.--Bed bug. × 5.]

[Illustration: FIG. 176.--Life history of mosquito.]

=Illustrated Study of Insect Pests= (Figs. 171-176).--Why does the

_clothes moth_ (171) lay its eggs upon woolen clothing? How does the

larva conceal itself? The larva can cut through paper and cotton, yet

sealing clothes in bags of paper or cotton protects them. Explain.

The _house fly_ eats liquid sweets. It lays its eggs in horse dung.

Describe its larval and pupal forms. Banishing horses from city would

have what beneficial effect?

Describe the _louse_ and its eggs, which are shown attached to a

hair, natural size and enlarged.

Describe the _bed bug_. Benzine poured in cracks kills bed bugs. Do

bed bugs bite or suck? Why are they wingless?

Describe the larva, _f_, pupa, _g_, and the adult _flea_, all shown

enlarged. Its mandibles, _b_, _b_, are used for piercing. To kill

fleas lather dog or cat completely and let lather remain on five

minutes before washing. Eggs are laid and first stages passed in the

ground.

How does the _mosquito_ lay its eggs in the water without drowning

(176)? Why are the eggs always laid in still water? Which part of the

larva (wiggletail) is held to the surface in breathing? What part of

the pupa (called tumbler, or bull head) is held to the surface in

breathing? Give differences in larva and pupa. Where does pupa change

to perfect insect? Describe mouth parts of male mosquito (at left)

and female (at right). Only female mosquitoes suck blood. Males suck

juice of plants. Malarial mosquito alights with hind end of body

raised at an angle. For figure see Human Biology, Chap. X. Why does

killing fish and frogs increase mosquitoes? 1 oz. of kerosene for 15

ft. of surface of water, renewed monthly, prevents mosquitoes.

What is the use to the squash bug (Fig. 184) of having so bad an odor?

[Illustration: FIG. 177.]

FIG. 177. =Illustrated Study of Dragon Fly.=--3 shows dragon fly

laying its eggs in water while poised on wing. Describe the larval

form (water tiger). The extensible tongs are the maxillæ enlarged.

The pupa (1) is active and lives in water. Where does transformation

to adult take place (5)? Why are eyes of adult large? its legs small?

Compare front and hind wings.

Do the eyes touch each other? Why is a long abdomen useful in flight?

Why would long feelers be useless? What is the time of greatest

danger in the development of the dragon fly? What other appropriate

name has this insect? Why should we never kill a dragon fly?

[Illustration: FIG. 178.--The tarantula.]

[Illustration: FIG. 179.--Trap-door spider.]

[Illustration: FIG. 180.]

[Illustration: FIG. 181.--Anatomy of spider.]

[Illustration: FIG. 182.--Laying egg.]

[Illustration: FIG. 183.--Foot of spider.]

=Illustrated Study of Spiders= (Figs. 178-183).--The tarantula, like

most spiders, has eight simple eyes (none compound). Find them (Fig.

178). How do spiders and insects differ in body? Number of legs?

Which have more joints to legs? Does trap-door spider hold the door

closed (Fig. 179)? How many pairs of spinnerets for spinning web has

a spider (_Spw_, 180)? Foot of spider has how many claws? How many

combs on claws for holding web? Spiders spin a cocoon for holding

eggs. From what part of abdomen are eggs laid (_E_, 182; 2, 181)?

Find spider’s air sacs, _lu_, Fig. 181; spinning organs, _sp_; fang,

_kf_; poison gland, _g_; palpi, _kt_; eyes, _au_; nerve ganglia,

_og_, _ug_; sucking tube, _sr_; stomach, _d_; intestine, _ma_; liver,

_le_; heart, _h_, (black); vent, _a_. Give two reasons why a spider

is not an insect. How does it place its feet at each step (Fig.

110)? Does the size of its nerve ganglia indicate great or little

intelligence? Why do you think first part of body corresponds to both

head and thorax of insects?

[Illustration: FIG. 184.--Squash bug, or stink bug.]

The following Farmer’s Bulletins are available for free distribution to

those interested, by the U. S. Department of Agriculture, Washington,

D.C.:--

Farmer’s Bulletin No. 47, Insects affecting the Cotton Plant; No.

59, Bee Keeping; No. 70, The Principal Insect Enemies of the Grape;

No. 80, The Peach Twig Borer; No. 99, Three Insect Enemies of

Shade Trees; No. 120, The Principal Insects affecting the Tobacco

Plant; No. 127, Important Insecticides; No. 132, The Principal

Insect Enemies of Growing Wheat; No. 145, Carbon Bisulphid as an

Insecticide; No. 146, Insecticides and Fungicides; No. 152, revised,

Mange in Cattle; No. 153, Orchard Enemies in the Pacific Northwest;

No. 155, How Insects affect Health in Rural Districts; No. 159, Scab

in Sheep; No. 165, Silkworm Culture; No. 171, The Control of the

Codling Moth; No. 172, Scale Insects and Mites on Citrus Trees; No.

196, Usefulness of the Toad; No. 209, Controlling the Boll Weevil

in Cotton Seed and at Ginneries; No. 211, The Use of Paris Green in

controlling the Cotton Boll Weevil; No. 212, The Cotton Bollworm; No.

216, The Control of the Boll Weevil; No. 223, Miscellaneous Cotton

Insects in Texas; No. 247, The Control of the Codling Moth and Apple

Scab.

[Illustration: FIG. 185.--Female plant louse, with and without wings

(enlarged).]

The following bulletins of the Bureau of Entomology may be obtained

from the same source at the prices affixed: Bulletin No. 25 (old

series), Destructive Locusts, 15c.; No. 1 (new series), The Honey

Bee, 15c.; No. 3, The San José Scale, 10c.; No. 4, The Principal

Household Insects of the U. S., 10c.; No. 11, The Gypsy Moth in

America, 5c.; No. 14, The Periodical Cicada, 15c.; No. 15, The

Chinch Bug, 10c.; No. 16, The Hessian Fly, 10c.; Nos. 19, 23, and

33, Insects Injurious to Vegetables, 10c. each; No. 25, Notes on

Mosquitoes of the U. S., 10c.; No. 42, Some Insects attacking the

Stems of Growing Wheat, Rye, Barley, and Oats, 5c.; No. 50, The

Cotton Bollworm, 25c.; No. 51, The Mexican Boll Weevil, 25c.

Bureau of Plant Industry--Bulletin No. 88, Weevil-resisting

Adaptations of the Cotton Plant, 10c. This gives an instructive

account of the struggle of a plant for existence against an insect

enemy.

[Illustration: FIG. 186.--Gall fly (enlarged) and oak gall with larva,

and one from which a developed insect has escaped.]

[Illustration: FIG. 187.--PLAN OF MOUTH PARTS OF THE INSECT ORDERS.

_A_, straight wings, nerve wings, false nerve wings; _B_, joined wings;

_C_, scaly wings; _D_, half wings; _E_, two wings.

_ol_, upper lip; _ok_, biting jaws; _uk_, holding jaws; _ul_, under

lip; _kt_, jaw fingers; _lt_, lip fingers.]

[Illustration]

[Illustration: Pearl divers.]

CHAPTER IX

MOLLUSKS

THE FRESH-WATER MUSSEL

SUGGESTIONS.--The mussel is usually easy to procure from streams and

lakes by raking or dredging. In cities the hard-shelled clam, or

quahog, is for sale at the markets, and the following descriptions

apply to the anodon, unio, or quahog, with slight changes in regard

to the siphons. Mussels can be kept alive for a long time in a tub

with sand in the bottom. Pairs of shells should be at hand for study.

=External Features.=--The shell is an elongated oval, broader and

blunter at one end (Fig. 188). Why does the animal close its shell?

Does it open the shell? Why? Does it thrust the foot forward and pull

up to it, or thrust the foot back and push? (Mussels and clams have no

bones.) Does it go with the blunt or the more tapering end of the shell

forward? (Fig. 188.) Can a mussel swim? Why, or why not?

Lay the shells, fitted together, in your hand with _the hinge side away

from you and the blunt end to the left_ (Fig. 188). Is the right or the

left shell uppermost? Which is the top, or dorsal, side? Which is the

front, or anterior, end? Is the straight edge at the top or the bottom?

Our word “valve” is derived from a word meaning shell, because the

Romans used shells for valves in pumps. Is the mussel a univalve or a

bivalve? Which kind is the oyster? The snail?

Does the mussel have _bilateral symmetry_? Can you find a _horny

covering_, or epidermis, over the limy shell of a fresh specimen? Why

is it necessary? Does water dissolve lime? Horn? Find a bare spot. Does

any of the shell appear to be missing there?

The bare projection on each shell is called the _umbo_. Is the umbo

near the ventral or the dorsal line? The posterior or anterior end? Is

the surface of the umbones worn? Do the umbones rub against the sand as

the mussel plows its way along? How are the shells held together? Where

is the _ligament_ attached? (Fig. 189.) Is it opposite the umbones or

more to the front or rear? (Fig. 189.) Is the ligament of the same

material as the shell? Is the ligament in a compressed condition when

the shell is open or when it is closed? (Fig. 189.) When is the muscle

relaxed?

[Illustration: FIG. 188.--ANODON, or fresh-water mussel.]

[Illustration: FIG. 189.--DIAGRAM OF SHELL open and closed, showing

muscle, _m_, and ligament, _b_.]

[Illustration: FIG. 190.--MUSSEL crawling in sand.]

Notice the _lines_ on the outside of the shell (Figs. 188 and 190).

What point do they surround? They are _lines of growth_. Was each line

once the margin of the shell? If the shell should increase in size,

what would the present margin become? (Fig. 191.) Does growth take

place on the margin only? Did the shell grow thicker as it grew larger?

Where is it thinnest?

=Draw= the outside of the shell from the side. Draw a dorsal view. By

the drawings write the names of the margins of the shell (p. 98) and of

other parts learned, using lines to indicate the location of the parts.

Study the surface of the shell inside and out. The inside is called

_mother-of-pearl_. Is it of lime? Is the deeper layer of the shell of

lime? (When weak hydrochloric acid or strong vinegar is dropped on limy

substances, a gas, carbon dioxid, bubbles up.) Compare the thickness

of the _epidermal layer_, the middle _chalky layer_, and the inner,

_pearly layer_.

[Illustration: FIG. 191.--DIAGRAM. Change of points of attachment of

muscles as mussel enlarges. (Morgan.)]

=Anatomy of the Mussel.=--What parts protrude at any time beyond the

edge of the shell? (Fig. 190.) The shell is secreted by two folds of

the outer layer of the soft body of the mussel. These large, flaplike

folds hang down on each side, and are called the _mantle_. The two

great flaps of the mantle hang down lower than the rest of the body

and line the shell which it secretes (Fig. 192). The epidermis of

the mantle secretes the shell just as the epidermis of the crawfish

secretes its crust. Can you find the pallial line, or the line to which

the mantle extended on each shell when the animal was alive? A free

portion of the mantle extended like a fringe below the pallial line.

[Illustration: FIG. 192.--CROSS SECTION OF MUSSEL. (Diagram, after

Parker.)]

The shells were held together by two large _adductor muscles_. The

anterior adductor (Fig. 193) is near the front end, above the foot.

The posterior adductor is toward the rear end, but not so near the end

as the anterior. Can you find both _muscle scars_ in the shells? Are

they nearer the ventral or dorsal surface? The points of attachment

traveled downward and farther apart as the animal grew (see Fig. 191).

Higher than the larger scars are small scars, or impressions, where the

protractor and retractor muscles that extend and draw in the foot were

attached.

[Illustration: FIG. 193.--ANATOMY OF MUSSEL. (Beddard.)]

The muscular _foot_ extends downward in the middle, halfway between

the shells (Fig. 193). On each side of the foot and behind it hang

down the two pairs of =gills=, the outer pair and the inner pair (Fig.

192). They may be compared to four V-shaped troughs with their sides

full of holes. The water enters the troughs through the holes and

overflows above. Is there a marked difference in the size of the two

pairs of gills? A kind of chamber for the gills is made by the joining

of the mantle flaps below, along the ventral line. The mantle edges

are separated at two places, leaving openings called _exhalent_ and

_inhalent siphons_.

Fresh water with its oxygen, propelled by _cilia_ at the opening and on

the gills, enters through the lower or inhalent siphon, passes between

the gills, and goes to an upper passage, leaving the gill chamber by

a slit which separates the gills from the foot. For this passage, see

arrow (Fig. 194). The movement of the water is opposite to the way the

arrow points. After going upward and backward, the water emerges by the

exhalent siphon. The gills originally consisted of a great number of

filaments. These are now united, but not completely so, and the gills

still have a perforated or lattice structure. Thus they present a large

surface for absorbing oxygen from the water.

[Illustration: FIG. 194.--MUSSEL.

_A_, left shell and mantle flap removed.

_B_, section through body.

=Question:= Guided by other figures, identify the parts to which lines

are drawn.]

The =mouth= is in front of the foot, between it and the anterior

adductor muscle (Fig. 194). On each side of the mouth are the _labial

palps_, which are lateral lips (Fig. 195). They have cilia which convey

the food to the mouth after the inhalent siphon has sent food beyond

the gill chamber and near to the mouth. Thus both food and oxygen enter

at the inhalent siphon. The foot is in the position of a lower lip, and

if regarded as a greatly extended lower lip, the animal may be said to

have what is to us the absurd habit of using its lower lip as a foot.

The foot is sometimes said to be hatchet-shaped (Fig. 195). Do you see

any resemblance? Does the foot penetrate deep or shallow into the sand?

(Fig. 190.) Why, or why not?

[Illustration: FIG. 195.--MUSSEL. From below. Level cut across both

shells.

_Se_, palp; _P_, foot; _O_, mouth; _G_, liver; _Gg_, _Vg_, _Pg_,

ganglia.]

[Illustration: FIG. 196.--HEART OF MUSSEL, with intestine passing

through it.]

[Illustration: FIG. 197.]

The =food tube= of the mussel is comparatively simple. Behind the

mouth it enlarges into a swelling called the _stomach_ (Fig. 193).

The bile ducts of the neighboring liver empty into the stomach. The

_intestine_ makes several turns in the substance of the upper part

of the foot, and then passing upward, it runs approximately straight

to the vent (or anus), which is in the wall of the exhalent siphon.

The intestine not only runs through the _pericardial cavity_ (celome)

surrounding the heart, but through the ventricle of the heart itself

(Fig. 196).

The =kidneys= consist of tubes which open into the pericardial

chamber above and into the gill chamber below (_Neph._, Fig. 193).

The tubes are surrounded by numerous blood vessels (Fig. 198) and

carry off the waste matter from the blood.

The =nervous system= consists of _three pairs of ganglia_ and nerves

(Fig. 197). The ganglia are distinguishable because of their orange

color. The pedal ganglia on the front of the foot are easily seen

also; the visceral ganglia on the posterior adductor muscle may be

seen without removing the mussel from the shell (Fig. 193). The

reproductive organs open into the rear portion of the gill cavity

(Fig. 193). The sperms, having been set free in the water, are drawn

into the ova by the same current that brings the food. The eggs are

hatched in the gills. After a while the young mussels go out through

the siphon.

=Summary.=--In the gills (Fig. 198) the blood gains what? Loses what?

From the digestive tube the blood absorbs nourishment. In the kidneys

the blood is partly purified by the loss of nitrogenous waste.

[Illustration: FIG. 198.--DIAGRAM OF MUSSEL CUT ACROSS, showing mantle,

_ma_; gills, _kie_; foot, _f_; heart, _h_; intestine, _ed_.]

The cilia of the fringes on the inhalent, or lower, siphon, vibrate

continually and drive water and food particles into the mouth cavity.

Food particles that are brought near the labial palps are conveyed by

them to the mouth. As the water passes along the perforated gills, its

oxygen is absorbed; the mantle also absorbs oxygen from the water as

it passes. The water, as stated before, goes next through a passage

between the foot and palp into the cavity above the gills and on out

through the exhalent siphon. By stirring the water, or placing a drop

of ink near the siphons of a mussel kept in a tub, the direction of its

flow may be seen. The pulsations of the heart are plainly visible in a

living mollusk.

=Habits of the Mussel.=--Is it abundant in clear or muddy water; swift,

still, or slightly moving water? Describe its track or furrow. What

is its rate of travel? Can you distinguish the spots where the foot

was attached to the ground? How long is one “step” compared to the

length of the shell? The animal usually has the valves opened that it

may breathe and eat. The hinge ligament acts like the case spring of a

watch, and holds the valves open unless the adductor muscles draw them

together (Fig. 189).

When the mussel first hatches from the egg, it has a triangular shell.

It soon attaches itself to some fish and thus travels about; after two

months it drops to the bottom again.

=Other Mollusca.=--The _oyster’s_ shells are not an exact pair, the

shell which lies upon the bottom being hollowed out to contain the

body, and the upper shell being flat. Can you tell by examining an

oyster shell which was the lower valve? Does it show signs of having

been attached to the bottom? The young oyster, like the young mussel,

is free-swimming. Like the arthropoda, most mollusks undergo a

metamorphosis to reach the adult stage (Fig. 199).

[Illustration: FIG. 199.--OYSTER.

_C_, mouth; _a_, vent; _g_, _g′_, ganglia; _mt_, mantle; _b_, gill.]

[Illustration: FIG. 200.--TROCHUS.]

[Illustration: FIG. 201.--CYPRÆA. (Univalve, with a long opening to

shell.)]

Examine the shells of clams, snails, scallops, and cockles. Make

drawings of their shells. The slug is very similar to the snail except

that it has no shell. If the shell of the snail shown in Fig. 202 were

removed, there would be left a very good representation of a slug.

=Economic Importance of Mollusca.=--Several species of clams are eaten.

One of them is the _hard-shell clam_ (quahog) found on the Atlantic

coast from Cape Cod to Texas. Its shell is white. It often burrows

slightly beneath the surface. The _soft-shell clam_ is better liked

as food. It lives along the shores of all northern seas. It burrows a

foot beneath the surface and extends its siphons through the burrow to

the surface when the tide is in, and draws into its shell the water

containing animalcules and oxygen.

_Oysters_ to the value of many millions of dollars are gathered and

sold every year. The most valuable oyster fisheries of the United

States are in Chesapeake Bay. The young oysters, or “spat,” after they

attach themselves to the bottom in shallow water, are transplanted.

New oyster beds are formed in this way. The beds are sometimes strewn

with pieces of rock, broken pottery, etc., to encourage the oysters

to attach themselves. The dark spot in the fleshy body of the oyster

is the digestive gland, or liver. The cut ends of the tough adductor

muscles are noticeable in raw oysters. The starfish is very destructive

in oyster beds.

_Pearls_ are deposited by bivalves around some irritating particle

that gets between the shell and the mantle. The pearl oyster furnishes

most of the pearls; sometimes pearls of great value are obtained from

fresh-water mussels in the United States. Name articles that are made

partly or wholly of mother-of-pearl.

[Illustration: FIG. 202.--A SNAIL.

_l_, mouth; _vf_, _hf_, feelers; _e_, opening of egg duct; _fu_, foot;

_ma_, mantle; _lu_, opening to lung; _a_, vent.]

=Study of a Live Snail or Slug.=--Is its body dry or moist? Do

land snails and slugs have lungs or gills? Why? How many pairs of

tentacles has it? What is their relative length and position? The

eyes are dark spots at bases of tentacles of snail and at the tips

of the rear tentacles of slug. Touch the tentacles. What happens? Do

the tentacles simply stretch, or do they turn inside out as they are

extended? Is the respiratory opening on the right or left side of the

body? On the mantle fold or on the body? (Figs. 202-3-4.) How often

does the aperture open and close?

[Illustration: FIG. 203.--A SLUG.]

[Illustration: FIG. 204.--CIRCULATION AND RESPIRATION IN SNAIL.

_a_, mouth; _b_, _b_, foot; _c_, vent; _d_, _d_, lung; _h_, heart.

Blood vessels are black. (Perrier.)]

Place the snail in a moist tumbler. Does the whole under surface seem

to be used in creeping? Does the creeping surface change shape as the

snail creeps? Do any folds or wrinkles seem to move either toward

the front or rear of its body? Is enough mucus left to mark the path

traveled? The fold moves to the front, adheres, and smooths out as

the slug or snail is pulled forward.

=Cephalopods.=--The highest and best developed mollusks are the

=cephalopods=, or “head-footed” mollusks. Surrounding the mouth

are eight or ten appendages which serve both as feet and as arms.

These appendages have two rows of sucking disks by which the animal

attaches itself to the sea bottom, or seizes fish or other prey with

a firm grip. The commonest examples are the _squid_, with a long body

and ten arms, and the _octopus_, or devilfish, with a short body and

eight arms. Cephalopods have strong biting mouth parts and complex

eyes somewhat resembling the eyes of backboned, or vertebrate,

animals. The large and staring eyes add to the uncanny, terrifying

appearance.

[Illustration: FIG. 205.--A SQUID.]

The sepia or “ink” discharged through the siphon of the squid makes

a dark cloud in the water and favors its escape from enemies almost

as much as its swiftness (Fig. 205). The squid sometimes approaches

a fish with motion so slow as to be imperceptible, and then suddenly

seizes it, and quickly kills it by biting it on the back behind the

head.

The octopus is more sluggish than the squid. Large species called

devilfish sometimes have a spread of arms of twenty-five feet. The

_pearly nautilus_ (Fig. 206) and the _female of the paper argonaut_

(Fig. 207) are examples of cephalopods that have shells. The

_cuttlefish_ is closely related to the squid.

[Illustration: FIG. 206.--PEARLY NAUTILUS. (Shell sawed through to show

chambers used when it was smaller, and siphuncle, _S_, connecting them.

Tentacles, _T_.)]

[Illustration: FIG. 207.--PAPER ARGONAUT (female).

× ¹⁄₃ (_i.e._ the animal is three times as long and broad as figure).]

[Illustration: FIG. 208.--PAPER ARGONAUT (male). × ¹⁄₂.]

=General Questions.=--The living parts of the mussel are very soft, the

name mollusca having been derived from the Latin word _mollis_, soft.

Why is it that the softest animals, the mollusks, have the hardest

coverings?

To which class of mollusks is the name acephala (headless) appropriate?

Lamellibranchiata (platelike gills)?

Why is a smooth shell suited to a clam and a rough shell suited to an

oyster? Why are the turns of a snail’s shell so small near the center?

Why does the mussel have no use for head, eyes, or projecting feelers?

In what position of the valves of a mussel is the hinge ligament in a

stretched condition? How does the shape of the mussel’s gills insure

that the water current and blood current are brought in close contact?

The three classes of mollusks are: the pelecypoda (hatchet-footed);

gastropoda (stomach-footed); and cephalopoda (head-footed). Give an

example of each class.

Comparison of Mollusks.

=====+==========+==========+==========

| MUSSEL | SNAIL | SQUID

-----+----------+----------+----------

| | |

Shell| | |

| | |

-----+----------+----------+----------

| | |

Head | | |

| | |

-----+----------+----------+----------

| | |

Body | | |

| | |

-----+----------+----------+----------

| | |

Foot | | |

| | |

-----+----------+----------+----------

| | |

Gills| | |

| | |

-----+----------+----------+----------

| | |

Eyes | | |

| | |

=====+==========+==========+==========

=Comparative Review.=--(To occupy an entire page in notebook.)

============+==========+==========+==========+==========+==========

------------+----------+----------+----------+----------+----------

| | | | |

------------+----------+----------+----------+----------+---------

for | | | | |

------------+----------+----------+----------+----------+---------

------------+----------+----------+----------+----------+---------

------------+----------+----------+----------+----------+---------

| | | | |

| | | | |

============+==========+==========+==========+==========+=========

CHAPTER X

FISHES

[Illustration]

SUGGESTIONS.--The behavior of a live fish in clear water, preferably

in a glass vessel or an aquarium, should be studied. A skeleton may

be prepared by placing a fish in the reach of ants. Skeletons of

animals placed on ant beds are cleaned very thoroughly. The study of

the perch, that follows, will apply to almost any common fish.

=Movements and External Features.=--What is the _general shape of the

body_ of a fish? How does the dorsal, or upper, region differ in form

from the ventral? Is there a narrow part or neck where the head joins

the trunk? Where is the body thickest? What is the ratio between the

length and height? (Fig. 209.) Are the right and left sides alike? Is

the symmetry of the fish bilateral or radial?

The _body of the fish may be divided_ into three regions,--the head,

trunk, and tail. The trunk begins with the foremost scales; the tail is

said to begin at the vent, or anus. Which regions bear appendages? Is

the head movable independently of the trunk, or do they move together?

State the advantage or disadvantage in this. Is the body depressed

(flattened vertically) or compressed (flattened laterally)? Do both

forms occur among fishes? (See figures on pages 123, 124.)

How is the _shape of the body advantageous for movement_? Can a fish

turn more readily from side to side, or up and down? Why? Is the

head wedge-shaped or conical? Are the jaws flattened laterally or

vertically? The fish swims in the water, the bird swims in the air.

Account for the differences in the shape of their bodies.

[Illustration: FIG. 209.--WHITE PERCH (_Morone Americana_).]

Is the _covering of the body_ like the covering of any animal yet

studied? The scales are attached in little pockets, or folds, in the

skin. Observe the shape and size of scales on different parts of the

body. What parts of the fish are without scales? Examine a single

scale; what is its shape? Do you see concentric lines of growth on a

scale? Sketch a few of the scales to show their arrangement. What is

the use of scales? Why are no scales needed on the head? How much of

each scale is hidden? Is there a film over the scale? Are the colors in

the scale or on it?

=The Fins.=--Are the movements of the fish active or sluggish? Can it

remain stationary without using its fins?

Can it move backward? How are the fins set in motion? What is the color

of the flesh, or muscles, of a fish? Count the fins. How many are in

pairs? (Fig. 209.) How many are vertical? How many are on the side?

How many are on the middle line? Are the paired or unpaired fins more

effective in balancing the fish? In turning it from side to side? In

raising and lowering the fish? In propelling it forward? How are some

of the fins useful to the fish besides for balancing and swimming?

The hard _spines_ supporting the fins are called the fin rays. The fin

on the dorsal line of the fish is called the _dorsal_ fin. Are its

rays larger or smaller than the rays of the other fins? The perch is

sometimes said to have two dorsal fins, since it is divided into two

parts. The fin forming the tail is called the tail fin, or _caudal_

fin. Are its upper and lower corners alike in all fishes? (Fig. 228.)

On the ventral side, just behind the vent, is the ventral fin, also

called the anal fin. The three fins mentioned are unpaired fins. Of the

four-paired fins, the pair higher on the sides (and usually nearer the

front) are the _pectoral_ fins. The pair nearer the ventral line are

the _pelvic_ fins. They are close together, and in many fish are joined

across the ventral line. The ventral fins are compared to the legs,

and the pectoral fins to the arms, of higher vertebrates. (Fig. 244.)

Compare fins of fish, pages 123, 124.

Make a =drawing= of the fish seen from the side, omitting the scales

unless your drawing is very large.

Are the =eyes= on the top or sides of the head, or both? Can a fish

shut its eyes? Why, or why not? Is the eyeball bare, or covered by

a membrane? Is the covering of the eyeball continuous with the skin

of the head? Is there a fold or wrinkle in this membrane or the

surrounding skin? Has the eye a pupil? An iris? Is the eye of the

fish immovable, slightly movable, or freely movable? Can it look with

both eyes at the same object? Is the _range of vision_ more upward or

downward? To the front or side? In what direction is vision impossible?

Can a fish close its eyes in sleep? Does the eyeball appear spherical

or flattened in front? The ball is really spherical, the lens is very

convex, and fish are nearsighted. Far sight would be useless in a dense

medium like water.

[Illustration: FIG. 210.--BLACKBOARD OUTLINE OF FISH.]

In what direction are the =nostrils= from the eyes? (Fig. 211.) There

are two pairs of nostrils, but only one pair of nasal cavities, with

two nostrils opening into each. There are no nasal passages to the

mouth, as the test with a probe shows that the cavities do not open

into the mouth. What two functions has the nose in man? What function

has it in the fish?

[Illustration: FIG. 211.--HEAD OF CARP.]

There are _no external_ =ears=. The ear sacs are embedded in the bones

of the skull. Is hearing acute or dull? When fishing, is it more

necessary not to talk or to step lightly, so as not to jar the boat or

bank?

What is the use of the large openings found at the back of the head on

each side? (Fig. 211.) Under the skin at the sides of the head are thin

membrane bones formed from the skin; they aid the skin in protection.

Just under these membrane bones are the gill covers, of true bone.

Which consists of more parts, the membranous layer, or the true bony

layer in the gill cover? (Figs. 211 and 212.)

[Illustration: FIG. 212.--SKELETON OF PERCH.]

Is the =mouth= large or small? Are the _teeth_ blunt or pointed? Near

the outer edge, or far in the mouth? (Fig. 212.) Does the fish have

lips? Are the teeth in one continuous row in either jaw? In the upper

jaw there are also teeth on the premaxillary bones. These bones are in

front of the maxillary bones, which are without teeth. Teeth are also

found in the roof of the mouth, and the tongue bears horny appendages

similar to teeth. Are the teeth of the fish better suited for chewing

or for grasping? Why are teeth on the tongue useful? Watch a fish

eating: does it chew its food? Can a fish taste? Test by placing bits

of brown paper and food in a vessel or jar containing a live fish. Is

the throat, or gullet, of the fish large or small?

The =skeleton= of a fish is simpler than the skeleton of other

backboned animals. Study Fig. 212 or a prepared skeleton. At first

glance, the skeleton appears to have two vertebral columns. Why?

What bones does the fish have that correspond to bones in the human

skeleton? Are the projections (processes) from the vertebræ long or

short? The _ribs_ are attached to the vertebræ of the trunk, the last

rib being above the vent. The tail begins at the vent. Are there more

tail vertebræ or trunk vertebræ? Are there any neck (cervical) vertebræ

(_i.e._ in front of those that bear ribs)? The first few ribs (how

many?) are attached to the central body of the vertebræ. The remaining

ribs are loosely attached to processes on the vertebræ. The ribs of

bony fishes are not homologous with the ribs of the higher vertebrates.

In most fishes there are bones called intermuscular bones attached to

the first ribs (how many in the perch?) which are possibly homologous

to true ribs; that is, true ribs in the higher vertebrates may have

been developed from such beginnings.

[Illustration: FIG. 213.]

Which, if any, of the _fin skeletons_ (Fig. 214) are not attached

to the general skeleton? Which fin is composed chiefly of tapering,

pointed rays? Which fins consist of rays which subdivide and widen

toward the end? Which kind are stiff, and which are flexible? Which

of the fin rays are segmented, or in two portions? The outer segment

is called the radial, the inner the basal segment. Which segments are

longer? There is one basal segment that lacks a radial segment; find it

(Fig. 212).

[Illustration: FIG. 214.--SOFT-RAYED AND SPINY-RAYED FINS.]

What is the advantage of the backbone plan of structure over the

armor-plate plan? You have seen the spool-like body of the vertebra in

canned salmon. Is it concave, flat, or convex at the ends?

[Illustration: FIG. 215.--CARP, with right gill cover removed to show

gills.]

[Illustration: FIG. 216.--SKELETON AROUND THROAT OF FISH.]

The =gills= are at the sides of the head (Fig. 215) under the opercula,

or gill covers. What is the color of the gills? Do the blood vessels

appear to be very near the surface of the gills, or away from the

surface? What advantage in this? Are the gills smooth or wrinkled?

(Fig. 215.) What advantage? The bony supports of the gills, called the

gill arches, are shown in Fig. 216 (_k_₁ to _k_₄). How many arches

on each side? The gill arches have projections on their front sides,

called gill rakers, to prevent food from being washed through the

clefts between the arches. The fringes on the rear of the gill arches

are called the gill filaments (_a_, Fig. 216). These filaments support

the thin and much-wrinkled borders of the gills, for the gills are

constructed on the plan of exposing the greatest possible surface to

the water. Compare the plan of the gills and the human lungs. The gill

opening on each side is guarded by seven rays (_kh_, Fig. 216) along

the hinder border of the gill cover. These rays grow from the tongue

bone. (_Zu_, Fig. 216. This is a rear view.)

[Illustration: FIG. 217.--CIRCULATION IN GILLS.]

[Illustration: FIG. 218.--NOSTRILS, MOUTH, AND GILL OPENINGS OF

STING-RAY.]

Watch a live fish and determine how the water is forced between the

gills. Is the mouth opened and closed in the act of breathing? Are the

openings behind the gill covers opened and closed? How many times per

minute does fresh water reach the gills? Do the mouth and gill covers

open at the same time? Why must the water in contact with the gills

be changed constantly? Why does a fish usually rest with its head up

stream? How may a fish be kept alive for a time after it is removed

from the water? Why does drying of the gills prevent breathing? If the

mouth of a fish were propped open, and the fish returned to the water,

would it suffocate? Why, or why not?

[Illustration: FIG. 219.--GILL OPENINGS OF EEL.]

=Food Tube.=--The gullet is short and wide. The stomach is elongated

(Fig. 220). There is a slight constriction, or narrowing, where it

joins the intestine. Is the intestine straight, or does it lie in

few or in many loops? (Fig. 220.) The liver has a gall bladder and

empties into the intestine through a bile duct. Is the liver large or

small? Simple or lobed? The spleen (_mi_, Fig. 220) lies in a loop

of the intestine. The last part of the intestine is straight and

is called the rectum. Is it of the same size as the other portions

of the intestine? The fish does not possess a pancreas, the most

important digestive gland of higher vertebrates.

[Illustration: FIG. 220.--ANATOMY OF CARP. (See also colored figure 4.)

_bf_, barbels on head (for feeling); _h_, ventricle of heart; _as_,

aortic bulb for regulating flow to gills; _vk_, venous sinus; _ao_,

dorsal aorta; _ma_, stomach; _l_, liver; _gb_, gall cyst; _mi_, spleen;

_d_, small intestine; _md_, large intestine; _a_, vent; _s_, _s_, swim

bladder; _ni_, _ni_, kidney; _hl_, ureter; _hb_, bladder; _ro_, eggs

(roe); _mhe_, opening of ducts from kidney and ovary.

=Questions:= Are the kidneys dorsal or ventral? The swim bladder? Why?

Why is the swim bladder double? Does blood enter gills above or below?]

The _ovary_ lies between the intestine and the air bladder. In Fig.

220 it is shown enlarged and filled with egg masses called roe. It

opens by a pore behind the vent. The silver lining of the body cavity

is called the peritoneum. (See Chap. VII, Human Biology.)

Is the _air bladder_ simple or partly divided in the perch? In the

carp? (Fig. 220.) Is it above or below the center of the body? Why?

The air bladder makes the body of the fish about as light as water

that it may rise and sink with little effort. When a fish dies, the

gases of decomposition distend the bladder and the abdomen, and the

fish turns over. Why?

Where are the _kidneys_? (Fig. 220.) Their ends unite close under the

spinal column. The ureters, or tubes, leading from them, unite, and

after passing a small urinary bladder, lead to a tiny urinary pore

just behind the opening from the ovary. (Colored figure 4.)

=The Circulation.=--The fish, unlike other vertebrates, has its

breathing organs and its heart in its head. The gills have already

been described. The heart of an air-breathing vertebrate is near its

lungs. Why? The _heart_ of a fish is near its gills for the same

reason. The heart has one auricle and one ventricle. (Colored figure

1.)

[Illustration: FIG. 221.--PLAN OF CIRCULATION.

_Ab_, arteries to gills; _Ba_, aortic bulb; _V_, ventricle.]

Blood returning to the heart comes through several veins into a

_sinus_, or antechamber, whence it passes down through a valve into

the _auricle_; from the auricle it goes forward into the _ventricle_.

The ventricle sends it into an _artery_, not directly, but through

a _bulb_ (as, Fig. 220), which serves to maintain a steady flow,

without pulse beats, into the large artery (_aorta_) leading to the

gills. The arteries leading from the gills join to form a _dorsal

aorta_ (_Ao_, Fig. 221), which passes backward, inclosed by the lower

processes of the spinal column. After going through the _capillaries_

of the various organs, the blood returns to the heart through veins.

The _color of the blood_ is given by red corpuscles. These are

nucleated, oval, and larger than the blood corpuscles of other

vertebrates. The blood of the fish is slightly above the temperature

of the water it inhabits.

[Illustration: FIG. 222.--BRAIN OF PERCH, from above.

_n_, end of nerve of smell; _au_, eye; _v_, _z_, _m_, fore, mid, and

hind brain; _h_, spinal bulb; _r_, spinal cord.]

Notice the general shape of the =brain= (Fig. 222). Are its

subdivisions distinct or indistinct? Are the lobes in pairs? The

middle portion of the brain is the widest, and consists of the two

_optic lobes_. From these lobes the optic nerves pass beneath the

brain to the eyes (_Sn_, Fig. 223). In front of the optic lobes lie

the two cerebral lobes, or the _cerebrum_. The small _olfactory

lobes_ are seen (Fig. 224) in front of the cerebrum. The olfactory

nerves may be traced to the nostrils. Back of the optic lobes (mid

brain) is the cerebellum (hind brain), and back of it is the _medulla

oblongata_, or beginning of the spinal cord.

[Illustration: FIG. 223.--BRAIN OF PERCH, side view.]

[Illustration: FIG. 224.--BRAIN OF PERCH, from below.]

Taking the eyeball for comparison, is the whole brain as large as one

eyeball? (Fig. 222.) Judging from the size of the parts of the brain,

which is more important with the fish, thinking or perception? Which

is the most important sense?

The scales along a certain line on each side of the fish, called the

lateral line, are perforated over a series of lateral line sense

organs, supposed to be the chief organs of _touch_ (see Fig. 209).

[Illustration: FIG. 225.--THE STICKLEBACK. Instead of depositing the

eggs on the bottom, it makes a nest of water plants--the only fish that

does so--and bravely defends it.]

=Questions.=--Which of the fins of the fish have a use which

corresponds to the keel of a boat? The rudder? A paddle for sculling?

An oar? State several reasons why the head of the fish must be very

large, although the brain is very small. Does all the blood go to the

gills just after leaving the heart?

Make a list of the different species of fish found in the waters of

your neighborhood; in the markets of your town.

[Illustration: FIG. 226.--ARTIFICIAL FECUNDATION. The egg-cells and

sperm-cells are pressed out into a pan of water.]

[Illustration: FIG. 227.--NEWLY HATCHED TROUT, with yolk-sac adhering,

eyes large, and fins mere folds of the skin. (Enlarged.)]

=Reproduction.=--The female fish deposits the unfertilized eggs,

or ova, in a secluded spot on the bottom. Afterward the male fish

deposits the sperms in the same place (see Fig. 225). The eggs, thus

unprotected, and newly hatched fish as well, are used for food by

fish of the same and other species. To compensate for this great

destruction, most fish lay (spawn) many thousands of eggs, very few

of which reach maturity. Higher vertebrates (_e.g._ birds) have, by

their superior intelligence, risen above this wasteful method of

reproduction. Some kinds of marine fish, notably cod, herring, and

salmon, go many miles up fresh rivers to spawn. It is possible that

this is because they were originally fresh-water species; yet they die

if placed in fresh water except during the spawning season. They go

because of _instinct_, which is simply an inherited habit. Rivers may

be safer than the ocean for their young. They are worn and exhausted by

the journey, and never survive to lay eggs the second time.

[Illustration: FIG. 228.--A SHARK (_Acanthias vulgaris_).]

The _air bladder is developed from the food tube_ in the embryo fish,

and is homologous with lungs in the higher vertebrates. Are their

functions the same?

Fish that _feed on flesh have a short intestine_. Those that eat plants

have a long intestine. Which kind of food is more quickly digested?

There are _mucous glands in the skin_ of a fish which supply a

secretion to facilitate movement through the water; hence a freshly

caught fish, before the secretion has dried, feels very slippery.

The air bladder, although homologous to lungs, is not a breathing organ

in common fishes. It is filled by the formation of gases from the

blood, and can be made smaller by the contraction of muscles along the

sides of the body; this causes the fish to sink. In the gar and other

ganoids, the air bladder contains blood vessels, is connected with the

gullet, and is used in breathing. Organs _serving the same purpose_ in

different animals are said to be _analogous_. To what in man are the

gills of the fish analogous? Organs having _a like position and origin_

are said to be _homologous_. The air bladders of a fish are homologous

with the lungs of man; but since they have not the same use they are

not analogous.

How does the tail of a shark or a gar differ from the tail of common

fishes? (Fig. 228.) Do you know of fish destitute of scales? Do you

know of fish with whiplike feelers on the head? (Figs.) Why are most

fishes white on the under side?

=Comparative Review.=--(Copy table on one page or two facing pages of

notebook.)

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[Illustration: FIG. 229.--DRAWING THE SEINE.]

[Illustration: FIG. 230.--SUNFISH.

FIG. 231.--TUNNY.

FIG. 232.--SWORDFISH.

FIG. 233.--SWELLFISH.

FIG. 234.--TURBOT.

FIG. 235.--CARP.

FIG. 236.--HERRING.

FIG. 237.--SPECKLED TROUT.

FIG. 238.--PERCH.

FIG. 239.--SALMON.

=Seven Food Fish. Three Curious Fish.=

SPECIAL REPORTS. (Encyclopedia, texts, dictionary.)]

[Illustration: FIG. 240.--SEA HORSE (_hippocampus_), with incubating

pouch, _Brt._

FIG. 241.--BAND FISH.

FIG. 242.--TORPEDO. Electrical organs at right and left of brain.

FIG. 243.--LANTERN FISH (_Linophryne lucifer_). (After Collett.)

FIG. 244.--LUNG FISH of Australia (_Ceratodus miolepis_).

FIG. 245.--TRUNK FISH.

FIG. 246.--SEAWEED FISH. × ¹⁄₅ (_Phyllopteryx eques_).

=Remarkable Fish.= SPECIAL REPORTS. (Encyclopedia, texts, dictionary.)]

KEY TO THE BRANCHES, OR SUB-KINGDOMS

A₁ =One-celled Animals= (_Protozoans_) I. PROTOZOANS

A₂ =Many-celled Animals= (_Metazoans_)

B₁ RADIATE (around a center). Without head;

all aquatic, resembling plants, and often

fixed to bottom

C₁ Walls of body serving as digestive

organs

D₁ Many openings, no tentacles II. SPONGES

(_Porifera_)

D₂ One opening, which is both mouth and III. POLYPS

vent; tentacles for seizing prey (_Cœlenterata_)

C₂ Digestive tube distinct from body wall, IV. ECHINODERMS

spiny skin

B₂ BILATERAL. With anterior and posterior

end; dorsal and ventral surface

C₁ Body of successive segments; legs V. VERMES

without joints

C₂ External skeleton of successive rings; VI. ARTHROPODS

jointed legs

C₃ Body soft; no skeleton; usually bearing VII. MOLLUSKS

a limy shell

C₄ Internal jointed skeleton, attached to VIII. VERTEBRATES

an axis or vertebral column

=Examples.=--Tell the branch to which each of the following

animals belongs: crayfish, earthworm, thousand leg, white grub,

sea anemone, ameba, tapeworm, caterpillar, beetle, sparrow, snake,

oyster, starfish, fish. Be prepared to state the reason for each

classification.

The =classes= in the branch =vertebrata= are: 1. Fishes (_pisces_). 2.

Frogs and Salamanders (_batrachia_). 3. Reptiles (_reptilia_). 4. Birds

(_aves_). 5. Mammals (_mammalia_).

[Illustration: FIG. 247.--A SNAIL. (Which branch? Why?)]

CHAPTER XI

BATRACHIA

The theory of evolution teaches that animal life began in a very simple

form in the sea, and that afterward the higher sea animals lost their

gills and developed lungs and legs and came out to live upon the land;

truly a marvelous procedure, and incredible to many, although the

process is repeated every spring in countless instances in pond and

brook.

In popular language, every cold-blooded vertebrate breathing with

lungs is called a reptile. The name reptile is properly applied only

to lizards, snakes, turtles, and alligators. The common mistake of

speaking of frogs and salamanders as reptiles arises from considering

them only in their adult condition. Reptiles hatch from the egg as tiny

reptiles resembling the adult forms; frogs and salamanders, as every

one knows, leave the egg in the form of tadpoles (Fig. 248). The fact

that frogs and salamanders begin active life as fishes, breathing by

gills, serves to distinguish them from other cold-blooded animals, and

causes naturalists to place them in a separate class, called batrachia

(twice breather) or amphibia (double life).

TADPOLES

SUGGESTIONS.--Tadpoles may be studied by placing a number of frog’s

eggs in a jar of water, care being taken not to place a large number

of eggs in a small amount of water. When they hatch, water plants

(_e.g._ green algæ) should be added for food. The behavior of frogs

may be best studied in a tub of water. A toad in captivity should be

given a cool, moist place, and fed well. A piece of meat placed near

a toad may attract flies, and the toad may be observed while catching

them, but the motion is so swift as to be almost imperceptible. Live

flies may be put into a glass jar with a toad. Toads do not move about

until twilight, except in cloudy, wet weather. They return to ponds and

brooks in spring at the time for laying eggs. This time for both frogs

and toads is shown by trilling. All frogs, except tree frogs, remain in

or near the water all the year.

[Illustration: FIG. 248.--METAMORPHOSES OF THE FROG, numbered in order.]

Do =eggs hatch= and tadpoles grow more rapidly in a jar of water kept

in a warm place or in a cold place? In pond water or drinking water?

Can the tadpoles be seen to move in the eggs before hatching? When do

the external gills show? (Fig. 248.)

What =parts= may be described in a tadpole? What is the shape of the

tail? _Compare the tadpole with the fish_ as to (1) general shape, (2)

covering, (3) fins, (4) tail, (5) gills.

Do the external =gills= disappear before or after any rudiments of

limbs appear? (6, 7, Fig. 248.) Can you locate the gills after they

become internal? (Fig. 249.)

[Illustration: FIG. 249.--TADPOLE, from below, showing intestine and

internal gills. (Enlarged.)]

In what state of growth are the _legs_ when the tadpole first goes to

the surface to breathe? Which legs appear first? What advantage is

this? What becomes of the tail? Is the tail entirely gone before the

frog first leaves the water? Are tadpoles habitually in motion or at

rest?

Is the =intestine= visible through the skin? (Fig. 249.) Is it straight

or coiled? Remembering why some fish have larger intestines than

others, and that a cow has a long intestine and a cat a short one,

state why a tadpole has a relatively longer intestine than a frog.

=Compare= the mouth, jaws, eyes, skin, body, and habits of _tadpole and

frog_.

FROGS

Prove that frogs and toads are _beneficial to man_. Did you ever know

of a frog or toad destroying anything useful, or harming any one,

or causing warts? How many pupils in class ever had warts? Had they

handled frogs before the warts came? Frogs are interesting, gentle,

timid animals. Why are they repulsive to some people?

=Environment.=--_Where are frogs found_ in greatest numbers? What

occurs when danger threatens them? What _enemies_ do they have? What

color, or tint, is most prominent on a frog? Does the color “mimic”

or _imitate_ its surroundings? What is the color of the under side of

the body? (Fig. 250.) Why is there greater safety in that color? What

enemies would see water frogs from below? Do tree frogs mimic the bark?

The leaves?

Can a _frog stay under water_ for an indefinite time? Why, or why not?

What part of a frog is above the surface when it floats or swims in a

tub of water? Why? Do frogs croak in the water or on the bank? Why do

they croak after a rain? Do toads croak?

Are the _eggs_ laid in still or flowing water? In a clear place or

among sticks and stems? Singly, or in strings or in masses? (Fig.

248.) Describe an egg. Why do frogs dig into the mud in autumn in cold

climates? Why do they not dig in mud at the bottom of a pond? Why is

digging unnecessary in the Gulf states?

Describe the =position= of the frog when still (Fig. 250). What

advantage in this position? Does the frog use its fore legs in swimming

or jumping? Its hind legs? How is the frog fitted for jumping? Compare

it in this respect with a jumping insect; a jumping mammal. How is it

fitted for swimming? Is the general build of its body better fitted for

swimming or jumping? How far can a frog jump?

[Illustration: FIG. 250.--PAINTED FROG (_Chorophilus ornatus_), of

Mexico.]

=External Features.=--The frog may be said to have two _regions in

its body_, the head and trunk. A neck hardly exists, as there is only

one vertebra in front of the shoulders (Fig. 252), although most

vertebrates have seven neck (cervical) vertebræ. There are no tail

(caudal) vertebræ, even in the tadpole state of frogs and toads.

The _head_ appears triangular in shape when viewed from what direction?

The head of a frog is more pointed than the head of a toad. Is the

skull a closed case of broad bones or an open structure of narrow

bones? (Fig. 252.)

Describe the _mouth_. Observe the extent of the mouth opening (Fig.

251). Are _teeth_ present in the upper jaw? The lower jaw? Are the

teeth sharp, or dull? Does the frog chew its food? Is the _tongue_

slender or thick? (Fig. 251.) Is it attached to the front or the back

of the mouth? In what direction does the free end extend when the

tongue lies flat? Is the end pointed or lobed? How far out will the

tongue stretch? For what is it used? Why is it better for the teeth to

be in the upper jaw rather than in the lower jaw? That the teeth are of

little service is shown by the fact that the toad with similar habits

of eating has no teeth. Will a toad catch and swallow a bullet or

pebble rolled before it? The toad is accustomed to living food, hence

prefers a moving insect to a still one.

[Illustration: FIG. 251.--HEAD OF FROG.]

=The Senses.=--Compare the _eyes_ with the eyes of a fish in respect to

position and parts. Are the eyes protruding or deep-set? Touch the eye

of a live frog. Can it be retracted? What is the shape of the pupil?

The color of the iris? Is the eye bright or dull? What probably gave

rise to the superstition that a toad had a jewel in its head? Is there

a third eyelid? Are the upper and lower eyelids of the same thickness?

With which lid does it wink? Close its eye?

Observe the large oval _ear_ drum or tympanum. What is its direction

from the eye? (Fig. 251.) The mouth? Is there a projecting ear? Does

the frog hear well? What reason for your answer? As in the human ear,

a tube (the Eustachian tube) leads from the mouth to the inner side of

the tympanum.

How many _nostrils_? (Fig. 251.) Are they near together or separated?

Large or small? A bristle passed into the nostril comes into the mouth

not far back in the roof. Why must it differ from a fish in this?

How do the _fore and hind legs_ differ? How many toes on the fore

foot or hand? On the hind foot? On which foot is one of the toes

rudimentary? Why is the fore limb of no assistance in propelling the

body in jumping? Do the toes turn in or out? (Fig. 250.) How does

the frog give direction to the jump? What would be the disadvantage

of always jumping straight forward when fleeing? Which legs are more

useful in alighting?

[Illustration: FIG. 252.--SKELETON OF FROG.]

=Divisions of the Limbs.=--Distinguish the upper arm, forearm, and hand

in the fore limb (Figs. 252 and 253). _Compare with skeleton of man_

(Fig. 399). Do the arms of a man and a frog both have one bone in the

_upper arm_ and two in the _forearm_? Both have several closely joined

bones in the _wrist_ and five separate bones in the _palm_. Do any of

the frog’s fingers have three joints? _Compare also the leg of man_and

the hind leg of the frog (Figs. 253 and 399). Does the _thigh_ have one

bone in each? The shank of man has two bones, shin and splint bone. Do

you see a groove near the end in the shank bone of a frog (Fig. 252),

indicating that it was formed by the union of a shin and splint bone?

The first two of the five bones of the ankle are elongated, giving the

hind leg the appearance of having an extra joint (Fig. 253). The foot

consists of six digits, one of which, like the thumb on the fore limb,

is rudimentary. The five developed toes give the five digits of the

typical vertebrate foot. Besides the five bones corresponding to the

instep, the toes have two, three, or four bones each. How is the hind

foot specialized for swimming? Which joint of the leg contains most

muscle? (Fig. 254.) Find other bones of the frog analogous in position

and similar in form to bones in the human skeleton.

[Illustration: FIG. 253.--SKELETON OF FROG.]

[Illustration: FIG. 254.--LEG MUSCLES OF FROG.]

Is the =skin= of a frog tight or loose? Does it have any appendages

corresponding to scales, feathers, or hair of other vertebrates? Is the

skin rough or smooth? The toad is furnished with glands in the skin

which are sometimes swollen; they form a bitter secretion, and may be,

to some extent, a protection. Yet birds and snakes do not hesitate to

swallow toads whole. Show how both upper and under surfaces of frog

illustrate protective coloration.

All batrachians have large and _numerous blood vessels in the skin_ by

which gases are exchanged with the air, the skin being almost equal to

_a third lung_. That the skin may function in this way, it must not

become dry. Using this fact, account for certain habits of toads as

well as frogs.

If a frog is kept in the dark or on a dark surface, _its skin will

become darker_ than if kept in the light or on a white dish. Try

this experiment, comparing two frogs. This power of changing color

is believed to be due to the diminution in size of certain pigment

cells by contraction, and enlargement from relaxation. This power is

possessed to a certain degree not only by batrachians but also by many

fishes and reptiles. The chameleon, or green lizard of the Gulf states,

surpasses all other animals in this respect (Fig. 280). What advantage

from this power?

[Illustration: FIG. 255.--DIGESTIVE CANAL OF FROG.

_Mh_, mouth; _Z_, tongue pulled outward; _S_, opening to larynx; _Oe_,

gullet; _M_, stomach; _D_, intestine; _P_, pancreas; _L_, liver; _G_,

gall bladder; _R_, rectum; _Hb_, bladder; _Cl_, cloaca; _A_, vent.]

=Digestive System.=--The large mouth cavity is connected by a short

throat with the gullet, or esophagus (Fig. 255). A slit called the

glottis opens from the throat into the lungs (Fig. 255). Is the gullet

long or short? Broad or narrow? Is the stomach short or elongated? Is

the division distinct between the stomach and gullet, and stomach and

intestine? Is the liver large or small? Is it simple or lobed? The

pancreas lies between the stomach and the first bend of the intestines

(Fig. 255). What is its shape? A bile duct connects the liver with

the small intestine (_Dc_, Fig. 255). It passes through the pancreas,

from which it receives several pancreatic ducts. After many turns, the

small intestine joins the large intestine. The last part of the large

intestine is called the rectum (Latin, straight). The last part of the

rectum is called the cloaca (Latin, a drain), and into it the ducts

from the kidneys and reproductive glands also open. The kidneys are

large, elongated, and flat. They lie under the dorsal wall. The urinary

bladder is also large. Does the salamander have a similar digestive

system? (Fig. 256.) Why are the liver and lungs (Fig. 256) longer in a

salamander than in a frog?

[Illustration: FIG. 256.--ANATOMY OF SALAMANDER.

_1a_, heart; _2_, lungs; _3a_, stomach; _3b_, intestine; _3c_, large

intestine; _4_, liver; _8_, egg masses; _10_, bladder; _11_, vent.]

=Respiration.=--How many _lungs_? Are they simple or lobed? (Fig.

256.) A lung cut open is seen to be baglike, with numerous ridges on

its inner surface. This increases the surface with which the air may

come in contact. In the walls of the lungs are numerous capillaries.

Does the frog _breathe with mouth open or closed_? Does the frog have

any ribs for expanding the chest? What part of the head expands and

contracts? Is this motion repeated at a slow or rapid rate? Regularly

or irregularly? There are valves in the nostrils for opening and

closing them. Is there any indication of opening and closing as the

throat expands and contracts? The mouth and throat (pharynx) are filled

with air each time the throat swells, and the exchange of gases (which

gases?) takes place continually through their walls and the walls of

the lungs. At intervals the air is forced through the glottis into the

lungs. After a short time it is expelled from the lungs by the muscular

abdominal walls, which press upon the abdominal organs, and so upon the

lungs. Immediately the air is forced back into the lungs, so that they

are kept filled. In some species the lungs regularly expand at every

second contraction of the throat. This is shown by a slight outward

motion at the sides. Does the motion of the throat cease when the frog

is under water? Why would the frog be unable to breathe (except through

the skin) if its mouth were propped open? Why does the fact that the

breathing is so slow as to almost cease when hibernating, aid the frog

in going through the winter without starving? (Chap. I.) Why must frogs

and toads keep their skins moist? Which looks more like a clod? Why?

=The Heart and Circulation.=--What is the shape of the heart? (Fig.

257.) Observe the two auricles in front and the conical ventricle

behind them. The great arterial trunk from the ventricle passes

forward beyond the auricles; it divides into two branches which turn

to the right and left (Fig. 257). Each branch immediately subdivides

into three arteries (Fig. 257), one going to the head, one to the

lungs and skin, and a third, the largest, passes backward in the

trunk, where it is united again to its fellow. (Colored Fig. 2.)

Both of the pulmonary veins, returning to the heart with pure

blood from the lungs, empty into the left auricle. Veins with the

impure blood from the body empty into the right auricle. Both the

auricles empty into the ventricles, but the pure and impure blood

are prevented from thoroughly mixing by ridges on the inside of the

ventricle. Only in an animal with a four-chambered heart does pure

blood from the lungs pass unmixed and pure to all parts of the body,

and only such animals are warm-blooded. The purer (_i.e._ the more

oxygenated) the blood, the greater the oxidation and warmth.

The red corpuscles in a frog’s _blood_ are oval and larger than those

of man. Are all of them nucleated? (Fig. 258.) The flow of _blood_ in

the web of a frog’s foot is a striking and interesting sight. It may

be easily shown by wrapping a small frog in a wet cloth and laying it

with one foot extended upon a glass slip on the stage of a microscope.

[Illustration: FIG. 257.--PLAN OF FROG’S CIRCULATION.

Venous system is black; the arterial, white. _AU_, auricles; _V_,

ventricle; _L_, lung; _LIV_, liver. Aorta has one branch to right,

another to left, which reunite below. Right branch only persists in

birds, left branch in beasts and man.]

[Illustration: FIG. 258.--FROG’S BLOOD (magnified 2500 areas). Red

cells oval, nucleated, and larger than human blood cells. Nuclei of two

white cells visible near center. (Peabody.)]

[Illustration: FIG. 259.--BRAIN OF FROG.]

[Illustration: FIG. 260.--NERVOUS SYSTEM OF FROG.]

The =brain= of the frog (Fig. 259) is much like that of a fish (Fig.

224). The _olfactory_, _cerebral_, and _optic lobes_, _cerebellum_

and _medulla_ are in the same relative position, although their

relative sizes are not the same. Compared with the other parts,

are the olfactory lobes more or less developed than in a fish? The

cerebral hemispheres? The optic lobes? The cerebellum? There is a

cavity in the brain. It is readily exposed on the under surface of

the medulla by cutting the membrane, which is there its only covering

(Fig. 259).

[Illustration: FIG. 261.--Position of legs in tailless (_A_) and tailed

(_B_) amphibian.]

[Illustration: FIG. 88.--LENGTHWISE SECTION OF MALE CRAWFISH.