SECTION II.

PROTOZOA.

THE Protozoa are the very lowest forms of animal existence, the

beginning and dawn of living things. They first appear as minute

shapeless particles of semi-fluid sarcode moving on the surface of the

waters. The pseudopodia, or false feet, with which they move, are merely

lobes of their own substance which they project and retract. In

creatures of a somewhat higher grade the form is definite, the

pseudopodia, numerous and filamental, serving for locomotion and

catching prey; and from the resemblance they bear to the slender roots

of plants are called Rhizopods.[3] The microscopic organisms possessing

these means of locomotion and supply, are of incalculable multitudes,

and of innumerable forms. Thus the waters, as of old, still ‘bring forth

abundantly the moving creature that hath life;’ in them the lowest types

of the two great kingdoms have their origin, yet they are diverse in the

manifestation of the living principle, that slender but decided line

which separates the vegetable from the animal Amœba.

CLASS I.—RHIZOPODA.

The Amœba, which is the simplest of the group, is merely a mass of

semi-fluid jelly, ‘changing itself into a greater variety of forms than

the fabled Proteus, laying hold of its food without members, swallowing

it without a mouth, digesting it without a stomach, appropriating its

nutritious material without absorbent vessels or a circulating system,

moving from place to place without muscles, feeling (if it has any power

to do so) without nerves, multiplying itself without eggs, and not only

this, but in many instances forming shelly coverings of a symmetry and

complexity not surpassed by those of any testaceous animal.’

[Illustration: Fig. 86. Amœba princeps.]

Such is the description given by Dr. Carpenter of the Amœba and its

allies. The Amœba princeps, which is the type of the naked group, fig.

86, is merely a shapeless mass of semi-fluid sarcode, coated by a soft,

pellucid and highly contractile film, called diaphane by Mr. W. J.

Carter, and in many forms of Amœba the whole is inclosed in a

transparent covering. It is in the interior semi-fluid sarcode alone,

that the coloured and granular particles are diffused, on which the hue

and opacity of the body depend, for the ectosarc or external coat is

transparent as glass. These creatures, which vary in size from the

1/2800 to the 1/70 of an inch in diameter, are found in the sea, but

chiefly in ponds inhabited by fresh-water plants. They move irregularly

over the surface of the water, slowly and continually changing their

form by stretching out portions of their gelatinous mass in blunt

finger-like extensions, and then drawing the rest of it into them; thus

causing the whole mass to change its place. Before it protrudes these

pseudopodia or false feet, there is a rush of the internal semi-fluid

matter to the spot, due to the highly contractile power of the diaphane,

which is often so thin and transparent as to be scarcely perceptible.

When the creature in its progress meets with a particle of food, it

spreads itself over it, draws it into its mass, within which a temporary

hollow or vacuole is made for its reception; there it is digested, the

refuse is squeezed out through the external surface; the nutritious

liquid that is left in the vacuole seems to be dispersed in the sarcode,

for the vacuole disappears. An Amœba often spreads itself over a Diatom,

draws it into a vacuole newly made to receive and digest it; the

siliceous shells of the diatom are pushed towards the exterior, and are

ultimately thrust out; then the vacuole disappears, either immediately

or soon after. These improvised stomachs are the earliest form of a

digestive system.

Besides the vacuoles of which there may be several at a time, the slow

and nearly rhythmical pulsations of a vesicle containing a subtle fluid

may be seen, which changes its position in the interior of the sarcode

with every motion of the Amœba. It gradually increases in size, then

diminishes to a point, and as some of the digestive vacuoles nearest the

surface of the animal are observed to undergo distension when the

vesicle contracts, and to empty themselves gradually as it fills, Dr.

Carpenter thinks it can hardly be doubted that the function of the

vesicle is to maintain a continual movement of nutritious matter, among

a system of channels and vacuoles excavated in the substance of the

body. It is the first obscure rudiment of a circulating system.

In all the Amœbæ the semi-fluid sarcode, with the numerous bodies

suspended in it, rotates at a varied rate within the pellucid coat; a

motion presumed to be for respiration, that is to exchange carbonic acid

gas for oxygen, so indispensable for animal life.[4]

Although like other animals, the Amœba cannot change inorganic into

organic matter, as the vegetable Amœba can do, these two Protozoa are

similar in one mode of reproduction; for portions of the animal Amœba or

even one of the pseudopodia separate from the gelatinous mass, move to a

little distance on the surface of the water, and become independent

Amœbæ.

With a high microscopic power, many bodies besides the digesting

vacuoles and pulsating vesicles may be seen imbedded in the sarcode of

the Amœba princeps; namely, coloured molecules, granules, fat-globules,

and nuclei. All these bodies were seen by Mr. Carter, in certain Amœbina

he found at Bombay, together with what he believed to be female

reproductive cells, and motile particles similar to spermatozoids, or

male fertilizing particles.

[Illustration: Fig. 87. Actinophrys sol.—A, ordinary form; B, act of

division or conjugation; C, process of feeding; D, discharge of fæcal

matter, _a_ and _b_; _o_ _o_, contractile vesicles.]

The Actinophrys, a genus of the order Radiolaria, differs from the Amœba

princeps in having a definite nearly spherical form with slender

root-like filamental pseudopodia radiating from its surface in all

directions as from a centre. They taper from the base to the apex, and

sometimes end in knobs like a pin’s head, but vary much in length and

number, and can be extended and retracted till they are out of sight.

They are externally of a firmer substance than the sarcode of the body,

which is merely a viscid fluid inclosed in a pellucid film. The

Actinophrys sol, which is the type of the genus, is a sphere of from

1/1300 to 1/650 of an inch in diameter, with slender contractile

filaments the length of its diameter extending from its surface as rays

from the sun. It can draw them in and flatten its body so as to be

easily mistaken for an Amœba. This creature, which is common in

fresh-water pools where aquatic plants are growing and even in the sea,

has little power of moving about like the Amœba; it depends almost

entirely on its pseudopodia for food. They have an adhesive property,

for when any animalcule or diatom comes in contact with one of them,

they adhere to it; the filament then begins to retract, and as it

shortens the adjacent filaments apply their points to the captive,

enclose it, coalesce round it, the whole is drawn within the surface of

the Actinophrys, the captive is imbedded in the sarcode mass, and passes

into a vacuole where it is digested, and then the pseudopodia thrust out

the undigested matter by a process exactly the reverse of that by which

the food was taken in (D fig. 87). The pseudopodia are believed by

Professor Rupert Jones to have the power of stunning their prey, for if

an animalcule be touched by one of them, it instantly becomes

motionless, and does not resume its activity for some time. The

pulsations of the contractile vesicle are very regular, and its duty is

the same as in the Amœba princeps.

The Actinophryna are propagated like the lowest vegetables by gemmation

and conjugation, shown in B fig. 87; moreover Mr. Carter saw the

production of germ-cells and motile particles in the Actinophrys exactly

after the mode already described in the Amœba.

Mr. Carter mentions an instance in which the Actinophrys sol showed what

may possibly be a certain degree of instinct. An individual was in the

same vessel with vegetable cells charged with particles of starch; one

of the cells had been ruptured and a little of the internal matter was

protruded through the crevice. The Actinophrys came, extracted one of

the starch-grains, and crept to a distance; it returned, and although

there were no more starch-grains in sight, the creature managed to take

them out from the interior of the cell one by one, always retiring to a

distance and returning again, showing that it knew its way back, and

where the starch-grains were to be found. On another occasion Mr. Carter

saw an Actinophrys station itself close to the ripe spore cell of a

plant, and as the young zoospores came out one after another, the

Actinophrys caught every one of them even to the last and then retired

to a distance as if instinctively conscious that no more remained. Like

Amœbæ these animals select their food, but notwithstanding the superior

facility and unfailing energy with which they capture prey larger and

more active than themselves, they are invariably overcome even by a very

small Amœba which they avoid if possible. When they come into contact

the Amœba shows unwonted activity, tries to envelope the Actinophrys

with its pseudopodia, but failing to capture the whole animal it tears

out portions and conveys them to improvised vacuoles to be digested. Dr.

Wallich mentions that he had seen nearly the half of a large Actinophrys

transferred piecemeal to the interior of its enemy, where it was quickly

digested.

_Fig. 88, p. 19._

[Illustration: ACANTHOMETRA BULBOSA.]

As every part of the body of the Actinophrys is equally capable of

performing the part of nutrition, respiration, and circulation; and as

in the absence of muscles and nerves they may be presumed to have no

consciousness, the marks of apparent intelligence can only be attributed

to a kind of instinct, and their motions to the vast inherent

contractility of the sarcode and its enclosing film, which is also the

case with the Amœbæ.

The Acanthometræ (see fig. 88, Acanthometra bulbosa) are all marine

animals; their skeleton consists of a number of long spicules which

radiate from a common centre, tapering to their extremities. These

spicules are traversed by a canal with a furrow at the base through

which groups of pseudopodia enter, emerging at the apex. Besides, there

are a vast number of pseudopodia not thus enclosed, resembling those of

the Actinophrys in appearance and action. The body is spherical, and

occupies the spaces left between the bases of the spicules. The exterior

film covering the body seems to be more decidedly membranaceous than

that of the Actinophrys, but it is pierced by the pseudopodia which

radiate through it. This exterior film itself is enclosed in a layer of

a less tenacious substance, resembling that of which the pseudopodia are

formed. There is a species of Acanthometra (echinoides) extremely common

in some parts of the coast of Norway, which, to the naked eye, resembles

merely a crimson point.

_Fig. 90, p. 20._

[Illustration: DICTYOPODIUM TRILOBUM.]

[Illustration: Fig. 91. Podocyrtis Schomburgi.]

The Polycystina are an exceedingly numerous and widely dispersed group

of siliceous rhizopods. They are inhabitants of the deep waters, having

been brought up from vast depths in the Atlantic and Pacific oceans.

Their bodies are inclosed in siliceous shells, which have either the

form of a thin hollow sphere perforated by large openings like windows,

or of a perforated sphere produced here and there into tubes, spines,

and a variety of singular projections: so they have many varied but

beautiful microscopic forms. The animal which inhabits these shells is a

mouthless mass of sarcode, divided into four lobes with a nucleus in

each and covered with a thick gelatinous coat. It is crimson in the

Eucyrtidium and Dictyopodium trilobum of Haeckel (figs. 89 and 90): in

others, as the Podocyrtis Schomburgi, it is olive brown with yellow

globules (fig. 91). These creatures extend themselves in radiating

filaments through the perforations of their shells in search of food,

like their type the Actinophrys sol, to whose pseudopodia the filaments

are perfectly similar in form, isolation, and in the slow movements of

granules along their borders. The Polycystine does not always fill its

shell, occasionally retreating into the vault or upper part of it, as in

the Eucyrtidium (fig. 89, frontispiece to vol. i.). Sometimes the shell

is furnished with radiating elongations, as in the Dictyopodium trilobum

(fig. 90). In both of these shells the animal consists of four crimson

lobes. These beautiful microscopic organisms are found at present in the

Mediterranean, in the Arctic and Antarctic seas, and on the bed of the

North Atlantic. They had been exceedingly abundant during the later

geological periods; multitudes are discovered in the chalk and marls in

Sicily, Greece, at Bermuda, at Richmond in Virginia and elsewhere; in

all 282 different fossil forms have been described, grouped in 44

genera.

_Fig. 92, p. 21._

[Illustration: AULOCANTHA SCOLYMANTHA.]

_Fig. 93, p. 21._

[Illustration: ACTINOMMA DRYMODES.]

_Fig. 94, p. 21._

[Illustration: HALIOMMA ECHINASTER.]

In certain Polycystina, the perforations of the shell are so large and

so close together, that the sarcode body of the animal appears to be

covered by a siliceous net. This connects them with the Thalassicollæ,

minute creatures found passively floating on the surface of the sea. Th.

morum, which is one of the most simple of the few forms known, has a

spherical body of sarcode covered with a siliceous net, through which

the pseudopodia radiate in all directions, as in the Actinophrys, but it

is studded at regular distances with groups of apparently radiating

siliceous spicules.

The Aulocantha scolymantha (fig. 92), found by M. Haeckel in the

Mediterranean, may be taken as an example of the most general form of

the Thalassicolla. The siliceous skeleton of some of the Radiolaria

resembles the Chinese ivory toy of ball within ball. That of the

Actinomma drymodes (fig. 93) consists of three perforated concentric

spheres, with six strong spicules attached to the outer surface,

perpendicular to one another and prolonged in the interior to the

central sphere. Hundreds of finer bristle-like spicules radiate from the

surface. The animal is chiefly contained in the central sphere, and from

it a perfect forest of fine, long pseudopodia radiate in thick tufts

through the apertures of the exterior sphere.

The skeleton of the Haliomma (fig. 94) consists of only two concentric

spheres. In many species of Haliomma and Actinomma the animals are of

the most vivid vermilion or purple colour. Little or nothing is known of

the reproduction of these microscopic organisms.

The Actinomma drymodes and the Haliomma are two of the most beautiful

microscopic rhizopods discovered by M. Haeckel.

There is a family of fresh-water testaceous rhizopods of which one group

secretes its shell and the other builds it. The horny shell secreted by

the group of the Arcella presents various degrees of plano-convexity,

the convexity in some cases amounting to a hemisphere. They rarely, if

ever, have mineral matter on their surface, which is studded with

regular but very minute hexagonal reticulations. The aperture or mouth

of the shell is small, and invariably occupies the centre of the plane

surface, its margins being more or less inverted. The form of the shell

is exceedingly varied, sometimes it even has horns indefinite in number,

sometimes symmetrical, sometimes not; when its test or covering becomes

too small for its increasing size, it quits it, and secretes a new one.

The filamental pseudopodia proceed from the mouth of the shell only, and

by means of these it creeps about on its mouth in search of food.

[Illustration: Fig. 95. Simple Rhizopods.—A, B, Difflugiæ; C, D,

Arcellæ.]

The Difflugia build their own shells, which are usually truncated

spheres, ovate, or sometimes elongated into the form of a pitcher or

flask. The most minute recognisable of these shells is about the 1/1000

of an inch in diameter, but they are constructed with the most perfect

regularity. The Difflugia pyriformis or symmetrica has the form of an

egg with an aperture at the small end. It is entirely made up of

rectangular hyaline plates, arranged with the greatest regularity in

consecutive transverse and longitudinal rows, the smaller ones being at

the extremities, while the larger ones occupy the central and widest

portion of the structure. The inhabitant of this abode is an Amœba with

a sarcode body covered with a thin film, from whence it sends off

pseudopodia through the mouth of its shell. The Difflugia is propagated

by conjugation, but before that takes place it becomes densely charged

with chlorophyll-cells and starch-grains. The former disappear during

the subsequent changes, and are replaced by a mass of colourless cells

full of granules which are supposed to be the elements of a new

generation. The embryo or earliest form is a minute truncated sphere,

but the animal builds up its habitation very much according to local

circumstances.

The greater number of the Difflugiæ secrete a substance which forms a

smooth layer in the interior, which the animal covers with sarcode from

its mouth, and then it drags itself with its pseudopodia to the

particles which it selects, and they adhere to it. The particles

selected are invariably mineral matter. ‘The selective power is carried

to such an extent that colourless particles—sometimes quartzose,

sometimes felspathic, sometimes micaceous—are always chosen.’ ‘The

particles seem to be impacted into the soft matter, laid on the exterior

in the same way that a brick is pressed into the yielding mortar, and

that too, in so skilful a manner as to leave the smallest possible

amount of vacant area; whilst in the specimens of Difflugia in which

tabular or micaceous particles are used, they are sometimes disposed

with such nicety that there is no overlapping, but the small fragments

are placed so as to occupy the space left between the larger ones. These

excellent architects seem to know that in the valves of the Diatoms are

combined the properties best suited to their wants, that is,

transparency and form, capable of being easily arranged.’

Both the Difflugia and Arcella are Amœbæ in the strictest sense of the

word; their bodies consist of sarcode, which sends out finger-like lobes

from the mouth of the shell at one end, while the other end has an

adhesive property, which fixes it to the bottom. The nucleus and

contractile vesicles are identical in character with those of the Amœbæ,

and exhibit the same tendency to subdivision at certain periods of the

creature’s history that is witnessed on a large scale in the Amœba

proper; and the reproductive process is the same.[5]

The Difflugiæ are found in rivulets and pools containing aquatic plants;

the condition of the water and the nature of the soil have a great

influence on the form of their shell.

The Euglyphæ is the third group of fresh-water rhizopods. They are

extremely minute, and there are no mineral particles whatever on their

shells, the axes of which do not coincide with the aperture. The

interior of the animal is like that of the Arcella and Difflugia, but it

differs from them in as much as the pseudopodia and ectosarc, or

external coat, are finely granular, and the whole mass of the body

possesses a decided degree of adhesive viscidity. The pseudopodia are

filiform, tapering, radiating, and readily coalesce; and ‘as if to

compensate for the restricted power of locomotion, compared with that of

the Amœba proper, the pseudopodia of the Euglyphæ are much more active.

The rapidity with which they admit of being projected outwards, and

withdrawn into the shell, is unequalled in any other form, presenting

the most wonderful example of inherent contractility in an amorphous

animal substance, that is to be met with in either of the great organic

kingdoms.’[6]

The order Reticularia, with a very few exceptions, are animals dwelling

in calcareous microscopic shells, and differing essentially in

constitution from all the preceding Rhizopods. The ectosarc or

surface-layer of the sarcode in the Amœba and Actinophrys has so much

consistence, that their pseudopodia, which are derived from it, have a

decidedly firm outline and never coalesce; whereas in the order

Reticularia, the sarcode is merely a semi-fluid protoplasm or colourless

viscid fluid, without the smallest surface-layer or film, so that their

pseudopodia possess no definiteness either in shape, size or number.

Sometimes they are cylindrical, and sometimes form broad flat bands,

whilst they are often drawn into threads of such extreme tenuity, as to

require a high magnifying power to discern them. They coalesce and fuse

into each other so freely and so completely when they meet, that no part

of their substance can be regarded as having more than a viscous

consistence. Their margins are not defined by continuous lines, but are

broken by granules irregularly disposed among them, so that they appear

as if torn; and these granules, when the animal is in a state of

activity, are in constant motion, passing along the pseudopodia from one

end to the other, or passing through the connecting threads of this

animated network from one pseudopodium to another, with considerable

rapidity, analogous to the movement of the particles in the cells of the

hairs of the Tradescantia and other plants.[7]

The sarcode body of the Gromiæ is inclosed in a yellowish brown horny

envelope or test of an oval shape, with a single round orifice of

moderate size, through which the pseudopodia extend into the surrounding

water, some forms of the animal being marine, others inhabitants of

fresh water. When the animal is at rest all is drawn within the test,

and when its activity recommences, single fine threads are put out which

move about in a groping manner until they find some surface to which

they may attach themselves. When fixed, sarcode flows into them so that

they rapidly increase in size, and then they put forth finer

ramifications, which diverging come in contact with those from other

stems, and by mutual fusion form bridges of connection between the

different branching systems; for the protoplasm spreads over the

exterior of the test, and from it pseudopodia extend and coalesce,

wherever they meet, so that the whole forms a living network, extending

to a distance of six or eight times the length of the body. Fig. 96

represents the Gromia oviformis with its pseudopodia extended.

[Illustration: Fig. 96. Gromia oviformis.]

In the Gromiæ the granular particles in the semi-fluid protoplasm are in

constant motion. In the finer filaments there is but one current, and a

particle may be seen to be carried to the extremity, and return again

bringing back with it any granules that may be advancing; and should

particles of food adhere to the filament they take part in the general

movement. In the broader filaments two currents carrying particles pass

backwards and forwards in opposite directions at the same time, and the

network in which these motions are going on is undergoing continual

changes in its arrangements. New filaments are put forth sometimes from

the midst of the ramifications, while others are retracted; and

occasionally a new centre of radiation is formed at a point where

several threads meet. The food consists of diatoms and morsels of

vegetable matter; but the Gromiæ have no vent, so that the indigestible

matter collects in a heap within them. However, as the form of the test

is such that the animal cannot increase its size, it leaves it when it

becomes too small for its comfort and forms another, and it is supposed

to get rid of the effete matter at the same time. The Gromiæ have no

nucleus or contractile vesicle.

CLASS II.—FORAMINIFERA.

The geological importance of the Foraminifera, their intrinsic beauty,

the prodigious variety of their forms, their incredible multitude, and

the peculiarity of their structure, have given these microscopic

organisms the highest place in the class of Rhizopods. The body of these

animals consists of a perfectly homogeneous sarcode or semi-fluid

protoplasm, showing no tendency whatever to any film or surface-layer.

It is inclosed in a shell; and the only evidence of vitality that the

creature gives, is a protrusion and retraction of slender threads of its

sarcode, through the mouth or pores of the shell, or through both

according to its structure. Fig. 97 shows some of their forms.

By far the greater number of the Foraminifera are compound or

many-chambered shells. When young, the shell has but one chamber,

generally of a globular form; but as the animal grows, others are

successively added by a kind of budding in a definite but different

arrangement for each order and genus of the class. When the creature

increases in size, a portion of its semi-fluid sarcode projects like a

bud from the mouth of its shell. If it be of the one-chambered kind, the

bud separates from its parent before the shelly matter which it secretes

from its surface consolidates, and a new individual is thus produced.

But if the primary shell be of the many-chambered kind, the shelly

secretion consolidates over the sarcode projection which thus remains

fixed, and the shell has then two chambers, the aperture in the last

being the mouth, from which, by a protrusion of sarcode, a third chamber

may be added, the new chamber being always placed upon the mouth of its

predecessor, a process which may be continued indefinitely, the mouth of

the last segment being the mouth of the whole shell.

[Illustration: Fig. 97. Various forms of Foraminifera:—A, Oolina

claxata; B, Nodosaria rugosa; C, Nodosaria spinicosta; D Cristellaria

compressa; E, Polystomella crispa; F, Dendritina elegans; G, Globigerina

bulloïdes; H, Textularia Mayeriana; I, Quinqueloculina Bronniana.]

By this process an ovate shell with a mouth at one extremity may have a

succession of ovate chambers added to it, each chamber being in

continuity with its predecessor so that the whole shell will be straight

and rod-like, the last opening being the mouth. If the original shell be

globular, and if all the successive gemmæ given out be equal and

globular, the shell covering and uniting them will be like a number of

beads strung upon a straight wire. Sometimes the successive gemmæ

increase in size so that each chamber is larger than the one which

precedes it; in this case the compound shell will have a conical form,

the primary shell being the apex, and the base the last formed, the

aperture of which is the mouth of the whole shell; a great many

Foraminifera have this structure. The spiral form is very common and

much varied. A series of chambers increasing in size may coil round a

longitudinal axis, like the shell of the snail; but if each of the

successive chambers, instead of being developed exactly in the axis of

its predecessor, should be directed a little to one side, a curved

instead of a straight axis would be the result; there is a regular

gradation of forms of Foraminifera between these two types. The

convolutions are frequently flat and in one plane, but the character of

the spiral depends upon the successive enlargement or not of the

consecutive chambers; for when they open very wide and increase in

breadth, every whorl is larger than that which it surrounds; but more

commonly there is so little difference between the segments after the

spiral has made two or three turns, that the breadth of each whorl

scarcely exceeds that which precedes it.

However varied the forms may be, the mouth of the last shell is the

mouth of the whole, either for the time being or finally. For all the

chambers are connected by narrow apertures in the partitions between

them. Each chamber is occupied by a segment of the gelatinous sarcode

body of the animal, and all the segments are connected by sarcode

filaments passing through the minute apertures in the partitions between

the chambers, so that the whole constitutes one compound creature.

Although the character and structure assumed by the semi-fluid bodies of

the known Foraminifera have been determined in most cases with admirable

precision, it is still thought advisable to arrange them according to

the substance of the shell: consequently they form three natural orders;

namely, the Porcellanous or imperforate, which have calcareous shells

often so polished and shining that they resemble porcelain; secondly,

the Arenaceous Foraminifera, consisting of animals which secrete a kind

of cement from their surfaces, and cover themselves with calcareous or

siliceous sand-grains; and lastly, the Vitreous and Perforated order,

which is the most numerous and highly organized of the whole class, has

siliceous shells transparent as glass, but acquires more or less of an

opaque aspect in consequence of minute straight tubes which perforate

the substance of the shell perpendicularly to its surface, and

consequently interfere with the transmission of light.

_Order of Porcellanous Foraminifera._

The Miliolidæ constitute the porcellanous order, which consists of

twelve genera and many species, varying from a mere scale to such as

have chambered shells of complicated structure.

The genus Miliola has minute white shells resembling millet seeds, often

so brilliantly polished that they are perfectly characteristic of the

porcelain family to which they belong. No Foraminifera are better suited

to give an idea of the intimate connection between the shell and its

inhabitant than the Miliola, the fundamental type of this genus. The

shell is a spiral (I, fig. 97), which is made up of a series of half

turns arranged symmetrically on its two sides. Each half turn is longer

and of greater area than that on the opposite side, so that each turn of

the spire has a tendency to extend itself in some degree over the

preceding one, which gives a concave instead of a convex border to the

inner wall of the chamber. The sarcode body of the Miliola consists of

long segments which fill the chambers, connected by threads of sarcode

passing through the tubular constrictions of the shell. As the animal

grows, its pseudopodia extend alternately now from one end, and now from

the other extremity of the spiral, and by them it fixes itself to

seaweeds, zoophytes, and other bodies, for these Foraminifera never

float or swim freely in the water. The genus Miliola is more extensively

diffused than almost any other group of Foraminifera; they are most

abundant between the shore and a depth of 150 fathoms, and are

occasionally brought up from great depths. Beds of miliolite limestone

show to what an extent the Miliola abounded in the seas of the Eocene

period; but the type is traced back to the Lias.

The genus Peneroplis is distinguished by a highly polished opaque white

shell; its typical form is an extremely flat spire of two turns and a

half opening rapidly and widely in the last half whorl. It is strongly

marked by depressed bands which indicate the septa or shelly partitions

between the chambers in the interior. The polished surface of the shell

is striated between and transversely to the bands by parallel

platted-looking folds 1/1400 of an inch apart. But the peculiarity of

this shell and its congeners is, that the partitions between the

chambers in its interior are perforated by numerous isolated and

generally circular pores which in this compressed type are in a single

linear row. Their number depends upon the length of the partition

between the chambers, which increases with the age of the animal and

size of the shell. There is but one pore in each of the consecutive

partitions from the globular centre to the fourth chamber. From the

fourth to the seventh chamber the communication is by two pores; after

this the number is gradually increased to three, four, six, &c., up to

forty-eight, so that the last segment may send out forty-eight

pseudopodia from the mouth of the shell. In its early youth one

pseudopodium appears to have been sufficient to find food for the

animal, but as the shell increased in size and the segments in number, a

greater supply of food was requisite and a greater number of pseudopodia

were necessary to fish for it. Moreover when an addition to the shell is

required the pseudopodia coalesce at their base and form a continuous

segment upon which the new portion of the shell is moulded.

In varieties of the Peneroplis where the spire is less compressed there

are sometimes two rows of pores in the partitions between the chambers.

The Dendritine variety deviates most from that described. It is

characterised by a single large aperture in each partition which sends

out ramifications from its edges. The form of these openings depends

upon that of the spire; when compressed the aperture is linear and less

branched at its edges; but in shells which have a very turgid spire it

is sometimes broader than it is long, and much branched; but these

extremes are connected by a variety of forms. The shells of this variety

of the Peneroplis are strongly marked by the depressed bands and striæ,

as in the Dendritina elegans (F, fig. 97). The segments of the animal

inhabiting these shells must be more intimately connected than in most

of the other Foraminifera; and the pseudopodia sent through these large

apertures out of the mouth of the shell must be comparatively quite a

mass of sarcode. The Dendritinæ are inhabitants of shallow water and

tropical seas, while the other members of the genus Peneroplis abound in

the Red Sea and the seas of other warm latitudes, especially in the zone

of the great laminarian fuci. They do not appear in a fossil state prior

to the beginning of the Tertiary period.

The last whorls of some of the compressed spiral Foraminifera of the

Porcellanous order so nearly encompass all their predecessors, that the

transition from a flat spiral to the Orbitolite with its flat disk of

concentric rings is not so abrupt as might at first appear. The gradual

change may be distinctly traced in the species of the genus Orbiculina.

The exteriors of the shells of the genus Orbitolites have less of the

opaque whiteness than many others of its family. In its simplest form it

is a disk about the 1/500 of an inch in diameter, consisting of a

central nucleus surrounded by from ten to fifteen concentric circular

rings. The surface is usually plane, though sometimes it is concave on

both surfaces in consequence of the rings increasing in thickness

towards the circumference. The rings or zones are distinctly marked by

furrows on the exterior of the shell, and each of these zones is divided

by transverse furrows into ovate elevations with their greatest diameter

transverse to the radius of the disk, so that the surface presents a

number of ovate elevations arranged in consecutive circles round the

central nucleus. The margin of the disk exhibits a series of convexities

with depressions between them; in each of these depressions there is a

circular pore surrounded by a ring of shell: these pores are the only

means the animal possesses of communicating with the water in which it

lives.

[Illustration: Fig. 98. Simple disc of Orbitolites complanatus.]

[Illustration: Fig. 99. Animal of Orbitolites complanatus.]

Fig. 98 is a horizontal section of the simple Orbitolite showing the

internal structure of the disk. A pear-shaped chamber with a

circumambient chamber forms a nucleus which is surrounded by series of

concentric rings of ovate cavities. The chambers of the nucleus and all

the cavities are filled with segments of homogeneous semi-fluid sarcode,

which constitute the body of the animal (fig. 99). The segments in the

rings are connected circularly by gelatinous bands of sarcode extending

through passages which connect the cavities laterally. The segments are

also connected radially by similar sarcode bands, which originate in the

mass of sarcode filling the nucleus, and extend to the pores in the

margin of the disk. The cavities of each zone alternate in position with

those of the zones on each side of it. The animal sends out its

pseudopodia through the marginal pores in search of food, which consists

of Diatoms and Desmidiaceæ; they are drawn in, digested without any

stomach, and the nutritious liquid is conducted by the gelatinous bands

from segment to segment and from zone to zone, even to the innermost

recesses of the shell.

It is supposed that during the growth of the Orbitolite, when the animal

becomes too large for its abode, its pseudopodia coalesce and form a

gelatinous massive coat over the margin of the exterior zone, which

secretes a shelly ring with all its chambers and passages, each ring

being a mere vegetative repetition of those preceding it. That

vegetative property enables the animal to repair its shell or add a part

that is wanting. For, if a small portion of a ring be broken off and

separated from the living animal, it will increase so as to form a new

disk, the want of the central part or nucleus not appearing to be of the

smallest consequence; indeed, the central rings are very often

imperfect. The sarcode of these animals is red, and although the shell

is of a brownish-yellow by transmitted light, it is so translucent that

the red tint is seen through it.

The simple Orbitolite has many varieties. Sometimes it begins its life

as a spiral which changes to a circular disk as it advances in age. It

varies in thickness, and some of its very large varieties may be said to

consist of three disks or stories of concentric chambers and many

marginal pores instead of one. The upper and base stories of concentric

chambers are alike, the intermediate one very different, but the sarcode

segments in all the three are so connected as to form a very complex

compound animal.[8] Different as this structure is from that of the

simple Orbitolite, they are merely varieties of the same species; for it

has been shown by Dr. Carpenter that, although many pass their lives in

the simple one-storied state, they may change into the complex form at

any stage of their growth; and as an equally extensive range of

variation has been proved by Professor Williamson and Mr. Parker to

prevail in other groups of Foraminifera, the tendency to specific

variation seems to be characteristic of that type of animal life, and

consequently the number of distinct species is less than they were

supposed to be.

The Orbitolites are found in the dredgings of all the warmer seas, in

vast multitudes at the Philippine Islands, but those from Australia are

the most gigantic, being sometimes the size and thickness of a shilling.

_Order of Arenaceous Foraminifera._

In the numerous family of Lituolidæ the abode of the animal consists of

a cement mixed with very fine particles of sand with larger ones

imbedded in the surface. The order includes a wide range of forms

divided into three genera, the simplest of which consists of a

cylindrical tube twisted into a spiral gradually increasing in diameter,

and attached to a foreign substance by one of its surfaces. The creature

which lives in it is a uniform cord of sarcode, which sends its

pseudopodia out through a large aperture at the extremity of its tube in

search of food. Although the tube consists of sand imbedded in an

ochreous-coloured cement secreted by the animal, its surface is smooth

as a plastered wall. The spiral tubes of this genus take various forms,

and in some cases are divided into chambers.

The members of the genus Lituola exude from their surfaces a thick coat

of cement with a quantity of siliceous particles roughly imbedded in it,

but in some instances the particles are so uniform in size and shape,

and are so methodically arranged, that the surface resembles a

tesselated pavement. The usual form of the Lituola is a mere string of

oval convex chambers increasing gradually in size, and fixed to shells

and corals by their flat surfaces. In some instances the shells, or

rather the substitutes for shells, take a nautiloid form, and become

detached from the foreign bodies to which they were attached. In the

highest forms of this genus the chambers are divided by secondary

partitions.

The typical form of the genus Valvulina is a three-whorled, three-sided

pyramidal shell, with three chambers in every turn of the spire. The

aperture is large and round, with a valve of smaller size attached by a

tooth of shell to its rim. The creature itself has an exceedingly thin

perforated vitreous shell, covered by an incrustation of calcareous

particles, which so entirely blocks up the perforations that it can only

extend its pseudopodia through the mouth of its shell.

_Order of Vitreous Foraminifera._

Nearly all the Foraminifera on the British coasts belong to the Vitreous

or Perforated order, which consists of three natural families and many

genera. Their shells are vitreous, hyaline, and generally colourless,

even although the substance of the animal is deeply coloured; in some

species both the animal and its shell are of a rich crimson. The glassy

transparency of the shells would be perfect were they not perforated by

numerous tubes running from the interior of the chambers straight

through the shell, and ending in pores on its surface. According to

microscopic measurement the tubes in the Rotalia, which are the largest,

are on an average the 1/1000 of an inch in diameter, and as they are

somewhat more than that apart, the transparency of the shell appears

between them and gives the surface a vitreous aspect. The pseudopodia of

the animal have been seen to pass through every part of the wall of the

chambers occupied by it; the apertures of the tubuli in this case are

wide enough to permit particles of food to be drawn into the interior of

the shell. But threads of sarcode of extreme tenuity alone could pass

through the tubuli of the Operculina, which are not more than the

1/10000 of an inch in diameter, and the distance between them not much

greater, which gives the shell an opaque appearance. Particles of food

can hardly be small enough to pass through such tubes into the interior

to be digested. Dr. Carpenter, however, is almost certain, from the

manner in which the animal repairs injuries done to its shell, that the

semi-fluid sarcode extends itself at certain times, if not constantly,

over the exterior of the shell, as in the Gromia; and therefore it is by

no means impossible that the digestive process may really be performed

in this external layer, so that only the products of digestion may have

to pass into the portion of the sarcode occupying the body of the shell.

In such many-chambered shells as are pierced by tubuli wide enough to

permit particles of food to be drawn into the interior, each segment of

the animal, being fed within its own chamber, has a life of its own, at

the same time that it shares with all the others in a common life

maintained by food taken in through the mouth of the shell. There are

many instances of this individual life combined with a common life among

the lowest tribes of animals.

Although the Perforated order contains types widely apart, they are

always connected by intermediate forms; but there is no such connection

between the two great natural orders, which are not only separated by

the tubuli in the shell, but in many instances by the structure of the

interior and the corresponding character of the animal.

In the Lagenidæ, which form the first family of the Perforated order,

the vitreous shell possesses great hardness, and is pierced by numerous

small tubuli. It is very thin, and of glossy transparency. The first

four shells in fig. 97 represent some of its forms.

The genus Nodosaria has a very extensive range of forms, from the

elongated structure to the nautiloid spiral, depending upon the relative

proportions and arrangement of the segments. The segments are separated

by constrictions transverse to the axis of growth, or by bands as in the

Nodosaria rugosa, B, fig. 97. It frequently happens that parts of the

shell are not perforated; and there are generally longitudinal ribs

which sometimes have spines projecting from every part of the interior,

as in Nodosaria spinicosta, C, fig. 97.

In the genus Nodosaria, the axis of growth changes from a straight line

to that of a spiral, so that the septa or divisions between the segments

cross the axis obliquely, and the aperture instead of being exactly

central becomes excentric. Between these extremes there is a numerous

series of gradations. The Cristallaria is the highest type; the form is

a nautiloid spiral, more or less compressed (D, fig. 97), of which each

whorl has its chambers extended by winged projections so as to reach the

centre, and entirely encloses the preceding whorl. The number of

chambers in each whorl is much smaller than in most of the nautiloid

spirals, not being more than eight or nine. The divisions are always

strongly marked externally by septal bands, varying in character

according to the species. The margin of the shell runs into a keel,

which is sometimes extended into a knife-edge. Nearly all the Lagena

family are found in the North Atlantic and Mediterranean, especially in

the Adriatic, which is rich in species. In the Nodosaria the cells which

compose the shell have so little connection one with another that they

may be easily detached; which gives reason to believe that the

separation of the parts may be a means of reproduction and dispersion.

The Globigerinidæ are the most numerous family of the perforated series,

and the most remarkable in the history of the existing Foraminifera.

They are distinguished by the coarseness of the perforations in their

shells, and by the crescentic form of the aperture by which the chambers

communicate with each other.

The genus Globigerina consists of a spiral aggregation of globose

segments, which are nearly disconnected from each other although united

by mutual cohesion. The segments are always somewhat flattened against

one another in their planes or junctions, and sometimes the flattening

extends over a pretty large surface as in G, fig. 97. The entire series

of segments shows itself on the upper side, but on the lower side only

the segments forming the latest convolution are prominent; they are

usually four in number, and are arranged symmetrically round a deep

depression or vestibule; the bottom of which is formed by the segments

of the earlier convolutions. In this vestibule each segment opens by a

large crescent-shaped orifice, the several chambers having no direct

communication with each other. The entire shell of the ordinary type may

attain the diameter of about 1/30 of an inch, but it is usually much

smaller; the typical form, however, is subject to very considerable

modifications. In newly formed segments of Globigerina, the hyaline

shell substance is perforated by tubuli varying from 1/10000 to 1/5000

of an inch in diameter, arranged at pretty regular distances; but in

deep seas the surface of the shell is raised by an external deposit into

tubercles or ridges, the orifices of the pores appearing between them.

_Fig. 100, p. 41._

[Illustration: ROSALINA ORNATA.]

Each chamber of the shell is occupied by a reddish-yellow segment of

sarcode, from which pseudopodia are seen to protrude; and it is supposed

that the sarcode body also fills the vestibule, since without such

connecting band it is difficult to understand how the segments which

occupy the separate chambers can communicate with each other, or how new

segments can be budded off. In the Globigerina the slight cohesion gives

reason to believe that the separation of the parts may be a means of

reproduction.

The Rosalina ornata, one of the most beautiful specimens of this group,

and remarkable for the size of its pores, is represented in fig. 100

with its pseudopodia extended, and coalescing in some parts.

The shells of the genus Textularia consist of a double series of

chambers disposed on each side of an axis, so that they look as if they

were mutually interwoven. As the segments for the most part increase

gradually in size, the shell is generally triangular, the apex being

formed of the first segment, and its base of the two last (H, fig. 97).

The aperture is always placed in the inner wall of each chamber, close

to its junction with the preceding segment on the opposite side. In the

compressed shells it is crescent-shaped, but it is semilunar in the less

compressed, and may even be gibbous. The shell is hyaline, with large

pores not very closely set, though in some varieties they are minute and

near to one another. Sometimes the pores open on the surface in deep

hexagonal pits. The older shells are frequently incrusted with large

coarse particles of sand, and some specimens from deep water are almost

covered with fine sand, but with a good microscope the pores may be seen

between them.

The sarcode segments of the animal perfectly correspond in shape and in

alternate arrangement with the segments of the shell, and are connected

by bands of sarcode passing through the crescent-shaped apertures by

which each chamber communicates with that which precedes and follows it.

The Textulariæ are among the most cosmopolitan of Foraminifera; some of

their forms are found in the sands and dredgings from all shores, from

shallow or moderately deep water. In time they go back to the Palæozoic

period.

The Rotalia Beccarii, common on the British coast, affords a good

example of the supplemental skeleton, a structure peculiar to some of

the higher vitreous Foraminifera. It has a rather compressed turbinoid

form with a rounded margin. Its spire is composed of a considerable

number of bulging segments gradually increasing in size, disposed with

great regularity, and with their opposed surfaces closely fitted to each

other. The whole spire is visible on the exterior, with all its

convolutions, and on account of the bulging form of the segments, their

lines of junction would appear as deep furrows along the whole spire,

were they not partly or wholly filled up with a homogeneous

semi-crystalline deposit of shell-substance, which is very different in

structure and appearance from the porous shell wall of the segments.

The genus Calcarina is distinguished by a highly developed intermediate

skeleton with singular outgrowths, which is traversed by a system of

canals; through these the animal sends its pseudopodia into the water

for food to nourish the whole.

A homogeneous crystalline deposit invests almost the whole of the minute

spiral shell of a Calcarina, and sends out many cylindrical, but more

generally club-shaped spines in all directions, though they usually

affect more or less that of the equator, as in the typical form

Calcarina calcar, which is exactly like the rowel of a spur. The spines

are for the most part thick and clumsy, and give the shell a very

uncouth appearance, especially when their extremities are forked. The

turbinoid spire of the shell has a globose centre surrounded by about

five whorls progressively increasing in size, and divided by perforated

septa into chambers. Each whorl is merely applied to that preceding it,

and does not invest it in the least degree. Internally the turns of the

spire are separated from each other by the interposition of a solid

layer of shell-substance quite distinct from the walls of the chambers.

A crystalline deposit begins at the very centre of the spire in a thin

layer gradually increasing in thickness as it proceeds, and sending off

club-shaped spines from time to time so that the spines are of later and

later production, and become thicker and longer. From this it is evident

that the intermediate skeleton grows simultaneously with the turns of

the spire, but strange as it may seem, their growth is independent,

though both are nourished and increased by the sarcode in the interior

of the chambers. For the intermediate skeleton is traversed in every

part by an elongated network of canals, which begin from irregular

lacunæ or openings in the walls of the chambers, and extend to the

extremities of the spines. Through these canals threads of the sarcode

body of the animal within the chambers have access to the exterior, and

provide nourishment for the intermediate skeleton; while pseudopodia,

passing into the water through pores in the last partition of the shell,

provide for its growth and procure nourishment for the animal. The

communication between the adjacent chambers in the whorls, is by means

of a series of pores in the septa, or partitions; and it is through the

pores of the last septum that the pseudopodia of the animal have access

to the water to provide for the growth of the spire, for the punctures

on the surface are merely the terminations of some of the branching

canals. On approaching the surface the canals become crowded together in

some parts, leaving columns of the shelly skeleton unoccupied which

either appear as tubercles on the surface, or, if they do not rise so

high, form circular spots surrounded by punctations which are the

apertures of the canals.

The Rotaline series of the Globigerina family is one of the most

numerous and varied of the whole class of Foraminifera; but varied as

their forms are, they all bear the characteristic marks which

distinguish their order, with this essential difference, that in the

genus Globigerina each chamber of the spire has a communication with the

central vestibule by a crescent-shaped aperture, while in the Rotalinæ

each chamber only communicates by a crescentic aperture with that which

precedes and follows it.

In the Rotaline group the internal organization rises successively from

the simple porous partition between the chambers, to the double

partition with the radiating passages, and from the latter to the double

partitions, intermediate skeleton, and complicated system of canals. To

these changes the structure of the compound animal necessarily

corresponds, for it may be presumed that not only the chambers but all

the passages and canals in the interior of the shell are either

permanently or occasionally filled with its sarcode body.

However, it is in the Nummuline family that the Foraminifera attain the

highest organization of which they are capable. This family surpasses

all the Vitreous tribe in the density and toughness of the shell, the

fineness of its tubuli, and in the high organization of its canal

system. Their forms vary from that resembling a nautilus or ammonite to

a flat spiral or cyclical disk, like an Orbitolite, though vastly

superior to it in organization both with regard to the animal and to the

structure of the shell.

All the species of the genus Nummulite are spiral; in the typical form

the last turn of the spire not only completely embraces, but entirely

conceals, all that precede it. In general, the form is that of a double

convex lens of more or less thickness; some are flat, lenticular, and

thinned away to an acute edge, while others may be spheroidal with a

round, or obtuse edge. They owe their name to their resemblance to

coins, being, in general, nearly circular. Their diameters range from

1/16th of an inch to 4-1/2 inches, so that they are the giants of their

race; but the most common species vary from 1/2 an inch to 1 inch in

diameter.

[Illustration: Fig. 101. Section of Faujasina.]

Fig. 101 represents a section of the Nummulite Faujasina near and

parallel to the base of the shell. It shows a series of chambers

arranged in a flat spiral, and increasing in size from the centre to the

last turn of the spire, which embraces and conceals all that precede it.

Every segment of the animal is enclosed in a shell of its own, so that

they are separated from one another by a double wall and space between;

however, they are connected in the spiral direction by narrow passages

in the walls.

The segments of the animal in the exterior whorl have direct

communication with the water by means of a shelly marginal cord, _a_,

fig. 101, perforated by multitudes of minute tubes, less than the

1/10000 of an inch in diameter, through which threads of sarcode finer

than those of a spider’s web can be protruded. These tubuli are so very

fine and numerous, that they characterize the Nummuline family.

[Illustration: Fig. 102. Interior of the Operculina.]

Fig. 102 represents the interior of the Operculina, which is an existing

representation of the Nummuline type. Every segment of the animal is

enclosed in a shell of its own, but all the segments are connected in

the spiral direction by narrow passages in the walls as in the

Faujasina.

Although each of the interior whorls has its perforated marginal band,

the segments can have no direct access to the water; however, they are

indirectly brought into contact with it by means of a system of

branching shelly canals, radiating from the central chamber, ending in

conspicuous pores in the external surface of the shell. During this

course the canals send small tubes into the chambers on each side of

them; through these the internal segments of the animal can fill the

canals with cords of sarcode, and protrude them into the water, whence

they are supplied with food.

The genus Polystomella is distinguished by the high development of the

intermediate skeleton and the canal system that maintains it. The

Polystomella crispa (fig. 97, E), a beautiful species common on the

British coasts and in other temperate seas, has a lenticular form, the

1/16 to the 1/12 of an inch in diameter. It consists of a small number

of convolutions winding round the shorter axis of the lens, increasing

rather rapidly in breadth, and each one almost entirely enclosing its

predecessor, so that the shell is exactly alike on both sides, and only

the last convolution is to be seen. At the extremities of the axis there

is a mass of solid shell-substance, perforated by orifices which are the

apertures of a set of straight, parallel canals. In the figure only the

last convolution is visible, upon which the convex septal bands are very

conspicuous, dividing the surface into well marked segments, upon the

exterior edge of each of which there are strong transverse crenulations.

The only communication which the chambers have with the exterior, is by

means of a variable number of minute orifices near the inner margin of

the sagittate partition-plane, close to its junction with the preceding

convolution; a very high microscopic power is required to see them, as

well as the minute tubercles with which the surface of the shell is

crowded, more especially on the septal bands and in the rows of

depressions between the segmental divisions.

The sarcode animal itself corresponds exactly with the form and spiral

arrangement of the chambers so strongly marked on the exterior of the

shell. The segments form a spiral of crescents, smooth on the convex and

crenulated on the concave side; and from the latter threads of sarcode

proceed, which pass through pores in the inner margins of the

partitions, and unite them into one animal.

The Polystomella lives in tropical seas; P. crispa in temperate

latitudes, and P. striato-punctata inhabits the polar waters; the genus

is found everywhere.

Although variety of form without specific difference is characteristic

of the Foraminifera, it sometimes happens that identity of external form

is accompanied by an essential difference in internal structure. Of this

the Cycloclypeus is an instance; it is a rare species of nummuline,

dredged up from rather deep water off the coast of Borneo. The shell is

gigantic, some specimens being two and a half inches in diameter; but

its mode of growth is the same with that of the most complicated

Orbitolite. It consists of three superposed stages of circular discs,

each circle of chambers enclosing all those previously formed. However,

each segment of the animal being enclosed in its own shelly envelope, a

supplemental skeleton, and a radial, vertical and annular system of

canals, prove that the two animals belong to essentially different

families of Foraminifera. There are many instances, especially in the

Rotaline group, of isomorphism accompanied with generic difference; thus

no reliance can be placed on variety of external form, unaccompanied by

change of internal structure.

An attempt has been made in the preceding pages to describe a few

species most characteristic of some of the genera of this multitudinous

class; and of those selected a mere sketch of the most prominent

features of the animal and its abode is given, that some idea may be

formed of the wonderfully complicated structure of beings, which are

mostly microscopic specks. Yet the most minute circumstances in the

forms of the animals and their shells, with their varieties and

affinities, have been determined with an accuracy that does honour to

microscopic science.

They are now arranged in a natural system by William B. Carpenter, M.D.

F.R.S. assisted by William K. Parker, Esq., and T. Rupert Jones, Esq.,

and published in the Transactions of the Ray Society in 1862. To this

admirable work, the author is highly indebted.

It was known that different types of Foraminifera abound at different

depths on the coasts of the ocean; but it was long believed that no

living creature could exist in its dark and profound abyss. By deep-sea

sounding, it has been ascertained that the basin of the Atlantic Ocean

is a profound and vast hollow or trough, extending from pole to pole; in

the far south, it is of unknown depth, and the deepest part in the north

is supposed to be between the Bermudas and the Great Banks of

Newfoundland. But by a regular series of soundings made by the officers

of the navies of Great Britain and the United States, for the purpose of

laying a telegraphic cable, that great plain or steppe was discovered,

now so well known as the telegraphic plateau, which extends between Cape

Race in Newfoundland, and Cape Clear in Ireland. From depths of more

than 2,000 fathoms on this plateau, the ooze brought up by the sounding

machine consisted of 97 per cent. of Globigerinæ. The high state of

preservation of these delicate shells was no doubt owing to the perfect

tranquillity which prevails at great depths; for the telegraphic plateau

and the bed of the deep ocean everywhere is covered by a stratum of

water unruffled by the commotion raised by the hurricane which may be

raging on the surface. The greater number of the Globigerinæ were dead

empty shells; but although in many the animal matter was quite fresh,

Professor Bailly of New York could not believe that such delicate

creatures could live on that dark sea bed, under the pressure of a

column of water more than 2,000 fathoms high, a weight equal to rather

more than that of 340 atmospheres or 5,100 lbs. on every square inch of

sea-bed; wherefore he concluded that the tropical ocean and the Gulf

Stream, which absolutely swarm with animal life, must have been the

birth-place and home of these minute creatures, and that this mighty

‘ocean river,’ which divides at the Great Banks of Newfoundland, and

spreads its warm waters like a fan over the north Atlantic, deposits

their remains over its bed, which has thus been their grave-yard for

unknown periods, and which, in the lapse of geological time, may be

raised above the waves as dry land.

Professor Ehrenberg on the contrary concluded that residentiary life

exists at the bottom of the ocean, both from the freshness of the animal

matter found in the shells, and from the number of unknown forms which

are discovered from time to time at various and often great depths along

the coasts. This opinion has been confirmed beyond a doubt on several

occasions, especially by Dr. Wallich, who accompanied an expedition sent

under the command of Sir Leopold M‘Clintock, to sound the North Atlantic

for laying a telegraphic line.

In doing that two operations are requisite. The first is to ascertain

the depth: when that is known, the nature of the sea-bed must be

determined, and on that account a sample of it is then sounded for; but

owing to the difficulty of ascertaining the exact time at which the

ground is struck, a quantity of rope in excess of the depth is given

out, which lies on the bottom of the sea while the machine is being

drawn up, which occupies a considerable time when the depth is great.

About midway between Greenland and the north of Ireland, when the

machine was hauled up from a depth of a mile and a half, several

starfish were clinging with their long spiny arms to fifty fathoms of

the rope that had been lying on the surface of the sea-bed while the

machine was being drawn up, and to that part of the rope alone. They

continued to move their limbs energetically for more than a quarter of

an hour after they were out of the water. They certainly had not been

entangled in the line while swimming, because star-fishes are invariably

creeping animals. The deposit on which they had rested at the bottom of

the ocean contained ninety-five per cent. of Globigerinæ. Abundance of

these minute Foraminifera were found in the stomachs of the starfish;

which seemed to prove not only that the starfish were caught on their

natural feeding ground, but that their food was living organisms whose

normal abode is the surface of the bed of the deep ocean.

Dr. Wallich also discovered in the ooze brought up from a depth of

nearly two miles and a quarter a number of small bodies from 1/16 to 1/4

of an inch in length and about a line in breadth. They consisted of

equal globes arranged in a straight line like the Nodosaria, or built

up, each lying on part of the one below it, and increasing in size from

the uppermost about 1/1250 to the undermost about 1/450 of an inch in

diameter. Both of these forms, called coccospheres, consisted of sarcode

enclosed in a calcareous deposit; and were studded at nearly regular

distances by minute round or oval bodies concave below, and with an

aperture on their convex surface sometimes single, sometimes double.

These coccospheres were also found free in the ooze, and had been seen

previously by Capt. Dayman. They have likewise been seen as free

organisms living on the surface of the ocean.

The ooze in the bed of the Atlantic ocean, as well as of the

Mediterranean and Adriatic contains fifty per cent. of Globigerinæ; they

exist in the Red Sea, in the vicinity of the West Indian Islands, on

both sides of South America and near the Isle of France, but not in the

Coral Sea which is occupied by different genera. Though in utter

darkness, at the bottom of a deep ocean, these little creatures can

procure food by means of their pseudopodia, whose extreme sensibility

makes up for the want of sight; and the very excess of pressure under

which they live insures them a supply of oxygen at depths to which free

air cannot penetrate, for it is believed that the quantity of dissolved

air that water contains is in proportion to the pressure.

Fossil Foraminifera enter so abundantly into the sedimentary strata,

that Buffon declared ‘the very dust had been alive.’ 58,000 of these

fossil shells have been computed in a cubic inch of the stone of which

Paris and Lyons are built. The remains of these Rhizopods are for the

most part microscopic. M. D’Orbigny estimated that an ounce of sand from

the Antilles contained 1,800,000 shells of Foraminifera. A handful of

sand anywhere, dry sea-weeds, the dust shaken from a dry sponge, are

full of them.

When the finer portions of chalk amounting to one half or less are

washed away, the remaining sediment consists almost entirely of the

shells of Foraminifera, some perfect, others in various stages of

disintegration. In some of the hard limestones and marbles, the relics

of Foraminifera can be detected in polished sections and in thin slices

laid on glass. It is now universally admitted that some crystallized

limestones which are destitute of fossil remains, had been originally

formed by the agency of animal life, and subsequently altered by

metamorphic action; the opinion is gradually gaining ground among

geologists that such is the history of the oldest limestones.

At certain geological periods circumstances favoured the development of

an enormous multitude of individual animals. In the earlier part of the

Tertiary period the Nummulites acquired an extraordinary size. They were

like very large coins two or more inches in diameter, and were

accumulated in such quantities as to constitute the chief part of the

nummulitic limestone; a formation in some places 1,500 feet thick, which

extends through southern Europe, Libya, Egypt, Asia Minor, and is

continued through the Himalayan mountains into various parts of the

Indian peninsula, where it is extensively distributed. The Great Pyramid

of Egypt is built of this limestone, which gave rise to singular

speculations with regard to the Nummulites in very ancient and even in

more recent times. Although this is incomparably the greatest, it is by

no means the only instance of an accumulation of the fossil shells of

individual animals. The ‘Lingula flags,’ a stratum in the upper Cambrian

series of North Wales, was so named from the abundance of the Brachiopod

Lingula that it contains.

Professor Ehrenberg discovered that the shells of the Foraminifera

sometimes undergo an infiltration of silicate of iron, which fills not

only the chambers, but also their canal-system even to its minutest

ramifications, so that if the shell be destroyed by dilute acid, a

perfect cast of the sarcode matter remains. The greensands in the

different geological strata from the Silurian formation upwards, are

chiefly composed of these casts; and Professor Baily of the United

States more recently discovered that a process of infiltration is even

now taking place in some parts of the ocean bed, and that beautiful

casts of Foraminifera may be obtained by dissolving their shells with

dilute acid.

A most extensive comparison of the Foraminiferous group of Rhizopods,

recent and fossil, has been made by Messrs. Parker and Rupert Jones from

almost every latitude on the globe, from the arctic and tropical seas,

from the temperate zones in both hemispheres, and from shallow as well

as deep-sea beds. They have also reviewed the fossil Foraminifera in

their manifold aspects as presented by the ancient geological faunas

throughout the whole series from the Tertiary down to the Carboniferous

strata inclusive; and have come to the astonishing conclusion that

scarcely any of the species of the Foraminifera met with in the

secondary rocks have become extinct. All that they had seen have their

counterparts in the recent Mediterranean deposits. Throughout that long

series of geological epochs even to the present day, the Foraminifera

show no tendency to rise to a higher type; but variety of form in the

same species prevailed then as it does now.

Subsequently to this investigation, a gigantic Orbitulite twelve inches

in diameter, and the third of an inch thick, has been found in the

Silurian strata in Canada. The largest recent species Dr. Carpenter had

seen was about the size and thickness of a shilling.

The lowest stratum of the Cambrian formations has been regarded as the

most ancient of the Palæozoic rocks; now, however, strata of

crystallized limestone near the base of the Laurentian system, which is

50,000 feet thick in Canada, are discovered by Sir W. E. Logan to have

been the work of the Eozoön Canadense, a gigantic Foraminifer, at a

period so inconceivably remote that it may be regarded as the first

appearance of animal life upon the earth. In a paper published by Dr.

Carpenter, in May 1865, he expressed his opinion that the Eozoön would

be found in the older rocks of central Europe; and in the December

following he received specimens from the fundamental quartz rocks of

Germany, in which he found undoubted traces of the Eozoön. Here the

superincumbent strata are 90,000 feet thick; the transcendent antiquity

of the Eozoön is therefore beyond all estimation.

The fossil Eozoön consists of a succession of parallel rows or tiers of

chambers, in which the sarcode of the living animal had been replaced by

a siliceous infiltration, so that when the calcareous shell was

destroyed by dilute acid, the cast was found to be precisely like that

of a Nummulite; thin slices of it taken in different directions being

examined with a microscope, it was found that the siliceous matter had

not only filled that portion of the chambers which had been occupied by

the sarcode-body of the animal and the canal-system, but had actually

taken the place of the pseudopodial threads, the softest and most

transitory of living substances, which were put forth through tubuli in

the shell-walls of less than the 1/10000 part of an inch in diameter.

‘These are the very threads themselves turned into stone by the

substitution which took place, particle by particle, between the sarcode

body of the animal and certain constituents of the water of the ocean,

before the destruction of the sarcode by ordinary decomposition.’[9] The

shell had an intermediate skeleton, but the minute tubes in the walls of

the chambers are so characteristic of the Nummulites, that they were

sufficient alone to determine the relationship of the Eozoön to its

modern representative.

The external shape and limits to the size of the individual Eozoön have

not been determined with certainty, on account of its indefinite mode of

growth, and the manner in which the fossilized masses are connected with

the highly crystalline matrix in which they are imbedded; there is no

doubt, however, that they spread over an area of a foot or even more,

and attained a thickness of several inches. As they seem to have

increased laterally by buds which never fell off, they formed extensive

reefs; at the same time they had a vertical growth, for in some of the

reefs the older portions appear to have been fossilized before the newer

were built up on them as a base, exactly like the coral reefs in the

tropical ocean of the present day,[10] with this difference however,

that shells and other crustaceans are associated with the corals, while

no organic body has been found in the Eozoön reefs; nevertheless the

Eozoön must have had food. It may therefore be inferred that parts at

least of that primeval ocean swarmed with animal life, whose remains

have been obliterated by metamorphic action. Carbon (which in the form

of graphite both constitutes distinct beds, and is disseminated through

the siliceous and calcareous strata of the Laurentian series, as well in

Norway as in Canada), may indicate the existence of vegetation in the

Eozoön period.

The Eozoön is by no means confined to Canada and central Europe. The

serpentine marble of Tyree which forms part of the Laurentian system on

the west of Scotland, and a similar rock in Skye, when subjected to

minute examination, are found to present a structure clearly identical

with that of the Canadian Eozoön. And the like structure has been

discovered by Mr. Sanford in the serpentine marble of Connemara, known

as Irish green. The age of that rock however, is doubtful: for when it

was discovered to contain Eozoön, Sir Roderick Murchison who had

previously studied its relations was at first inclined to believe it

belonged to the Laurentian series; now however, he considers the

Connemara marble to be of the Silurian age. ‘If this be the case it

proves that the Eozoön was not confined to the Laurentian period, but

that it had a vast range in time, as well as in geographical

distribution; in this respect corresponding to many later forms of

Foraminifera which have been shown by Messrs. Parker and Rupert Jones to

range from the Trias to the present epoch.’[11]

The Carpenteria found in the Indian seas forms a link between the

Foraminifera and Sponges. The shell is a minute cone adhering to the

surface of corals and shells, by its wide base which spreads in broad

lobes. Double-walled chambers and canals form a spiral within it, and

are filled with a spongy sarcode of a more consistent texture than the

sarcode of the Foraminifera, which in the larger chambers is supported

by siliceous spicules similar to those which form the skeletons in

sponges.

CLASS III.—SPONGES.

According to the observations of Mr. Carter, sponges begin their lives

as solitary Amœbæ which grow by multiplication into masses, and assume

endless forms according to the species; turbinate, bell-shaped, like a

vase, a crater, a fan, flat, foliaceous and lobed or branching and

incrusting the surface of stones. All the Amœbæ are so connected as to

form one compound animal. The whole substance of a sponge is permeated

by innumerable tubes which begin in small pores on the surface, and

continually unite with one another as they proceed in their devious

course to form a system of canals increasing in diameter and ending in

wide openings called oscula, on the opposite side of the mass. Currents

of water enter through the pores on the surface, and bring minute

portions of food which are seized upon by a vast multitude of Amœbæ with

long cilia which form the walls of the tubes and canals; and after they

have extracted the nutritious part, the offal is carried into the sea

through the oscula, by the current of water whose flux is maintained by

the vibrations of the cilia. In the compressed and many of the tubular

sponges the water passes through them in a straight line; in branched

and encrusting sponges, the afferent and efferent openings are on the

same surface. The water is inhaled continuously and gently like an

animal breathing, but it is rapidly and forcibly ejected; and in its

passage it no doubt furnishes oxygen to aërate the juices of the

compound animal, whose flesh or sarcode is irritable while alive, and

which has the power to open and shut the pores and oscula of the canals,

for the whole sponge forms one compound creature whose mass is nourished

by the myriads of Amœbæ of which it is constituted.

Within the animated sarcode mass of the sponges there is in most cases a

complicated skeleton of fibrous network, either horny, calcareous, or

siliceous, which supports the soft mass, and determines its form.

Besides the skeleton, the mass of sponges is for the most part

strengthened and defended by siliceous, and more rarely by calcareous,

spines or spicules, either imbedded among the fibres of the skeleton, or

fixed to them by their bases. The fibres of the skeleton network always

unite, whether they be horny, calcareous, or siliceous; the spicules

never, though they often lie in confused heaps over one another. They

are of innumerable forms and arrangements. Some are like long needles

lying close together in bundles, pointed or with a head like a pin at

one or both ends; a great number are stellate with long or short rays;

there may even be several different forms in the same sponge. Many

calcareous sponges have cavities full of organic matter; and when the

calcareous matter is dissolved by dilute acid, the organic base is left.

The common commercial sponges have a skeleton which consists of a

network of tubular, horny, tough, and elastic fibres which cross in

every direction. They have no spicules or very few; and when such do

project from the horny skeleton, they are generally conical, attached by

their bases, and their surface is often beset with little spines

arranged at regular intervals, which gives them a jointed appearance.

The common sponge which is so abundant in the Mediterranean has many

forms; those from the coast of North America are no less varied, but

that most used in the United States is turbinate, concave, soft, and

tomentose.

[Illustration: Fig. 103. Section of Sponge.]

In the calcareous sponges a mass of three-rayed spicules surround the

interior canals, where they are held together by a cartilaginous

substance which is wanting in the horny sponges, but which remains in

this order after the destruction of the more delicate matter when the

sponge is dried.[12] The pores are also occasionally defended by the

projecting points of half buried spines.

In nearly every species of this order the pores on the surface are

protected by spicules; and they are also projected from the surface of

the large cloacal cavity, and curved towards its opening, to defend it

from Annelids and other enemies.[13] Some species have a long ciliary

fringe at the orifice of the cavity, through which the water may pass

out, but no animal can come in.

The spicula and skeleton of most of the marine sponges are siliceous and

singularly beautiful; the skeleton of the Dactylocalyx pumiceus of

Barbadoes is transparent as spun glass; and a species from Madagascar

has numerous simple transparent and articulated spicules implanted in

the siliceous fibres of the skeleton. The Cristata, Papillaris, Ovulata,

and many more have siliceous skeletons, some garnished with spicules of

various forms, and the surface occasionally covered with a layer of

siliceous granules.

The variety in the size, structure, and habits of the marine sponges is

very great: temperate and tropical seas have their own peculiar genera

and species; some inhabit deep water, others live near the surface,

while many fix themselves to rocks, sea-weeds, and shells, between high

and low water mark. There are very few dead oyster, whelk, scallop, and

other shells that escape from the ravages of the Cliona, an extremely

minute burrowing sponge of the simplest structure, which has a coat of

siliceous spicules supposed to be the tools with which it tunnels a

labyrinth through the mid-layer of the shell, in a pattern that varies

with the species of the sponge. A communication is formed here and there

with the exterior by little round holes, through which the sponge

protrudes its yellow papillæ. From the force exhibited by this little

sponge, it may perhaps be inferred to possess a rudimentary muscle and

nerve.[14]

Sponges are propagated twice in the year by minute ciliated globules of

sarcode, detached from the interior of the aquiferous canals, which swim

like zoospores to a distance, come to rest, and lay the foundation of

new sponges. The little yellow eggs of Halichondria panicea are lodged

in the interstices between the interior canals; when mature, they are

oval and covered with cilia, and are carried out by the currents; and

after swimming about for some days fix on a solid object, become covered

with bristles, spread out into a transparent film, charged with

contractile vesicles of different sizes in all degrees of dilatation and

contraction, as well as with sponge ovules. Spicules are developed at

the same time, and these films ultimately become young sponges, and if

two happen to meet they unite and are soldered together.[15] Besides

eggs, larger bodies covered with radiating spicules are produced,

containing granular particles of sarcode, each of which when set free by

the rupture of the envelope, becomes an Amœba-like creature, and

ultimately a sponge.

Fresh-water sponges are sometimes branched, and sometimes spread over

stones, wood, and other substances; and one species covers an earthy

mass some inches thick formed by its own decayed matter. The skeleton of

such species as have one, consists of bundles of siliceous spicules,

held together and mixed with groups of needles, the rods of which

project through the surface of the sponge and render it spinous. The

motions in the gelatinous sarcode mass are the most remarkable feature

in the fresh-water sponges, which all belong to the genus Spongilla. Mr.

Carter observed that portions of the surface of some individuals of the

Spongilla fluviatilis in his aquarium had long cilia by means of which

they rapidly changed their places during the spring, but when winter

came they emitted processes from such parts of their surfaces as were

free from cilia and retracted them again just like Amœbæ. These portions

often had cells, and when the Amœba-like motions ceased, a nucleus and

nucleolus appeared within them, and at last the whole gelatinous sarcode

mass consisted of these cells or globules. Some had no nucleus, but were

filled with green or colourless granules.

At certain seasons of the year, whatever the form of the fresh-water

sponges may be, a multitude of minute hard yellow bodies are produced in

their deeper parts. They consist of a tough coat containing radiating

spicules like a pair of spoked wheels united by an axle with a pore in

its surface. Within this last there is a mass of motionless granular

cells, and when put into water the cells come out at the pore and give

rise to new sponges.

Insulated groups of germs covered with cells called swarm-cells seem to

form parts of the sponges; they lie completely within the mass of the

living sponge. They have the form of a hen’s egg, are visible to the

naked eye, and when they come into the water they swim in all directions

for a day or two; become fixed; a white spot within is enlarged; and the

constituents of young sponges appear.[16]

The generic forms of fossil sponges augment in number and variety from

the Silurian to the Cretaceous beds, where the increase is rapid; but

all the sponges which had a stony reticulated form without spicules

passed away with the Secondary epoch, so that the family has no

representatives in the Tertiary deposits or existing seas. The

calcareous sponges which abound in the Oolite and Cretaceous strata, and

attain their maximum in the Chalk, are now almost extinct, or are

represented by other families with calcareous spicules. Siliceous fossil

sponges are particularly plentiful. In England extensive beds of them

occur in the Upper Greensand, and in some of the Oolitic and

Carboniferous Limestones; and some beds of the Kentish Rag are so full

of their siliceous spicules, that they irritate the hands of the men who

quarry them. Since every geological formation except the Muschelkalk is

found in England, the number and variety of fossil sponges are very

considerable. The horny sponges are more abundant now than they were in

the former seas. According to M. D’Orbigny the whole number of fossil

sponges known and described amount to thirty-six genera and 427 species,

which is probably much below the real number.[17]

CLASS IV.—INFUSORIA.

The Infusoria, which form the second group of the Protozoa, are

microscopic animals of a higher grade than any of the preceding

creatures, although they go through their whole lives as isolated single

cells of innumerable forms. They invariably appear in stagnant pools and

infusions of animal and vegetable matter when in a state of rapid

decomposition. Every drop of the green matter that mantles the surface

of pools in summer teems with the most minute and varied forms of animal

life. The species called Monas corpusculus by the distinguished

Professor Ehrenberg, has been estimated to be 1/2000 part of a line in

diameter. ‘Of such infusoria a single drop of water may contain

500,000,000 of individuals, a number equalling that of the whole human

species now existing upon the face of the earth. But the varieties in

size of these animalcules invisible to the naked eye are not less than

that which prevails in almost any other natural class of animals. From

the Monad to the Loxades or Amphileptus, which are the fourth and sixth

part of a line in diameter, the difference in size is greater than

between a mouse and an elephant; within such narrow bounds might our

ideas of the range in animal life be limited if the sphere of our

observation was not augmented by artificial aid.’[18]

This singular race of beings has given rise to the erroneous hypothesis

of equivocal or spontaneous generation, that is to say, the production

of living animalcules by a chemical or even fortuitous combination of

the elements of inert matter. That question has been decided by direct

experiment, for Professor Schultz kept boiled infusions of animal and

vegetable matter for weeks in air which had passed through a red-hot

tube, and no animalcules were formed, but they appeared in a few hours

when the same infusions were freely exposed to the atmosphere, which

shows clearly that the germs of the lowest grade of animal life float in

the air, waiting as spores do, till they find a nidus fit for their

development.

M. Pasteur, Director of the Normal School in Paris, in a series of

lectures published in the ‘Comptes Rendus,’ has not only proved that the

atmosphere abounds in the spores of cryptogamic fungi and moulds, but

with infusoria of the form of globular monads, the Bacteria, and

vibrios, which are like little rods round at their extremities and

extremely active. The Bacteria mona and especially the Bacteria terma,

are exceedingly numerous. These minute beings are the principal agents

in the decomposition of organic matter. They are more numerous in dry

than in wet weather, in towns than in the country, on plains than on

mountains.

In a memoir read at the Academy of Sciences, Paris, Mr. J. Samuelson

mentions that he had received rags from Alexandria, Japan, Melbourne,

Tunis, Trieste and Peru. He sifted dust from the rags from each of these

localities respectively through fine muslin into vases of distilled

water. Life was most abundant in the vases containing dust from Egypt,

Japan, Melbourne, and Trieste. The development of the different forms

was very rapid, and consisted of protophytes, Rhizopods and true

Infusoriæ. In most of the vases monads and vibrios appeared first, and

from these Mr. Samuelson traced a change first into one then into

another species of infusoria. In the dust from Japan he followed the

development of a monad into what appeared to be a minute Paramœcium,

then into Lexodes cucullus, and finally into Colpoda cucullus. From

these and other experiments it is proved that many infusoria now classed

as distinct types are really one and the same animal in different states

of development. That appears to be the case also with the Amœbæ. In the

dust from Egypt Mr. Samuelson found a new Amœba whose motions were very

rapid; as to shape and mode of motion he compared it to soap bubbles

blown with a pipe. He traced the gradual changes of the globular form of

this Amœba until its pseudopodia were in full action, its increase by

conjugation, and other circumstances of its life. In the same dust and

in that only, the development of the Protococcus viridis was seen, and

that in such abundance that at last the water was tinged green by that

plant. In the dust from Egypt a vibrio was changed into a vermiform

segmented infusoria of an entirely new type. Its length varied from the

1/150 to 1/100 of an inch, each ring was ciliated, and the whole series

of cilia extending along the body acted in concert; a circlet of them

surrounded the anterior segment; a canal seemed to extend throughout the

body. It was propagated by bisection; the two parts remained attached to

one another; an independent ciliary motion was observed in each which

did not interfere with the motion of the whole. It was supposed to be a

larval form or series of forms. Mr. Samuelson’s observations show, that

the atmosphere in all the great divisions of the globe is charged with

representatives of the three kingdoms of nature, animal, vegetable, and

mineral: that the animal germs not only include the obscure types of

monads, vibrios, and Bacteria, but also the Glaucoma, Cyclides,

Vorticella, and other superior Infusoriæ, and occasionally though very

rarely germs of the Nematode worms.

It has been already mentioned that many of the microscopic fungi are

ferments, aiding greatly in the decomposition of organic matter. They

however are by no means the only agents in decomposition. The moment

life is extinct in an animal or vegetable, Infusoria of the lowest grade

seize upon the inanimate substance, speedily release its atoms from

their organic bond, and restore them to the inorganic world whence they

came. The ferment which transforms lactic acid into butyric acid is a

species of vibrio which abounds in the liquid, isolated or united in

chains; they glide, pirouette, undulate, and float in all directions,

and multiply by spontaneous division. Vibrios possess the unprecedented

property of living and propagating without an atom of free oxygen; they

not only live without air, but air kills them. This singular property

forms an essential difference between the Vibrios and the Mycoderms: the

former cannot live in oxygen; the latter cannot live without it, and as

soon as it is exhausted within the infusion, they go to the surface to

borrow it from the atmosphere.

There are also two groups of Infusoria which possess these opposite

characters, one being unable to live in oxygen, while the other cannot

live without it; sometimes they even inhabit the same liquid. When the

tartrate of lime is put into water along with some ammoniacal and

alkaline phosphates, a Monad, the Bacteria terma, and other Infusoria

appear after a time. These little animals bud rapidly in an infusion of

animal matter, then a slight motion is produced by the appearance of the

Monas corpusculum and the Bacterium terma, which glide in wavy lines in

all directions in quest of the oxygen dissolved in the liquid, and as

soon as it is exhausted they go to the surface in such numbers as to

form a pellicle, where by aid of the oxygen they form the simple binary

compounds water, ammonia, and carbonic acid. In the meantime the

Vibrios, which are without oxygen, are developed below, and keep up the

fermentation, and between the two, the work of decomposition is

completed.

It is not the worm that destroys our dead bodies; it is the Infusoria,

the least of living beings. The intestinal canal of the higher animals,

and of man, is always filled during life not only with the germs of

vibrios, but with adult and well-grown vibrios themselves. M.

Leewenhoeck had already discovered them in man, a fact which has since

been confirmed. They are inoffensive as long as life is an obstacle to

their development, but after death their activity soon begins. Deprived

of air and bathed in nourishing liquid, they decompose and destroy all

the surrounding substances as they advance towards the surface. During

this time, the little Infusoria, whose germs from the air had been

lodged in the wrinkles and pores of the skin, are developed, and work

their way from without inwards, till they meet the vibrios, and after

having devoured them, they perish, or are eaten by maggots.

Of all the Infusoria and ferments the Vibrios are the most tenacious of

life; their germs resist the destructive effect of a temperature of 100°

Cent. The spores of the Mucedines are still more vivacious; they grow

after being exposed to a heat of 120° Cent., and are only killed by a

temperature of 130° Cent. As neither spores of the fungi nor the germs

of the Infusoria are ever exposed to so high a temperature while in the

atmosphere, they are ready to germinate as soon as they meet with a

substance that suits them.

M. Ehrenberg has estimated that the Monas corpusculum is not more than

the 1/24,000th part of an inch in diameter; whence Dr. M. C. White,

assuming that the ova of the Infusoria and the spores of minute fungi

are only the 1/10th part in linear dimensions of their parent organisms,

concludes that there must be an incalculable amount of germs no larger

than the 1/240,000th or 1/100,000th part of an inch in diameter; and

since according to MM. Sullivant and Wormley, vision with the most

powerful microscope is limited to objects of about the 1/80,000th part

of an inch in diameter, we need not be surprised if Infusoria and other

organisms appear in putrescible liquids in far greater numbers than the

germs in atmospheric dust visible by the aid of microscopes would lead

us to expect.

The ferments are the least in size and lowest in organization of all the

Infusoria. The higher group which abounds in stagnant pools and ditches

are exceedingly numerous, and their forms are varied beyond description.

They are globular, ovoid, long and slender, short and thick, many have

tails, one species is exactly like a swan with a long bending neck, but

whatever the form may be, all have a mouth and gullet. Although the skin

of the Infusoria is generally a mere pellicle, that of the red

Paramœcium and some others resembles the cellulose covering of a

vegetable cell, engraved with a pattern; but in all cases respiration is

performed through the skin.

Whatever form the cell which constitutes the body of the Infusoria may

have, the highly contractile diaphanous pellicle on its exterior is

drawn out into minute slender cilia which are the locomotive organs of

these creatures. Vibrating cilia form a circlet round the mouth of some

of these animalcules, a group of very long ones are placed like whiskers

on each side of it, as in the Paramœcium caudatum, and in some cases

there is a bunch of bristles in front. Certain Infusoria have cilia in

longitudinal rows, and in many the whole body is either partially or

entirely covered with short ones. In some Infusoria their vibrations are

constant, in others interrupted, and so rapid that the cilia are

invisible. These delicate fibres which vary from the 1/500th to the

1/13,000th part of an inch in length, move simultaneously or

consecutively in the same direction and back again, as when a fitful

breeze passes over a field of corn. These animalcules seize their prey

with their cilia, and swim in the infusions or stagnant pools, in which

they abound, in the most varied and fantastic manner; darting like an

arrow in a straight line, making curious leaps and gyrations, or fixing

themselves to an object by one of their cilia and spinning round it with

great velocity, while some only creep. These motions, which bring the

animalcules into fresh portions of the liquid, are probably excited by

the desire for food and respiration.

[Illustration: Fig. 104. Paramœcium caudatum. _a_ _a_, contractile

vesicles; _b_, mouth.]

[Illustration: Fig. 105. Kerona silurus.—_a_, contractile vesicle; _b_,

mouth; _c_ _c_, animalcules which have been swallowed by the Kerona.]

None of the Infusoria have regular jointed limbs, but certain families

of the higher genera have peculiar and powerful organs of locomotion

partly consisting of strong ciliary bristles placed on the anterior in

rows, used for crawling or climbing, and partly consisting of groups of

strong processes which serve as traction feet, generally trailing behind

the animal while swimming, or used to push it forward. When the bristles

or cilia of this high group of Infusoria are used for crawling their

motions may be traced to the contraction of the skin; but in the

Infusoria that are never fatigued though their cilia vibrate incessantly

night and day, it may be presumed that these motions are altogether

independent of the will of the animal, in as much as there are

innumerable cilia in the human frame that are never at rest during the

whole course of our existence, nor do their vibrations cease till a

considerable time after death—a striking instance of unconscious and

involuntary motion.

The cell which constitutes the body of the Infusoria is filled with

sarcode, which is the receptacle of the food, and in that substance all

the internal organs of the animalcule are imbedded. In the higher genera

it is full of granular particles of different sizes and forms, and it

contains a nucleus in its centre, characteristic of cellular protozoa

generally. The nucleus is of a dull yellow colour, and is enclosed in a

transparent capsule, which in the smaller Infusoria reflects light

brilliantly. It is generally of an ovoid form and single, but in several

species the nucleus is double, and in others there are several nuclei.

The Infusoria have a distinct mouth and gullet, and for the most part

another aperture for ejecting the indigestible part of their food,

though some discharge it by the mouth, others through any part of their

surface. A few of the larger Infusoria devour the smaller; others feed

on minute vegetable particles, chiefly diatoms. Solid substances that

are swallowed are collected into little masses mixed with water, and

enter into clear spherical spaces called vacuoles in various parts of

the sarcode, where they are partially digested. When the animal has not

had food for some time, clear spaces only filled with a very transparent

fluid are seen, variable both in size and number. It was on account of

the digestive vacuoles that the Infusoria were called Polygastria by

Ehrenberg.

Transparent contractile vesicles of a totally different nature from the

vacuoles are peculiarly characteristic of such Infusoria as have a

digestive cavity. They exist either singly or in even numbers, from 2 to

16, according to the species, and never change their places; but they

dilate and contract rhythmically at pretty regular intervals. When

dilated, they are filled with a clear, colourless fluid, the product of

the digestive process which they are supposed to diffuse through the

body of the animal.

The Euglena, a very extensive genus of Infusoria, have smooth bodies and

green particles imbedded in the sarcode, which fills their interior; and

M. Wöhler discovered that the green mantle covering the saline springs

at Rodenberg and Königsborner, which consists of three species of these

green Infusoria, gives out bubbles of pure oxygen; thus indicating a

respiratory process in these animals, the same with that in plants,

namely, fixing the carbonic acid of the atmosphere and exhaling oxygen,

a singularly close analogy, if not identity, of action. The Euglenæ are

also distinguished by an irregular oblong space in the head filled with

a red liquid; but, as it does not contain a crystalline lens, it can

only be regarded as the very earliest rudiment of an eye, totally

incapable of distinguishing objects, though probably sensible to the

influence of light. They swim with a smooth gliding and often rotatory

motion, producing a kind of flickering on the surface of the water by

the lashing of a long filament attached in front, and supposed to be

their only organ of locomotion; nevertheless, Mr. Gosse thinks that they

are covered with most minute cilia from their manner of swimming. The

Euglena acus is one of the prettiest of these little animals; it is long

and slender, of a sparkling green with colourless extremities, a

thread-like proboscis, and a rich crimson spot. When it swims it

rotates, and a series of clear, oblong bodies are seen towards the head,

and another at the tail, as if they were imbedded in the flesh round a

hollow.

The Loxades bursaria, which is a giant among its fellows, has an ovoid

body with green particles imbedded in its interior. The outer skin is

spirally grooved, so as to form a kind of network, the elevated points

of which support the cilia with which its body is beset. It has a mouth

and gullet lined with cilia, which force the food in balls into the soft

matter in the interior, where both the food and the green particles

circulate, being carried along by a gyration of the gelatinous matter in

which they are imbedded.

A species of Peridinium, which is luminous at night, and occasionally

covers large portions of the Bay of Bengal with a scarlet coat by day,

nearly approaches the character of the unicellular Algæ. Mr. J. H.

Carter observed that at first, when these animalcules were in a state of

transition, their nearly circular bodies were filled with translucent

green matter, closely allied, if not identical with, chlorophyll, which

disappeared when the animal approaches its fixed state, and a bright red

took its place: the Infusoria were then visible to the naked eye, and

the sea became scarlet. The scarlet state only lasts for a few days, for

each of these innumerable Infusoria becomes encysted or capsuled, and

either floats on the water, or sinks to the bottom and remains

motionless. The Euglena sanguinea has a scarlet state analogous to that

of the Peridium. It is so minute and versatile that it is difficult to

ascertain its true form, which, however, seems to be a spindle shape,

with a pointed and blunt round head. In general it is of a rich emerald

green, with perfectly clear, colourless extremities; but it sometimes

occurs of a deep red, and in such multitudes as to give the water the

appearance of blood.[19]

[Illustration: Fig. 106. Noctiluca.]

The Noctiluca miliaris, a luminous inhabitant of the ocean, and the most

beautiful of the Infusoria, is distinguished by its comparatively

gigantic size, and by its brilliant light, which makes the sea shine

like streams of silver in the wake of a ship in a warm summer evening,

when they come to the surface in countless multitudes. It is a globular

animal like a minute soap bubble, consisting of gelatinous matter, with

a firmer exterior, and being about the thirtieth of an inch in diameter,

it is visible to the naked eye, when a glass in which it is swimming is

held to the light. On one side of the globe there is an indentation,

from whence a tail of muscular fibre springs striped with transverse

rings, which aids the animal in swimming. At the root of the tail lies

the mouth, bordered on one side by a hard dentile lip leading into a

funnel-shaped throat, from whence a long flickering cilium is protruded,

supposed to be connected with respiration. The throat leads into a large

cavity in the gelatinous substance, from whence the rudiments of an

alimentary canal descend. From the internal surface of the globe sarcode

fibres extend through the gelatinous matter, so as to divide it into a

number of irregular compartments, in which vacuoles are often seen. They

give buoyancy to the animal, and enable it to rise and sink in the

water, but seem to disappear when the food is digested. The sarcode

fibres constantly change their form and position, and the electric light

emitted by a direct exertion of nerve power, which seems to be constant

to the naked eye, really consists of momentary scintillations that

increase in rapidity and intensity by the dash of an oar or the motion

of the waves.

The Noctiluca is propagated by spontaneous division, a line appears

bisecting the globe, which becomes more and more constricted till the

animal is like a dumb-bell; the slender thread separating the two parts

is then broken by their efforts to get free; the two new creatures swim

off in different directions, and soon assume their adult form. But in

many individuals there are clear, yellow globules with a well-defined

nucleus, of a rich reddish-brown, which are the germs of the animal.

Most of the Infusoria multiply by continuous bisection, like the

unicellular Algæ. The division generally begins with the nucleus, and is

longitudinal or across, according to the form and nature of the animal,

and is accomplished with such rapidity, that, by the computation of

Professor Ehrenberg, 268,000,000 of individuals might be produced from

one single animalcule of the species Paramœcium in a month. The

Paramœcia are reproduced too by gemmation, and, as they are male and

female, they are reproduced also like the higher classes.

The Infusoria have another mode of increasing. The animalcules either

draw in or lose their cilia, and consequently come to rest. The animal

then assumes a more globular form, and secretes a gelatinous substance

from its surface, which hardens into a case or cyst, in which its body

lies unattached and breaks up into minute ciliated gemmules, which swim

forth like zoospores as soon as they come into the water by the thinning

away of part of the cyst. In fact the animal is resolved into its

offspring, which, as soon as free, gradually acquire the parent’s form,

though at first they may bear no resemblance to it. The scarlet Peridium

seen by Mr. Carter in the Bay of Bengal is propagated in this manner.

For the parent Peridium is broken up within its cyst into from two to

four new ones, each of which when set free and grown up might undergo

the same process.

The Loxades bursaria increases by three distinct methods, and sometimes

by two at a time. In autumn, or the beginning of winter, six or eight

germs containing granular matter and one or more hyaline nuclei are

formed within the animal, each enclosed in two contractile cysts: they

lie freely in the cavity of the body, and come one by one into the water

through a canal ending in a protuberance in the skin. During this time

the pulsations of the vesicles within the Loxades are continued, but the

gyration of the green particles is suspended till all the germs are

excluded and swim away, and then it is renewed as vigorously as ever. At

first the young are totally unlike their parent, but by degrees acquire

its form. The Loxades is also increased by division, sometimes across,

sometimes longitudinally, and, in the latter case, one half is

occasionally seen to contain germs which have been excluded before the

other half had separated, so that the two distinct systems of

propagation are simultaneous.[20]

The Vorticella nebulifera and some others of the Infusoria are

remarkable for the diversity of their reproductive powers; for, besides

division and gemmation, they are reproduced by a kind of alternate

generation, accompanied by singular metamorphoses. The Vorticella, one

of the most beautiful animals of its class, lives in pools of fresh

water: groups of them are found on almost every mass of duckweed like

little blue bells upon slender stalks, creating active currents in the

water by the vibrations of long and powerful cilia with which the margin

of the bell is fringed. The lip or edge of the bell is bent outwards

into a permanent rim, and a deep groove cleaves the rim on one side, in

which a wide cavity forming the mouth is placed. The mouth, the short

throat or gullet, and the whole bell, are bristled with vibratile cilia.

[Illustration: Fig. 107. Vorticellæ.]

The Vorticellæ feed on vegetable organisms, chiefly diatoms, and are

exceedingly voracious. The cilia round the rim of the bell entangle the

food, draw it into the mouth, and those in the gullet force particle

after particle mixed with water into vacuoles which they make in the

interior of the soft sarcode which fills the bell, and there the

particles undergo rotation till digested and absorbed, and, if refuse

remain, it is ejected through a softer part in the outer layer of the

bell.

[Illustration: Fig. 108. Acineta.]

The stem that fixes the animal to a solid object is a tubular

continuation of its outer membrane, containing a highly contractile

filament; and, as the creature is extremely sensitive to external

impressions, it folds up the ciliated rim of its bell, and its stalk

shrinks down in a spiral on the slightest alarm, but the bell opens and

the stalk stretches out again as soon as the alarm is over. When a

Vorticella is reproduced by division, the bell separates longitudinally

into two parts; one is often smaller than the other, and separates from

its parent, swims about till it gets a stem, and fixes itself to an

object. When the two parts are of equal size, the division extends to a

greater or less distance down the stalk, and as each of these become

perfect bells, and do not fall off but subdivide in the same manner, it

follows that, by successive divisions, a whole group of these beautiful

animals may spring from the same stem, as in fig. 107.

The Vorticella has a most wonderful mode of reproduction common to a few

other Infusoria. A gelatinous substance is secreted by the bell, which

hardens and envelopes it in a cyst; the encysted bell then separates

from its stalk, and is transformed into an infusorial animal called an

Acineta (fig. 108), closely resembling the Actinophrys sol with

radiating filaments which it continually stretches out and draws in. A

motile ciliated embryo, or Vorticella bud, is then formed within the

Acineta, which, after a time, comes out at a slit in its side, swims

about, gets a stem, fixes to some object, and is developed into a

Vorticella. The slit closes again, and the Acineta keeps moving its

filaments as usual, and another motile embryo is formed within it, which

is emitted by a slit in the same manner, and is also developed into a

Vorticella. As these young Vorticellæ, or bell animals, may undergo the

same transformations, there may be an indefinite alternation of the two

forms. The Vorticella-bud, when it issues from the slit in the Acineta,

has an oval form, with a circlet of long cilia at its narrow end, a

mouth at the more obtuse, a nucleus, and contractile vesicles, and,

after swimming about till it finds a suitable place, it becomes fixed by

one end of its oval body, a style or stem is formed, which rises

rapidly, and the adult shape is developed. The Acinetæ are said to live

upon Infusoria: they apply the dilated apex of their rays as sucking

discs to the animal, and suck its contents till it dies. The Tricoda

linceus undergoes metamorphoses analogous to those of the Vorticella,

but more numerous and complicated.[21]

Most of the Vorticellæ, and probably the majority of Infusoria, remain

unchanged for a time within their cysts, being then in a state analogous

to the hybernal sleep of some of the reptiles. The cyst shelters them

from cold and draught, and, when heat and moisture are restored, they

resume their active vitality. The motions of the Infusoria are probably

automatic, and in some instances consensual; they have neither true

eyespecks, though their whole body seems to be conscious of light and

darkness; nor have they ears; and, with the exception of touch, which

the Vorticellæ have in a marvellous degree, it may be doubted whether

the Infusoria have any organs of sense whatever, though they avoid

obstacles and never jostle one another. The vibrations of their cilia

are involuntary as in plants, an instance of the many analogies which

perpetually occur between the lowest tribes of the two great kingdoms of

nature. In both there are examples of propagation by bisection,

conjugation, budding, and the alternation of generation, which occurs

more frequently among Protozoa than among any other class of animals.

There is a perfect resemblance between Zoospores and Protozoa; they both

cease to move, the Zoospore when it secretes its cellulose coat and

becomes a winter or resting spore, the Protozoon previous to encysting,

a process presumed to be universal among that class of animals, before

subdivision or reproduction begins. It is the dried cysts or germs of

the Infusoria that float in the atmosphere as winter spores do, and it

is believed that, like the fungi, the same germs may develope themselves

into several different forms according to the nature of the liquid into

which they may chance to be deposited; consequently, it is not necessary

that the variety of germs should be very great, although the Infusoria

themselves are of numerous forms.[22]

The Infusoria, the smallest of beings, apparently so insignificant, and

for the most part invisible to the unaided eye, have high functions

assigned to them in the economy of nature. They ‘are useful for

devouring and assimilating the particles of decaying animal and

vegetable matter from their incredible numbers, universal distribution,

and insatiable voracity—they are the invisible scavengers for the

salubrity of the atmosphere. They perform a still more important office

in preventing the gradual diminution of the present amount of organic

matter upon the earth. For, when this matter is dissolved or suspended

in water in that state of comminution and decay, which immediately

precedes its final decomposition into the elementary gases, and its

consequent return from the organic to the inorganic world, these wakeful

members of Nature’s invisible police are everywhere ready to arrest the

fugitive organic particles, and turn them back into an ascending stream

of animal life. Having converted the dead and decomposing matter into

their own living tissues, they themselves become the food of larger

Infusoria, as the Rotifera and numerous other small animals, which, in

their turn, are devoured by larger animals as fishes, and thus a pabulum

fit for the nourishment of the highest organized beings is brought back

by a short route from the extremity of the realms of organized

matter.’[23]