viduality in the division of its body to form other individuals. At one stage in its development, namely, when filled with the miniature "spindles" (Fig. 1, a) into which it has divided itself, the gregarina or amoeba in reality becomes a colony or aggregation of beings. But such a tendency is at the most transitory, and the temporary colony speedily resolves itself into a diffused and separated mass of young organisms, whose individuality, and indeed whose whole existence, is due to the destruction of those of their parent. In another sense, the amoeba may occasionally show this tendency to lose its single and defined individuality in that of the compound colony. For occasionally particles or offshoots of the amoeba's protoplasmic body detach themselves therefrom, and pass away like precocious emigrants from the parent-frame to assume all the functions of amoeba on their own account. In this way, and through the exercise of the simplest reproductive process we know of—namely, that of "fission," or simple division of an animal's body into two or more new beings-the amoeba-body converts itself from a single "individual" into a mothercolony, with offshoots and emigrants seeking a life and existence of their own. And, last of all, in the gregarina itself, we may find certain important variations in structure which seem to threaten the destruction of the individualism of its body, and to merge the individual in the crowd. For we know not merely of gregarinæ which consist apparently of but one mass of protoplasm, as already described, but of others which exhibit a division of body into two (Fig. 1, d) or even three compartments. What the significance of this tendency to division or segregation may be, is yet matter of conjecture; but at first sight its meaning would seem to foreshadow the same destruction of individual constitution which, in their development, these organisms unquestionably exhibit.

Even in the lowest animals, each consisting of a minute mass of protoplasm, there is thus observed a tendency, at some period or other of their life-history, to depart from the single state, and by division, or, as it is named, "segregation," of their substance, to form a "colonial " or compound organisation. But even in the lower confines of animal life, which harbour the amoebae and gregarinæ as typical tenants, are represented states and phases of organisation which are purely and typically "colonial." Thus, that low form of life known as Myxodictyum normally exists as a collection of protoplasmic particles, such as would be exactly imitated if a number of amoeba banded and fused themselves together. It is equally interesting to note that the vast majority of the Foraminifera (Fig. 3), or "chalk-animalcules," are to be regarded as exhibit

ing a compound constitution. For, in these animalcules, which are as a rule of compound nature (Fig. 3, b), the growth of new divisions of the shell takes place by a process of budding, and through the production of new protoplasmic units which remain organically connected with the

original mass. Nor are the lowest plants to be left out of consideration in this recital of primitive colony-making. The cryptogamic botanist well knows certain green specks of microscopic size, each called Chlamydomonas, which swim freely in fresh waters, by means of two long cilia, or miniature eyelashes, projecting from one extremity of the body. Now, there exist in stagnant waters certain other curious bodies, long known as "Globe-animalcules," before they were ascertained to be lower plants. Each of these bodies is scientifically named a Volvox (Fig. 4, d), and appears to consist of a hollow globe or sphere, covered with innumerable little specks of bright green, and swimming freely through the water by the waving action of the fine cilia which fringe its body. More minutely examined, this rolling globe is found to consist of a col

lection of little

green bodies,

each of which,

in all essential

details, exactly f

resembles a

single chlamy

FIG. 3.

FORAMINIFERA.

b

a

b

domonas. The J

filaments fring

C

ing the volvox

FIG. 4. VOLVOX (d) AND VARICUS ANIMALCULES.

are in reality pairs of cilia like those of chlamydomonas, and are attached to the little green bodies aforesaid. Thus volvox, so far from being an animal, is, firstly, a rootless lower plant; and, secondly,

so far from being one plant, volvox is in reality a colony of the lowest members of the vegetable world. There are many other Alga (or lowest plants) which resemble volvox in their compound nature; and thus the beginnings of plant-life appear to present us with a tendency towards colonisation similar to that which faces us on the threshold of the other series of living beings.

In the curious group of the sponges (fig. 5), we may find our next convenient halting-place in our researches into animal individuality

and its variations. From forming the bête noire of the naturalist of former years, who was troubled in his mind as to the animal or plant nature of the sponges, to occupying a singular and anomalous position in the animal classifications of to-day, this group of organisms has attained a well-merited celebrity. The living parts of a sponge that is to say, the parts which form and make the spongeframework, and which alone concern us in our present investigation -consist of masses of protoplasm, which are in their way strictly comparable to the minute bodies, or "cells," of which our own tissues are built up. A sponge, as to its living parts, is a mass of protoplasmic cells, "some of which," as Huxley puts it, "have all the characters of Amab; while others are no less similar to monads " -these latter being microscopic masses of protoplasm, furnished, like chlamydomonas, with two waving cilia. The comparison of a sponge to a kind of "submarine Venice," with its canals, along the banks of which the inhabitants (or masses of protoplasm) reside, and through which flow the water-currents bringing particles of nourish

sense.

ment to these denizens, is therefore seen to be fully justifiable in one Still more justifiable and appropriate would such a metaphor be, could we prove that the sponge was in reality what the simile indicates, namely, a colony of animals-seeing that the comparison of the sponge to the Adriatic capital derives its whole force from the assumption that its personality, like that of the city, is compound, and not that of the element or unit. As we shall hereafter see more plainly, the sponge must be judged, like every other living being, not by its appearance or by what it simulates, but by what it originated from. As an apparent collection of organisms, it might well be regarded as a veritable colony; on other grounds, the sponge might appear as rightfully entitled to be considered as single and undivided an animal unit as a man. The grounds on which these opinions are based need not now be specified, but the history of how a sponge grows, finds its appropriate place at this stage of our inquiry. The most typical sponges grow each from an egg (Fig. 5, 1), which passes through characteristic stages of development (2, 3, 4), and finally becomes a cup-shaped body (5), possessing a double wall (c, d), the cavity of the cup opening outwardly by a distinct mouth (m). Then pores or openings (7, p) are formed in the wall of this cup, placing its interior in a new fashion in communication with the outside world. The outer wall of the cup, and the inner wall likewise, consist of cells; and those of the inner wall finally come to possess cilia, which, by their constant motion, cause currents of water to flow into the inside of the cup through the pores, and outwards by its mouth.

The nourishment of a sponge is subserved by these water currents, bringing food and oxygen to its living cells; and the simple or cup-shaped sponges (Fig. 5, 7), of which many species are known, exhibit a history resembling that of which the outlines have just been sketched. The horny sponges, the skeletons of certain species of which we use in our domiciles, may and do develope into organisms of a more complex character than the cupsponges present, and they may also originate otherwise than from eggs. The common green fresh-water Spongilla, found growing on the sides of canal locks and in similar situations, illustrates the latter form of development. This species propagates its kind by veritable buds, whilst it also produces eggs; and another curious fact, possessing a significant bearing on the individuality of the sponges, consists in the observation that when two Spongilla are placed in contact they merge together into one. They may also be divided artificially, or may separate spontaneously into two or more organisms,

each of which will lead an independent existence. The sponges, then, may be hereafter referred to as a group of animals which, whilst originating from eggs, as do higher beings, yet retain much of that tendency to segregation and separation into distinct and elementary parts which we may reasonably maintain is a primitive and fundamental character of all living beings.

Nearly allied to the sponges are the little freshwater polypes named Hydra (Fig. 6), and the marine plant-like organisms familiarly

Young hydra are represented budding from the parent in each figure.) and segregation of body which, at the best, are but dimly marked in lower organisms. The hydra, existing as a little green tubular body-attached by one extremity to a water weed, and exhibiting at the free end a mouth and tentacles-at certain seasons exhibits a growth of small projections on its sides. As these projections increase in size, they grow

FIG. 7. ZOOPHYTES. 6 and d, magnified portions of a and c respectively.

into the likeness of young hydræ (Fig. 6), each developing a mouth and tentacles, and possessing, so long as they adhere to the parent body, free communication with the interior of the latter. These budded