Volume 3 — CURIOSITIES OF ANIMAL LIFE.

There is an old aphorism which says that "all life comes from an egg"--omne vivum ex ovo; but this, like a good many other old aphorisms, is only a convenient and attractive way of stating a falsehood. It is very true that almost all animals, from man down to the mollusk, pass through the egg stage at an early period of their existence; but we purpose to show our readers in this article that there are others which appear to be sometimes exempted from the common lot of their kind, and which indeed come into the world in such curious fashions that we may almost say of them, in the words of Topsey, that they "never were born; 'spect they growed. "

To begin with, what is an egg? According to the popular idea, it is an oval-shaped body, consisting of a hard, thin shell inclosing a whitish substance called the albumen, within which is a yellowish matter called the yolk; it is the embryo form of the young of birds and some other animals, which finally emerge from the shell after the egg has been acted upon for some time by the heat of the parent's body. Now this definition may do well enough as a loose description of the more familiar varieties of eggs, but it will not do for all. It will perhaps surprise the unscientific reader to be told that every animal whatever produces eggs. A "mare's nest" is the popular expression of a myth, an absurdity; but mare's eggs are no myths; they are just as real as hen's eggs; only we never see them, because they are hatched in the parent's body before the young colt is brought forth. The same is true of the eggs of all the other quadrupeds and of viviparous animals in general.

An egg, therefore, like the seed of a plant, is the germ from which the embryo is developed. It may have a shell, or it may not; it may be comparatively large, like birds' eggs, or it may be so small as to be with difficulty discerned by the naked eye. When it is first formed it is simply an aggregation of fluid matter, very minute in size, and exceedingly simple in structure. By degrees this fluid is transformed into the small particles or granules which form the yolk; the yolk shapes itself into a multitude of cells--little microscopic bodies consisting of an external membrane, or cell-wall, and of an inner nucleus, which may be either solid or fluid; and in due process of time a number of cells combine and form a living being. The albumen, or "white," is, like the shell, an accessory. It performs important functions in the development of the young from the germ, but we will not stop to explain them here; the true egg is the yolk. In the lowest forms of animal life the egg is a mere cell, with a light spot in one part of it, and the creature which is developed from it is almost as simple in structure as the egg itself.

The ordinary mode of reproduction, as we have already said, is by the formation of an egg in the body of the parent, from which the young may be hatched either before or after they are brought into the world. But there are certain of the lower orders of animals which sometimes multiply and {233} perpetuate their kind in other ways also. Professor Henry James Clark, of Harvard University, has lately published an interesting treatise [Footnote 44] on animal development, in which he gives some curious instances of the phenomena to which we refer. We have drawn a good deal of what we have just said about the structure of eggs from his valuable work, and we purpose now to follow him in his remarks upon the processes of reproduction by what is called budding and division.

Let us look first at that exceedingly beautiful and wonderful animal commonly called the sea anemone, on account of the delicate fringed flower so much loved by poets. You may often find it on our coasts contracted into a lump of gelatinous substance looking like whitish-brown jelly; [Footnote 45] watch it for a while, and you will see the body rise slightly, while a delicate crown of tentacles, or feelers, steals out at the top. The jelly-like mass continues to increase in height, and the wreath of tentacles gradually expands. Soon you will perceive that this graceful fringe surrounds a wide opening; this is the animal's mouth. When expanded to its full size the anemone is about three or four inches in height. The body consists of a cylindrical gelatinous bag, the bottom of which is flat and slightly spreading at the margin. The upper edge of this bag is turned in, so as to form a sack within a sack; this is the stomach. The whole summit of the body is crowned by the soft plumy fringes which give it such a remarkable resemblance to a flower. At the base it has a set of powerful muscles, by which it attaches itself to rocks and shells so firmly that it can hardly be removed without injury. Another set of muscles enables it to contract itself almost instantaneously into a shapeless lump. It is extremely sensitive, not only shrinking from the slightest touch, but even drawing in its tentacles if so much as a dark cloud passes over it. Anemones may be found, say the authors of "Sea-side Studies," "in any small pools about the rocks which are flooded by the tide at high water. Their favorite haunts, however, where they occur in greatest quantity, are more difficult to reach; but the curious in such matters will be well rewarded, even at the risk of wet feet and a slippery scramble over rocks covered with damp sea-weed, by a glimpse into their more crowded abodes. Such a grotto is to be found on the rocks of East Point at Nahant. It can only be reached at low tide, and then one is obliged to creep on hands and knees to its entrance in order to see through its entire length; but its whole interior is studded with these animals, and as they are of various hues, pink, brown, orange, purple, or pure white, the effect is like that of brightly-colored mosaics set in the roof and walls. When the sun strikes through from the opposite extremity of this grotto, which is open at both ends, lighting up its living mosaic-work, and showing the play of the soft fringes whenever the animals are open, it would be difficult to find any artificial grotto to compare with it in beauty. There is another of the same kind on Saunders's ledge, formed by a large boulder resting on two rocky ledges, leaving a little cave beneath, lined in the same way with variously-colored sea anemones, so closely studded over its walls that the surface of the rock is completely hidden. They are, however, to be found in larger or smaller clusters, or scattered singly, in any rocky fissures overhung by sea-weed and accessible to the tide at high water."

Mr. Gosse, in his "History of British Sea Anemones and Corals," mentions the existence of a singular connection between a certain variety of these animals and a species of hermit crab that lives in the deserted {234} shell of a mollusk. An anemone is always found attached to the shell which the crab inhabits, and is so placed that its fringed month comes just below the mouth of the crab. Whatever food comes within reach of either animal can, therefore, be shared in common. The crab is so far from objecting to this community of goods that he seems unhappy without his companion. Though he is a hermit, he is not exempt from the common lot of housekeepers; he submits every now and then to the trouble of moving-day.

Mr. Gosse observed one in the act of changing houses. No sooner had he taken possession of the new shell than he began removing the anemone from the old one, running his claw under it to separate it from the shell, and then bringing it to the new house, where, having placed it in its customary position, he held it down until it had attached itself, and now and then pressed it closer, or gave it a pat to hasten the process. In another instance, observed by Mr. Holdsworth, the crab, after vainly trying for more than an hour to remove his companion anemone, deserted his new quarters and went back to the old, rather than submit to a separation.

The anemone, for all that it is so delicate and graceful in appearance, is a gluttonous little beast, eats raw meat in the aquarium, and when upon its native coast sucks mussels and cockles out of their shells. Queer compound of plant and animal in appearance, its natural kingdom seems still more doubtful than ever if we watch it while it is undergoing certain processes of reproduction. It does indeed generally produce its young by maternal gestation; eggs are formed in the cavity that surrounds its stomach, and at the proper time the young swim out of the parent's mouth. But it has other modes of propagation, one of which is almost exactly like the process of raising plants from suckers. Very often you may see, growing out of the lower part of the body of the anemone, and as a general thing near the edge of the basal disc by which it attaches itself to the shell or rock, little rounded protuberances, like buds; well, they are buds--the buds of young anemones. In a short time six small tentacles make their appearance on the top of each bud. A minute oblong aperture opens in the midst of them. A digestive cavity is formed. The curious internal structure of the animal (which we have not space here to describe) is gradually developed. The bud becomes elongated and enlarged every way. The tentacles multiply; the small aperture grows into a mouth; and finally the young anemone drops off from its parent and floats away to shift for itself. Professor Clark has seen as many as twenty thus detach themselves in the course of a single month. This is the process of generation by budding or gemmation, of which we spoke on a previous page.

But we have not yet exhausted the list of wonders displayed by this extraordinary plant-animal. We have seen that it has at least two ways of being born; what will our readers say when we assure them that it has not only two but four? The remaining two both come under the head of what is called voluntary self-division. One of them is strikingly like the propagation of plants by cuttings. Little pieces break off from the anemone at the base and float away. For a long time they give no sign of life; but when they have recovered, so to speak, from the shock of separation, they begin to shoot out their tentacles and grow up into perfect individuals. The fourth method of generation is still more wonderful. Now and then you find an anemone whose upper disc is contracted in a peculiar manner at opposite sides. The contraction increases until the disc loses its circular form and presents the shape of the figure 8. The two halves of the 8 next separate, and you {235} have an anemone with two mouths, each surrounded by its own set of tentacles. Then the processes of constriction and separation continue all down the body of the animal from summit to base, and the result is two perfect anemones, each complete in its organization. It is well that the lower orders of creatures have none of the laws of inheritance and primo-geniture that bother mankind, or such irregular methods of coming into the world might breed a great deal of trouble among them. Here, for instance, you have two anemones, which we will call A and B, formed by the splitting asunder of a single individual; what relation are they to each other? Are they brother and sister or parent and child? And if the latter, how is any one to decide which is the parent? Then suppose A raises offspring in the usual way from eggs, what relation are these young to B? Are they sisters, or nieces, or grandchildren?

Let us now look at another animal, the stentor, or trumpet-animalcule. This is a minute infusorian, very common in ponds and ditches, where it forms colonies on the stems of water-weeds or submerged sticks and stones. Some of the varieties have a deep blue color, and a settlement of them looks very much like a patch of blue mould. The stentor is shaped like a little tube, about one-sixteenth of an inch in length, spread out at the upper end like a trumpet, and tapering at the lower almost to a point. When it has fixed upon a place of abode, it constructs a domicile, consisting of a gelatinous sheath, perhaps half as high as itself. It lives inside this sheath, with its smaller extremity attached to the bottom of it, and its wide, funnel-shaped end projecting above the top. When disturbed it retreats into the house and shrinks into a globular mass. The disc of the trumpet end is not perfectly regular; on one side the edge turns inward so as to form a notch, and curls upon itself in a spiral form. Within this spiral is the mouth, and a long funnel-shaped throat reaches from it to the digestive cavity. Opposite the mouth there is a globular cavity, from which a tube extends to the lower extremity of the body. The cavity seems to perform the functions of a heart, and the tube takes the place of veins and arteries. Once in three-quarters of a minute this heart-like organ contracts and forces the fluid which it contains into the tube; the latter in its turn, after expanding very sensibly to receive the flow, contracts and returns it to the heart.

The stentor propagates by budding, like the anemone. The first change that takes place is a division of this contractile vesicle into two distinct organs at about mid-height of the body, the lower portion developing a globular cavity like the upper one. Soon after this a shallow pit opens in the side of the stentor, in a line with the new vesicle. This pit is the future mouth. A throat or oesophagus is next fashioned; and all being ready for the accommodation of the new animal the process of division begins, and goes on so rapidly that it is all done in about two hours.

A still more curious animal, in some respects, than either of those we have just mentioned is the hydra, one of the simplest of the zoophytes. To all intents and purposes it is nothing but a narrow sack, about half an inch in length, open at one end, where the mouth is situated, and attaching itself by the other to pond-lilies, duck-weeds, or stones on the margins of lakes. Around the mouth it has from five to eight slender tentacles, which are used as feelers and for the purpose of seizing the food. What it does with its food after it has swallowed it is, strange as the statement may sound, a question to which naturalists have not yet found a satisfactory answer; for the hydra has no digestive organs, and its stomach is merely a pouch formed by the folding in of the outer skin. It has no glands, no mucous membrane, no appliances of any sort for the performance of the chemical process {236} which we call digestion. You may turn a hydra inside out and it will get along just as well as it did before, and swallow its prey with just as good an appetite. The French naturalist Trembley was the first to notice this remarkable fact. With the blunt end of a small needle he pushed the bottom of the sack through the body and out at the mouth, just as you would invert a stocking. He found that the animal righted itself as soon as it was left alone; so he repeated the operation, and this time made use of persuasion, in the form of a bristle run crosswise through the body, to induce the victim to remain inside out. In the course of a few days its interior and exterior departments were thoroughly reorganized, and it ate as if nothing had happened. Trembley next undertook to engraft one individual upon another! For this purpose he crammed the tail of one deep down into the cavity of another, and, in order to hold them in their position, stuck a bristle through both. What was his surprise to find them, some hours afterward, still spitted upon the bristle, but hanging side by side instead of one within the other! How they had got into such a position he could not imagine. He arranged another pair, and on watching them the mystery was solved. The inner one first drew up its tail and pushed it out through the hole in the outer one's side where the bristle entered. Then it pulled its head out after the tail, and sliding along the spit completely freed itself from its companion. This it repeated as often as the experiment was tried in that way. It then occurred to M. Trembley that if the inner hydra were turned inside out, so as to bring the stomachs of the two animals in contact, union would take place more readily; and so it proved. The little creatures seemed much pleased with the arrangement, and made no attempt to escape. In a short time they were united as one body, and enjoyed their food in common.

It was perhaps only natural to expect that animals which care so little about their individuality that two specimens can be turned into one, would be equally ready to multiply themselves by the simple process of being cut to pieces. In other words, you may make one hydra out of two, or two out of one, just as you please. M. Trembley divided them in every conceivable manner. He cut them in two, and, instead of dying, one half shot out a new head and the other developed a new tail. He sliced them into thin rings, and each slice swam away, got itself a set of tentacles, and grew into a perfectly formed individual. He split them into thin longitudinal strips, and each strip reproduced what was wanting to give it a complete body. Some he split only part way down from the mouth, and the result was a hydra, like the fabled monster, with many heads. The famous cat with nine lives is nothing to these little zoophytes. They seem sublimely indifferent not only to the most fearful wounds, but even to disease and, we are tempted to add, decomposition itself. A part of the body decays, and the hydra simply drops it off, like a worn-out garment, and lives on as if it had lost nothing.

If it can do all this, we need not wonder that it can reproduce its kind by budding. Indeed, after we have seen a living creature split itself up into a dozen distinct individuals any other process of generation must seem tame by comparison. At certain seasons of the year very few hydras can be found which have not one, two, or three young ones growing out of their bodies. The budding begins in the form of a simple bulging from the side of the parent, something like a wart. This is gradually elongated, and after a time tentacles sprout from the free end, and a mouth is formed. The young is now in a condition to seek its own prey. Its independence is finally accomplished by a constriction of the base of the new body at the point where it is attached to the old stock, until finally it cuts itself off. Before {237} this separation takes place, however, it has often begun to reproduce its own young, and so we sometimes see a large colony of hydras all connected together, like minute branching waterweed.

After all, you may say, it is not so very wonderful that a simple animal like the hydra, which has no intestines, and scarcely any special organs whatever, should be able to reproduce its lost parts, or to multiply itself by the simple processes of growth and subsequent division. Well, then, let us take a more complex creature, and we have a remarkable example at hand in a certain marine worm called myrianida fasciata. It is an inch or two in length, tapering off gradually from the head. The body is marked with numerous rings or joints, attached to which are oar-like appendages, serving not only as instruments of propulsion but also as gills, or breathing organs. An intestine extends from the head in a direct course to the posterior. Blood-vessels are arranged about it like a net-work, and connect with similar vessels in the gills. It has an organ which serves the purpose of a heart, a nervous cord swollen at every joint into knots or ganglions, and, in the head, one principal ganglion, which may be considered as the brain. Its reproductive organs are situated only in the posterior rings, and are located there in reference to the peculiar mode of generation which we are about to describe. The young worm begins to grow immediately in front of the parent's tail, that is to say, between the last joint or ring and the next before the last, and is formed by the successive growth of new rings. Before it is old enough to be cast off another appears between its anterior end and the next joint of the old stock; and so on until we have six worms at once, all strung together behind the parent, and hanging, so to speak, from one another's tails. They drop off separately, in the order of their age. Now in this case, you will observe, there must be a division of several organs--the intestine, the blood-vessels, and the nervous cord; and each of the six young must develop a heart, a brain, and a pair of eyes. An odd result of their method of growth (the first one being formed, you will remember, not behind the parent but between her last two rings) is that the eldest offspring appropriates the tail of his mother, while his five brothers and sisters have to find tails of their own. We are here tempted to indulge in a curious speculation: this first born produces its young in the same way itself was produced, and passes on its inherited tail to the next generation. The eldest born of that generation bequeaths it to the next, and so on. What becomes of that ancestral tail in the course of years? Does it at last wear out and drop off? Does the worm that bears it die after a time without leaving any children? Or is it possible that the process of entail has been going on without interruption ever since the year one of the world, and that there may be a myrianida fasciata now living with a tail as old as creation? Not very probable, certainly; but if any solution has been offered of the great tail problem, we do not happen to have heard of it.

Professor Clark also tried various experiments upon the common flat worm, or planaria, which may be found so readily in our ponds, creeping over stones and aquatic plants, and is so easily recognized by its opaque white color, and the liver-colored ramifications of its intestine. He cut the creature in two, and immediately after the operation the halves crawled away as if nothing had happened; the anterior part preceding an ideal tail, and the posterior one following an equally imaginary head and brain. He watched the pieces from day to day, and found that each reproduced its missing half by a slow process of budding and growth. This planaria may be cut into several pieces, and each will reproduce what is requisite to complete the mangled organism. If the tail of a lizard be broken off, a {238} new one will grow; and crabs, lobsters, spiders, etc., are known to replace their amputated limbs. The instances we now and then meet with of what are called monsters--two-headed dogs, calves with six legs, and, more rarely, even double-headed human beings, are examples of the phenomenon of budding--which is very common, by the way, among fishes; and there is an animalcule called the amoeba which shows a more remarkable tenacity of life than any of the other creatures we have mentioned, since you may divide and subdivide it until it is physically impossible to reduce it to particles any smaller, and yet each piece will live.

The discovery that animals may originate in so many ways independent of maternal gestation naturally suggests the inquiry whether further researches may not develop still other methods of reproduction, in which the new-born creature shall have no connection whatever with any previously existing individual. Thus we are brought back to the question which was thought to have been settled long ago, whether generation ever takes place spontaneously, as Aristotle and the old physicists supposed it did. Later naturalists, following the Italian, Redi, utterly rejected the supposition; but within the present century it has found many reputable supporters, and Professor Clark is one of them. When organic matter decays, numbers of infusoria, or microscopic plants and animals, arise in it. Where do they come from? Do the disorganized particles, set free by the process of decomposition, combine into new forms, which are then endowed with life by the direct action of Almighty power; or is the decaying substance merely the nest in which minute eggs or seeds, borne thither upon the air, or dropped by insects, find conditions suitable for their development in the ordinary natural way? The question is not easily answered. Many of these germs are so excessively minute as to defy detection. Some of the infusoria are no larger than the twenty-four-thousandth of an inch in diameter, and it is estimated that a drop of water might contain five hundred millions of them. It is obvious that the germs of such little creatures must be invisible even with the best microscope. The problem can only be solved by placing a portion of the decomposing matter under such conditions that any germs it may contain shall infallibly be killed and that none can possibly reach it; then, if infusoria appear, we shall know that they have been generated spontaneously. The great difficulty is in securing these conditions. For the development of the living forms we require both water and air. How are we to be certain that there are no living germs in the organic matter before we begin the experiment? that there are none in the water? that none are brought by the air? The action of heat has been relied upon for the destruction of germs in the organic matter and the water, and it has been sought to purify the air from them by passing it through sulphuric add; but experience has shown that sulphuric add does not kill the germs; so of course experiments performed in that way prove nothing. Professor Clark quotes a series of very delicate experiments tried by Professor Jeffries Wyman, of Harvard University, which seem to us to come nearer to proving spontaneous generation than any others with which we are acquainted. He proceeded in three different methods, as follows:

1. The organic matter, consisting of a solution of beef or mutton juice (or, in a few instances, vegetable matter), was placed in a flask fitted with a cork through which passed a glass tube. The cork was pushed deeply into the mouth of the flask, and the space above it was filled with an adhesive cement, composed of resin, wax, and varnish. The tube was drawn to a narrow neck a little way above the cork, and bent at right angles, and {239} the end of it inserted in an iron tube, where it was secured by a cement of plaster of Paris. The rest of the iron tube was filled with wires, leaving only very narrow passages between them. The solution in the flask was then boiled--in some cases as long as two hours--in order to kill any germs which might be enclosed, and to expel the air. The iron tube and wires at the same time were heated to redness. When the boiling had continued long enough the heat was withdrawn from beneath the flask, and the steam was allowed slowly to condense. As it did so, air flowed in between the red-hot wires, which had been kept at a temperature high enough, it was supposed, to destroy any germs in the air that passed through them. The flask was then hermetically sealed by fusing the glass tube with the blow-pipe. When opened, several days afterward, it was found to contain animal life.

2. A similar solution was placed in a flask the neck of which, instead of being supplied with a cork and tube, was drawn out and bent at right angles, and then fitted to the iron tube containing wires. The experiment was performed as by method No. 1, and with the same result.

3. That there might be no suspicion of imperfectly sealed joints, a solution was put into a flask with a narrow neck, and the neck itself was then closed by fusing the glass. The whole flask was then immersed in boiling water. At the expiration of a few days living infusoria were found in two instances out of four.

Now these experiments undoubtedly prove that generation sometimes occurs spontaneously, provided it be true, as Professor Clark assumes, that there was no imperfection in the closing of the flasks (which we see no reason to doubt), and that the infusorial germs are destroyed by boiling. We confess that it is hard to believe they could have survived such a heat as was applied to them in these cases; but is it certain that they could not? A writer in an English review a few years ago, whom we believe to have been Mr. G. H. Lewes, announced that he had boiled certain germs an hour and three-quarters, and yet they remained perfectly unaltered. At most, therefore, we can regard spontaneous generation as a probable phenomenon.

Whether spontaneous generation, if it occurs at all, occurs by the formation of an egg from which the animalcule is hatched, or by the immediate formation of the adult, Professor Clark does not attempt to say; but the French naturalist M. Pouchet, who is one of the foremost advocates of the theory, holds that an egg is produced first. If this is true we shall have a striking correlative to the proposition with which we began this paper: not only can living creatures be developed where no egg has been deposited, but eggs can be produced where there is no animal to lay them. Omne ovum e vivo will be no more true than Omne vivum ex ovo.

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