[ORIGINAL.]
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.
[Footnote 44: "Mind in Nature; or, The Origin of Life and the Mode of Development of Animals." 8vo. New York: D. Appleton & Co.]
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."
[Footnote 45: "Sea-side Studies in Natural History." By Elizabeth Alexander Agassiz. Boston: Ticknor & Fields. 1865.]
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.