Зображення сторінки



THERE is an old aphorism which the young colt is brought forth. The says that “all life comes from an same is true of the eggs of all the egg "--omne vivum ex ovo; but this, other quadrupeds and of viviparous like a good many other old aphorisms,is animals in general. only a convenient and attractive way An egg, therefore, like the seed of of stating a falsehood. It is very a plant, is the germ from which the true that almost all animals, from embryo is developed. It may have man down to the mollusk, pass a shell, or it may not; it may be through the egg stage at an early comparatively large, like birds' eggs, period of their existence; but we or it may be so small as to be with purpose to show our readers in this difficulty discerned by the naked eye. article that there are others which When it is first formed it is simply an appear to be sometimes exempted aggregation of fluid matter, very mi. from the common lot of their kind, nute in size, and exceedingly simple and which indeed come into the world in structure. By degrees this fluid is in such curious fashions that we may transformed into the small particles almost say of them, in the words of or granules which form the yolk; Topsey, that they “ never were born; the yolk shapes itself into a multitude 'spect they growed.

of cells-little microscopic bodies conTo begin with, what is an egg? sisting of an external membrane, or According to the popular idea, it is cell-wall, and of an inner nucleus, an oval-shaped body, consisting of a which may be either solid or fluid; hard, thin shell inclosing a whitish and in due process of time a number substance called the albumen, within of cells combine and form a living bewhich is a yellowish matter called the ing. The albumen, or - white," is, yolk; it is the embryo form of the like the shell, an accessory. It peryoung of birds and some other ani- forms important functions in the demals, which finally emerge from the velopment of the young from the shell after the egg has been acted germ, but we will not stop to explain upon for some time by the heat of the them here ; the true egg is the yolk. parent's body. Now this definition In the lowest forms of animal life the may do well enough as a loose de- egg is a mere cell, with a light spot in scription of the more familiar varie. one part of it, and the creature which ties of eggs, but it will not do for all. is developed from it is almost as simIt will perhaps surprise the unscien- ple in structure as the egg itself. tific reader to be told that every ani- The ordinary mode of reproduction, mal whatever produces eggs. A as we have already said, is by the for. “ mare's nest” is the popular expres- mation of an egg in the body of the sion of a myth, an absurdity; but parent, from which the young may be mare's eggs are no myths ; they are hatched either before or after they just as real as hen's eggs; only we are brought into the world. But never see them, because they are there are certain of the lower orders of hatched in the parent's body before animals which sometimes multiply and

perpetuate their kind in other ways It is extremely sensitive, not only also. Professor Henry James Clark, shrinking from the slightest touch, of Harvard University, has lately but even drawing in its tentacles if so published an interesting treatise * on much as a dark cloud passes over it. animal development, in which he gives Anemones may be found, say the ausome curious instances of the phenom- thors of “Sea-side Studies," “ in any ena to which we refer. We have small pools about the rocks which are drawn a good deal of what we have flooded by the tide at high water. just said about the structure of eggs Their favorite haunts, howerer, where from his valuable work, and we pur- they occur in greatest quantity, are pose now to follow him in his remarks more difficult to reach ; but the curiupon the processes of reproduction by ous in such matters will be well what is called budding and division. rewarded, even at the risk of wet feet

and a slippery scramble over rocks Let us look first at that exceeding- covered with damp sea-weed, by a ly beautiful and wonderful animal glimpse into their more crowded commonly called the sea anemone, on abodes. Such a grotto is to be found account of the delicate fringed flow. on the rocks of East Point'at Nahant. er so much loved by poets. You It can only be reached at low tide, may often find it on our coasts con- and then one is obliged to creep on tracted into a lump of gelatinous sub- hands and knees to its entrance in stance looking like whitish-brown jel- order to see through its entire length; ly; † watch it for a while, and you but its whole interior is studded with will see the body rise slightly, while a these animals, and as they are of vadelicate crown of tentacles, or feelers, rious hues, pink, brown, orange, pursteals out at the top. The jelly-like ple, or pure white, the effect is like mass continues to increase in height, that of brightly-colored mosaics set in and the wreath of tentacles gradually the roof and walls. When the sun expands. Soon you will perceive that strikes through from the opposite exthis graceful fringe surrounds a wide tremity of this grotto, which is open at opening; this is the animal's mouth. both ends, lighting up its living moWhen expanded to its full size the saic-work, and showing the play of the anemone is about three or four inches soft fringes whenever the animals are in beight. The body consists of a open, it would be difficult to find any cylindrical gelatinous bag, the bottom artificial grotto to compare with it in of which is flat and slightly spreading beauty. There is another of the at the margin. The upper edge of same kind on Saunders's ledge, formthis bag is turned in, so as to form a ed by a large boulder resting on two sack within a sack; this is the stom- rocky ledges, leaving a little cave beach. The whole summit of the body neath, lined in the same way with is crowned by the soft plumy fringes variously-colored sea anemones, so which give it such a remarkable re- closely studded over its walls that the semblance to a flower. At the base it surface of the rock is completely hidhas a set of powerful muscles, by which den. They are, however, to be found it attaches itself to rocks and shells so in larger or smaller clusters, or scatfirmly that it can hardly be removed tered singly, in any rocky fissures without injury. Another set of mus. , overhung by sea-weed and accessible cles enables it to contract itself almost to the tide at high water." instantaneously into a shapeless lump. •Mr. Gosse, in his “ History of

British Sea Anemones and Corals,” ** Mind in Natare; or, The Origin of Life mentions the existence of a singular

connection between a certain variety Sea-side Studies in Natural History.". By of these animals and a species of ber

roit crab, that lives in the deserted

and the Mode of Development of Animals." bro, New York: D. Appleton & Co.

Elizabeth and Alexander Agassiz.
Hickour & Pieido. 1865.

[ocr errors]

shell of a mollusk. An anemone is may see, growing out of the lower part always found attached to the shell of the body of the anemone, and as a which the crab inhabits, and is so general thing near the edge of the placed that its fringed mouth comes basal disc by which it attaches itself just below the mouth of the crab. to the shell or rock, little rounded Whatever food comes within reach of protuberances, like buds; well, they either animal can, therefore, be shared are buds—the buds of young anemoin common. The crab is so far from nes. In a short time six small tentacles objecting to this community of goods make their appearance on the top of that he seems unhappy without his each bud. A minute oblong aperture companion. Though he is a hermit, opens in the midst of them. A digesthe is not exempt from the common ive cavity is formed. The curious lot of housekeepers ; he submits every internal structure of the animal now and then to the trouble of moving- (which we have not space here to deday.

scribe) is gradually developed. The Mr. Gosse observed one in the bud becomes elongated and enlarged act of changing houses. No sooner every way. The tentacles multihad be taken possession of the new ply; the small aperture grows into a shell than he began removing the mouth; and finally the young anemanemone from the old one, running one drops off from its parent and his claw under it to separate it from floats away to shift for itself. Prothe shell, and then bringing it to the fessor Clark has seen as many as new house, where, having placed it in twenty thus detach themselves in the its customary position, he held it course of a single month. This is the down until it had attached itself, and process of generation by budding or now and then pressed it closer, or gemmation, of which we spoke on a gave it a pat to hasten the process. previous page. In another instance, observed by Mr. But we have not yet exhausted the Holdsworth, the crab, after vainly try. list of wonders displayed by this exing for more than an hour to remove traordinary plant-animal. We have his companion anemone, deserted his seen that it has at least two ways of being new quarters and went back to the born ; what will our readers say when old, rather than submit to a separ, we assure them that it has not only a ation.

two but four? The remaining two The anemone, for all that it is so both come under the head of what is delicate and graceful in appearance, called voluntary self-division. One is a gluttonous little beast, eats raw of them is strikingly like the propagameat in the aquarium, and when upon tion of plants by cuttings. Little its native coast sucks mussels and pieces break off from the anemone at cockles out of their shells. Queer the base and float away. For a compound of plant and animal in ap- long time they give no sign of life ; pearance, its natural kingdom seems but when they have recovered, so to still more doubtful than ever if we speak, from the shock of separation, watch it while it is undergoing certain they begin to shoot out their tentacles processes of reproduction. It does and grow up into perfect individuals. indeed generally produce its young The fourth method of generation is by maternal gestation; eggs are still more wonderful. Now and then formed in the cavity that surrounds you find an anemone whose upper its stomach, and at the proper time disc is contracted in a peculiar manthe young swim out of the parent's ner at opposite sides. The conmouth. But it has other modes of traction increases until the disc loses propagation, one of which is almost its circular form and presents the exactly like the process of raising shape of the figure 8. The two plants from suckers. Very often you halves of the 8 next separate, and you

hare an anemone with two mouths, and a long funnel-shaped throat reacheach surrounded by its own set of ten- es from it to the digestive cavity. Optacles. Then the processes of con- posite the mouth there is a globular striction and separation continue all cavity, from which a tube extends to down the body of the animal from the lower extremity of the body. The summit to base, and the result is two cavity seems to perform the functions perfect anemones, each complete in of a heart, and the tube takes the place its organization. It is well that the of veins and arteries. Once in threelower orders of creatures have none quarters of a minute this heart-like of the laws of inheritance and primo- organ contracts and forces the fluid geniture that bother mankind, or such which it contains into the tube; the irregular methods of coming into the latter in its turn, after expanding very world might breed a great deal of sensibly to receive the flow, contracts trouble among them. Here, for in- and returns it to the heart. stance, you have two anemones, which T he stentor propagates by budding, we will call A and B, formed by the like the anemone. The first change splitting asunder of a single individ- that takes place is a division of this ual; what relation are they to each contractile vesicle into two distinct other? Are they brother and sister organs at about mid-height of the body, or parent and child? And if the latter, the lower portion developing a globuLow is any one to decide which is the lar cavity like the upper one. Soon parent? Then suppose A raises off after this a shallow pit opens in the spring in the usual way from eggs, side of the stentor, in a line with the what relation are these young to B? new vesicle. This pit is the future Are they sisters, or pieces, or grand- mouth. A throat or csophagus is children?

next fashioned ; and all being ready Let us now look at another animal, for the accommodation of the new the stentor, or trumpet-animalcule. animal the process of division begins, This is a minute infusorian, very com- and goes on so rapidly that it is all mon in ponds and ditches, where it done in about two hours. forms colonies on the stems of water- A still more curious animal, in some weeds or submerged sticks and stones. respects, than either of those we have Some of the varieties have a deep just mentioned is the hydra, one of blue color, and a settlement of them the simplest of the zoophytes. To looks very much like a patch of blue all intents and purposes it is nothing mould. The stentor is shaped like a but a narrow sack, about half an inch little tube, about one-sixteenth of an in length, open at one end, where the inch in length, spread out at the upper mouth is situated, and attaching itself end like a trumpet, and tapering at by the other to pond-lilies, duck-weeds, the lower almost to a point. When or stones on the margins of lakes. it has fixed upon a place of abode, it Around the mouth it has from five to constructs a domicile, consisting of a eight slender tentacles, which are used gelatinous sheath, perhaps half as high as feelers and for the purpose of scizing as itself. It lives inside this sheath, the food. What it does with its food with its smaller extremity attached to after it has swallowed it is, strange as the bottom of it, and its wide, funnel- the statement may sound, a question shaped end projecting above the top. to which naturalists have not yet When disturbed it retreats into the found a satisfactory answer; for the house and shrinks into a globular hydra has no digestive organs, and its mass. The disc of the trumpet end stomach is merely a pouch formed by is not perfectly regular; on one side the folding in of the outer skin. It the edge turns inward so as to form a has no glands, no mucous membrane, notch, and curls upon itself in a spiral no appliances of any sort for the perform. Within this spiral is the mouth, formance of the chemical process which we call digestion. You may pect that animals which care so little turn a hydra inside out and it will about their individuality that two spccget along just as well as it did before, imens can be turned into one, would and swallow its prey with just as good be equally ready to multiply theman appetite. The French naturalist selves by the simple process of being Trembley was the first to notice this cut to pieces. In other words, you remarkable fact. With the blunt end may make one hydra out of two, or of a small needle he pushed the bot. two out of one, just as you please. tom of the sack through the body and M. Trembley divided them in every out at the mouth, just as you would conceivable manner. He cut them invert a stocking. He found that the in two, and, instead of dying. one half animal righted itself as soon as it was shot out a new head and the other leít alone; so he repeated the opera- developed a new tail. Ile sliced them tion, and this time made use of per- into thin rings, and each slice swam suasion, in the form of a bristle run away, got itself a set of tentacles, crosswise through the body, to induce and grew into a perfectly formed inthe victim to remain inside out. In dividual. He split them into thin the course of a few days its interior longitudinal strips, and each strip reand exterior departments were thor- produced what was wanting to give it oughly reorganized, and it ate as if a complete body. Some he split only nothing had happened. Trembley part way down from the mouth, and next undertook to engraft one individ- the result was a hydra, like the fabled ual upon another! For this purpose monster, with many heads. The fahe crammed the tail of one deep down mous cat with nine lives is nothing into the cavity of another, and, in order to these little zoophytes. They seem to hold them in their position, stuck a sublimely indifferent not only to the bristle through both. What was his most fearful wounds, but even to dissurprise to find them, some hours ease and, we are tempted to add, deafterward, still spitted upon the bris- composition itself. A part of the body tle, but hanging side by side instead of decays, and the hydra simply drops it one within the other! How they had off, like a worn-out garment, and lives got into such a position he could not on as if it had lost nothing. imagine. He arranged another pair, If it can do all this, we need not and on watching them the mystery wonder that it can reproduce its kind was solved. The inner one first drew by budding. Indeed, after we have up its tail and pushed it out through seen a living creature split itself up the hole in the outer one's side where into a dozen distinct individuals any the bristle entered. Then it pulled other process of generation must seem its head out after the tail, and sliding tame by comparison. At certain seaalong the spit completely freed itself sons of the year very few hydras can be from its companion. This it repeat- found which have not one, two, or three ed as often as the experiment was young ones growing out of their bodies. tried in that way. It then occurred The budding begins in the form of a to M. Trembley that if the inner simple bulging from the side of the hydra were turned inside out, so as to parent, something like a wart. This bring the stomachs of the two animals is gradually elongated, and after a time in contact, union would take place tentacles sprout from the free end, and more readily ; and so it proved. The a mouth is formed. The young is little creatures seemed much pleased now in a condition to seek its own with the arrangement, and made no prey. Its independence is finally acattempt to escape. In a short time complished by a constriction of the they were united as one body, and en- base of the new body at the point joyed their food in common.

where it is attached to the old stock, It was perhaps only natural to ex- until finally it cuts itself off. Before

« НазадПродовжити »