occupied by the mouth, which opens directly into the interior cavity or stomach. The mouth is usually surrounded by a fringe of tentacles, which, in many species, in the Sea-Anemone for instance, spread in imitation of the petals of a flower. But these petals close at once upon any small animal that alights upon them, not merely detaining the victim, as do the irritable leaves of the Venus's Fly-trap, but promptly conveying it to the capacious maw, where it is digested at leisure. The polyps are not jelly-like in consistence, as is often stated; their texture is commonly fleshy or quite firm, so that they are capable of exerting considerable force. Nor are they, for the most part, invisible animalcules. Some, indeed, are microscopic; but many of the common sorts are half an inch in width; others measure two or three inches, and some of the Actinias are even a foot and a half in diameter, when their disk is spread. Though by no means the minutest, they are among the simplest of animals; for the Rotiferæ, and even the Polygastric Infusoria, appear to have a more complicated structure. Some of them move about freely in the water, their tentacles serving for locomotive as well as prehensile organs. But the greater number are firmly attached to the rocks, or some other convenient support, to which they cling with the tenacity of an officeholder, while they gorge themselves with such pickings as fall within their reach. Some polyps, such as the Hydra, it is well known, may be turned inside out, like the finger of a glove, or as the pliant office-holder turns his coat when the ins and the outs change places, - and still feed and digest unconcernedly, and thrive and batten in all respects just as well as before. Such is the simple zoöphyte. Some, even of the proper coral-polyps, remain in this independent, single state all their lives long, are solitary individuals, like the Actinia or Sea-Anemone; when their only resemblance to plants lies in the floral form which their spreading tentacles or rays simulate. From the separate polyp of this sort, there are all possible varieties and degrees of complexity, up to those living and branching masses in which hundreds of thousands of individuals are congregated and united. But the myriads which compose the coral-tree, or mass, however extensive, are all the progeny of a single polyp ancestor, in which the offspring for generation after generation remain connected with the parent. How this is brought about, so that the simple zoöphyte becomes a united family, and in time a body corporate, may now be considered. Rightly to understand this, we must contemplate the various modes of reproduction in these simpler animals, modes which appear to be the more varied and curious as we descend in the scale, beginning with that peculiar operation, so characteristic of the very lowest races, in which the simple polyps "go halves " by what the physiologists term fissiparous reproduction. In this way division is made to accomplish the ordinary result of union. A solitary individual splits up into two, each having an equal claim to be considered the parent of the other, and each equally capable of further multiplication by this odd way of pairing. This is one of the methods by which the proper Infusoria multiply at such a rapid rate. Among zoophytes, if the Hydra does not propagate exactly after this fashion, it is capable of doing so with a little adventitious aid, as was shown by those well known experiments of Trembley, who kindly assisted nature by cutting full grown individuals in pieces, and amused himself by observing each portion become a perfect Hydra ;-the tail end, in the course of two or three days, producing a head, and the head end completing itself posteriorly by a tail. In case of a three-fold division, not only will the tail produce a head and the head a tail, but a head will grow from one end of the middle section and a tail from the other, so that the animal is speedily completed in triplicate. Continuing his experiments, Trembley found that "two polyps may be made to change heads, for the head of one may be engrafted on the body of another"; and if the tail of one individual be placed in the mouth of another, the two heterogeneous extremities readily unite, so as to confound all our notions of personal identity. It cannot further surprise us that animals so indifferent whether they wear their own heads or their neighbours' should be equally indifferent whether they have any heads at all. Our author accordingly informs us, that certain aggregate zoöphytes of the order Hydroidea cast their heads at pleasure, as a lobster does his shell, or a tree its leaves in autumn; new ones springing up again after a short interval, fresh and young, to supply the place of those which were effete or addled. Thus, in a Tubularia, Mr. Harvey observed, after he had kept his specimens two days, that they began to look unhealthy, and on the third, "the heads were all thrown off and lay on the bottom of the vessel." After three days more, fresh water having been supplied, the polyps were again complete. Reproduction by spontaneous fission, however, does not explain how the single polyp becomes an aggregate; but the next, the gemmiparous, mode does. The budding process is nearly as universal in zoöphytes as in the vegetable kingdom. The simplest case of gemmiparous propagation in polyps scarcely differs essentially from that by spontaneous fission, except that the distinction between parent and offspring is manifest. Take the Hydra, for example; although it sometimes breeds ova, after a more decidedly animal fashion, yet, for the most part, the young simply pullulate from the side of the parent. "A minute protuberance first begins to rise on the surface; it lengthens and becomes a rudimentary branchlet, with a tubular axis connecting with the tubular cavity of the parent; shortly one or more tentacles begin to appear at the summit of the forming branchlet, and soon the number is completed, and the young polyp is perfected. It remains for a while attached; but, when matured, the young leaves the parent to swim at large and give birth to other young. They breed rapidly, and frequently new shoots commence before the animal is detached from the parent; and occasionally sprout on sprout is thus added, till a small compound group is formed." - p. 24. This is just the way, locomotion excepted, in which the plants multiply in a bed of tulips, and in which the common bulblet-bearing lily of our gardens produces its buds or bulbs above ground, which separate, as independent plantlets, as soon as they are formed. As in the herb or tree the bud or offspring which remains united with the parent stem forms a branch, so likewise the continued adhesion of the budding polyp-progeny to the parent, and the successive development in this way of new individuals that do not acquire complete independence, produce at length the branching zoöphyte. Each coral-tree commenced from a single polyp, just as the oak from an acorn; the branching mass in either case has arisen from the development of buds for generation after generation in union with the parent stock. And just as the branch of the growing tree, having expanded its leaves, renders its filial contributions to the mother stem, so the young persistent polyp, still sharing the maternal nourishment, "extends its arms, and begins its contributions to the bodycoralline," as soon as its mouth and tentacles are formed. "The first polyp with which the zoophyte commences thus gives out a bud, and this another; and so a succession is formed, and the little stem is gradually lengthened; branchlets grow out, and the plume, or miniature tree, is finally completed. The whole may be the work of a few weeks or months, though they usually continue budding and growing for some years. Before the zoophyte has reached its limits in size, the number of polyps sometimes becomes immensely large. In a single specimen of Plumularia collected by the author in the East Indies, there are about 12,000 polyps to each plumose branch; and, as the whole zoophyte, three feet long, bears these plumes, on an average every half inch, on opposite sides, the whole number of polyps is not short of eight millions; all the offspring of a single germ, and produced by successive buddings."- p. 24. "The several polyps in a compound zoöphyte eat and digest separately, and generally carry on as individuals the processes of reproduction and aëration; yet all aid in the growth of the common mass, though each contributes more especially to its own nutriment and the part immediately adjoining. Although their visceral cavities are distinct, there are numerous communications between those of adjoining polyps, and the fluids may pass more or less freely from one to the other. An injury to one part of a zoophyte is felt by the polyps some distance around, but not always through the whole mass. On pressing the tip of a branch of a large Alcyonium, in the Feejees, there was an immediate contraction of every polyp through the whole zoöphyte, although extending to a breadth of four feet.”—pp. 14, 15. The coral is, therefore, a body-corporate, or community, -not by any means constituted, however, on the democratic principle of the association of originally independent individuals for the promotion of common objects, but really formed on the patriarchal system, an analogy which we commend to the notice of writers on the theory of govern It is a sort of natural Fourier association, inasmuch as the gatherings of each are shared by all, although here, just as in its analogue, it turns out on examination that each individual is "more especially" occupied in taking care of itself. The members of the community not only feed at a common table, as at a corporation dinner, but have, moreover, the inestimable advantage of a corporate digestion. There is, however, considerable diversity in this respect, the burden of digestion being sometimes thrown upon the public, and sometimes borne by the individual. In many species, where the stomachs of the young polyps at first communicate freely with that of the parent, the opening is afterwards closed, and the younger members of the family are left to their own resources. In others, there is such free and open intercommunication, "that adjacent polyps have scarcely any thing but a mouth which can be said to be private property." The whole is, as it were, one manifold ramified stomach, fed by a million of mouths. This system is eminently favorable to density of population; which in these commonwealths sometimes defies all reckoning. The estimated number in one of the minuter zoöphytes has been mentioned in a former extract; the subjoined paragraph gives an idea of the populousness of some of the larger, dome-shaped corals. "Calculating the number of polyps that are united in a single Astræa dome, twelve feet in diameter, each covering a square half inch, we find it exceeding one hundred thousand; and in a Porites of the same dimensions, in which the animals are under a line in breadth, the number exceeds five and a half millions; there are here, consequently, five and a half millions of mouths and stomachs to a single zoöphyte, contributing together to the growth of the mass, by eating, and growing, and budding.". p. 60. All polyps do not form coral; nor is there any difference in structure or well marked line of distinction to be drawn between those that produce it and those that do not. Some remain soft and fleshy throughout; some acquire in their older portions the consistence of cartilage or horn; others secrete a few scattered granules of lime; and from these there are gradual transitions up to the proper coral-inaking species, whose secretions form a solid framework to the animal. Quite erroneous, too, is the common opinion, that the coral is a calcareous exudation from the surface of the polyps; it is an internal secretion, analogous rather to the skeleton of a vertebrate than to the shell of a molluscous animal. It is not like a beehive, a collection of cells which the animals have built, and in which they live. On the contrary, the coral is contained within the body of the polyp, where it is generally concealed from view, or covered by the animal tissues, at least in the living part of the coral branch. The dead coral exhibits only the skeleton, or calcareous |
