they detach themselves from the parent stem, and become separate animals.

It is stated that, by this mode of generation, in the space of a month a single polype may be the parent of a million of descendants. Trembley observed some long branches of trees that had fallen into the water, which he describes as being as full of polypes as a peruke of hairs; and that though their innumerable arms were at work, there was no confusion amongst them.

But these animals, as is well known, do not multiply solely by germes, but also by cuttings, as they may be called; their substance is so instinct with life, that nothing appears able to destroy it—a circumstance, perhaps, arising from the nervous molecules of which it seems almost to consist. If divided transversely, each segment will become a distinct animal, send forth tentacles round its upper aperture, and close the lower one; if it is divided longitudinally, each half will form a separate tube in an hour, and begin to ply its tentacles in a day; even if divided into longitudinal strips, instead of the sides turning in, as in the former case, each strip becomes inflated, and a tube is formed within it : and what is still more wonderful, and seems next to a miracle, these animals may be turned inside out, like the finger of a glove, without destroying either their vitality, their power of producing germes, and of catching, swallowing, or digesting

their food: so that they have, properly speaking, neither a within nor without, both surfaces of their alimentary canal being equally fitted for digestion. This, however, is not so entirely anomalous as it may at first sight appear; for cuttings of some vegetables, if planted inversely, will take root, the top bearing the root, and the bottom the branches and inflorescence.

The fresh-water polype usually remains fixed by its closed extremity to one spot, from which it seldom moves, exhibiting no other trace of an animated being than the motions of its arms; but when the want of light or heat causes it to shift its quarters, it moves slowly by fixing alternately, like a leech, its head and tail to what it is moving upon.

The majority of the marine polypes are attached, in some way, to a calcareous support formed by themselves, which is called by Amoureux, Lamarck, and other continental writers, their Polypary; and they are none of them locomotive except the last order.

4. The polypes of the second Order, the sheathed polypes of Lamarck, as the most important and interesting of this class of the animal kingdom, I wish to leave last upon the reader's memory. I shall, therefore, next make a few brief observations upon those sponges and alcyons

that have no tentacles, and form the fourth Order. These are included by Lamarck amongst those just mentioned, but they appear not properly to belong to them, and to have a still more simple organization. In this tribe, as was before observed, nutrition seems carried on by a kind of systole and diastole, the sea water being alternately absorbed and rejected by the tubes composing the substance of the sponge, they having no organs to collect their food in any other way.

Many of these productions are remarkable for being hollowed internally, and in their external shape resembling cups, bowls, and vases: several gigantic specimens of this kind were collected in India by the late lamented Sir Stamford Raffles, to whose indefatigable exertions, judicious arrangements, and uncommon ardour in her cause, science is so deeply indebted, and presented by him, with the rest of his valuable collections, to the Museum of the Zoological Society, where they are now to be seen. Their general structure also, as well as form, fits them for receiving a large quantity of water, as well as for parting with it, in proportion to the pressure, when received in the living animal, this pressure is produced by its expansion.

What particular function, or office, has been devolved by the All-wise Creator upon these zoophytes, which are produced so rapidly, and in such numbers, on the bed of the ocean and its

pur

rocks, has not been ascertained. As in the case of a vast variety of other marine animals, they probably derive their nutriment from the contents of the water absorbed by their tubes; they may contribute their part to the depuration of the oceanic waters, and to the maintenance of the equilibrium amongst their inhabitants, however minute, which is necessary to the general welfare. Doubtless, in their creation, He, who inhabiteth Eternity, to whose view all time as well as all space is present, had in view the benefit of his creature man, to whom they form a very useful present, and which he has long applied to his poses. Sponges were in use as early as Aristotle's time, when the people that employed themselves in collecting them observed, that when they attempted to pluck them up they appeared to resist, whence they concluded they had some sensation. They now form a very considerable article of commerce. The fishery for them is chiefly carried on in the Mediterranean, particularly in the Grecian Archipelago. The collection of them is attended with danger, as they are fixed to the rocks at the depth of several fathoms, so that the sponge-fishers must be excellent divers. Tournefort says, that no youth in these islands is allowed to marry, till he has given proofs of his capacity in this respect.

Aristot. Hist. Anim. B. i. c. 1, comp. B. v. c. 16.

Amongst plants, as Mr. W. S. Mac Leay has, I think, remarked, sponges present some analogy to the puff-balls.'

5. A fifth Order of polypes, worthy of attention, is that to which the red coral belongs, in these the animal instead of being covered, or in any way sheltered by its polypary, invests it completely, so as to form a kind of bark over every part of it; on this account the name has been changed by writers on these animals, and it is denominated their axis, since upon it they are, as it were, suspended, and run their prescribed race. This axis consists of a much more rigid, solid and lapidose substance, than the polypary of the really sheathed polypes, presenting when polished the smooth substance and lustre of marble, without any appearance of pores or other orifices when broken it exhibits the same kind of fracture as a stick of red sealing-wax; this description refers particularly to the red coral,2 for in some other genera belonging to the Order the axis is jointed,' and in others, very flexible.1 The sheathed corallines appear in some sort, to be analogues of those animals whose bodies are covered and defended by an external crust or shell, like the Testaceous Molluscans, the Crustaceans and the Insects; while the tribe in question,