must be exceedingly great, even in lakes beds are formed of the deposits of the shell-fish inhabiting them, how much more gigantic must they be in the ocean, this will be evident from the superior number and size of the oceanic shells compared with the minute species, the Limnea, Planorbis, &c. that inhabit our lakes and pools. Thus, as reefs and islands are formed by the coral animals, the bed of the ocean may be elevated by the shells of dead testaceous ones. That eye which is never closed, that thought which is never intermitted, that power which never rests, but, engaged in incessant action, and employing infinite hosts of underagents to effect his purposes, sees and provides for the wants of the whole creation: the plant absorbs from the soil, the animal after devouring the plant, or the plant-fed creature, returns to the earth what the plant had absorbed, and so maintains the proper equilibrium ; He who numbers the hairs of our head, numbers the workmen that he employs, employing them only in such proportions so distributed, as may best accomplish His purposes. We are now at length, after long wanderings, arrived, if I may so speak, at the limits of the Molluscan territory, and, having visited the capital, seem now to be upon the confines of the higher hemisphere of the animal kingdom, the inhabitants of which are distinguished by having their whole frame built upon a vertebral column, inclosing a medullary chord, and terminating, at its upper extremity, in a skull containing a developed brain. But though we seem arrived at the confines of this higher order of animals, there are still many, and some superior to the most perfect of the Molluscans, in the entirety of their nervous system, and the habits and instincts which they manifest, to which we have not yet paid the attention that they merit. These animals are particularly distinguished from the preceding Classes, by the appearance, or actual existence of segments or joints in their bodies, especially in their legs, of what may be called an annular structure. They are divided into two great tribes, which, from this circumstance, have been called Annelidans, and Annulosans, and the last, with more propriety, Condylopes. There is one tribe, however, amongst the Radiaries, as we have seen, that shews some slight traces of insection, I allude to the star-fish and sea-urchins, forming the main body of Lamarck's Order of Echinoderms. If we examine the former, we find them marked out into areas, and in the latter, as I have before stated at large, the whole shell consists of numerous pieces united by different kinds of sutures. Before I call the reader's attention to the two tribes lately mentioned, exhibiting the appearance or reality of insection, I must notice an anomalous tribe of animals, whose real station has not been satisfactorily made out. I am speaking of the Entozoa or Intestinal Worms. This Class, as Mr. W. S. Mac Leay has remarked, consists of animals differing widely in their organization, some having a regular nervous system formed by a medullary collar sending forth two threads, while others have no distinct organs of sense. Lamarck places this Class between the Tunicaries and Insects, and Cuvier, amongst his Zoophytes, between the Gelatines and Echinoderms. Mr. Mac Leay has divided it into two classes, placing one, consisting of the Parenchymatous intestinal worms of Cuvier, between the Infusories and Polypes, and the Cavitaries of that author, amongst the Annulosans or Condylopes. Dr. Von Baer is of opinion that these Entozoa, or worms, reducible to no common type of organization, inhabiting various animals in various parts of their body, together with the Infusories and others might be added-should be banished from a natural arrangement of animals. He seems also to think, in which I feel disposed to agree with him, that the leading types of animal organization are to be found in its lowest grades.' As I formerly observed with respect to the Infusories-these appear to be the basis on which God has built the animal kingdom. As some of the species appear connected with the Annelidans, I have introduced the Class here, but not as having formed any settled opinion as to its proper division and legitimate station. The majority of this Class are, what their name imparts, intestinal worms, or parasites, that have their station within the body of other animals. Some of them, however, do not answer this description, as they are found only amongst aquatic vegetables; of this kind is a little tribe, which Linné arranged with the leeches, to which they approach by the flukes. The Planaria, in some respects, partakes more of the nature of a polype than of any 3 1 See Zool. Journ. July-October, 1828, 260. 2 See above, p. 148. 4 Fasciola. Distoma. other animal. Draparnaud, who paid particular attention to them, says that when young they have only two eyes, and acquire two more when adult. The head has no mouth; beyond the middle of the body, and on its under side, is a single orifice which serves for mouth, anus, and nostrils. This orifice answers to a long sac, which is the intestinal tube; from it sometimes issues a white tubular organ, which he regards as respiratory; this organ is doubtless the same with the retractile trumpet-shaped proboscis, issuing from a circular aperture in the middle of the abdomen, mentioned by Dr. Johnson in his interesting paper on these animals in the Philosophical Transactions, which he supposes to be a kind of mouth, when extended, equalling in length the animal itself. This remarkable organ was also noticed by Müller and Mr. Dalyell. The circumstance of its receiving and extruding its aliment and respiring at the same orifice, is a clear approximation to the polype. A further confirmation of this is the power this animal possesses of spontaneously dividing itself for the purpose of reproduction. M. Draparnaud-after remarking that the species he described, which he calls P. tentaculata, and which is probably synonymous with that particularly noticed by Dr. Johnson under the name of 1 Philos. Trans. 1825. i. 254. t. xvi. f. 10. VOL. I. Y |