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shell is more concave on one side than the other. The genus Spirula, the animal of which appears also to be a Cephalopod,1 seems to exhibit the first tendency to this form.
Amidst all this variety of Molluscous animals, exhibiting such diversity in their structure and organization, in their habits, food, modes of life, and stations, one great object seems attained by their creation especially, the production of calcareous matter. Even the shells of terrestrial testaceans, if we consider the vast numbers that every year perish, must add in no trifling degree to the quantity of that matter on the earth, and probably make up for the continual waste or employment of it, so as to maintain the necessary equilibrium; but in the ocean, the quantity added to that produced by corallines, must be exceedingly great, even in lakes beds are formed of the deposites 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 under-agents 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.
1 PLATE VII. Fio. 2.
Functions and Instincts.
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, enclosing 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 shows 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, 1 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 Infusoriesand 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 ani mal organization are to be found in its lowest grades. As I formerly observed with respect to the Infusories2-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 discription, 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.4 The Planaria, in some respects, partakes more of the nature of a polype than of any 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
1 See Zool. Journ. July-October, 1828, 260. 3 Hirudo.
5 Philos. Trans. 1825. i. 254. t. xvi. f. 10.
2 See above, p. 80.
4 Fasciola. Distoma.
polype. A farther 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 P. cornuta, is oviparous in the spring and gemmiparous in the autumn-observes that, in the latter season, it divides itself spontaneously and transversely into two parts above the abdominal orifice, and at the end of ten days, each of these parts has acquired the head or the tail that it wanted. He has divided individuals into many transverse pieces and two longitudinal ones, and every piece, in due time, completed itself. It formed eyes, an intestinal tube, and other
Mr. Dalyell and Dr. Johnson subsequently made similar observations, and by dividing the head had succeeded in producing an animal with two heads; the latter, from the result of several observations, found that each individual, upon an average, might, by spontaneous self-division, produce ten, and this when under constraint; if at liberty, and in their natural situation, we may conjecture that their reproductive powers might be carried much higher. Dr. Johnson divided one into three equal portions, when the head speedily acquired a new body and tail; the tail, a new body and head; and the middle piece a new head and tail.
From this whole statement it is evident that these pseudoleeches, to say the least, their substance considered, tend towards the polypes, and possess the same reviviscent powers. In several characters, which I shall notice hereafter, they also agree with the Annelidans. Draparnaud, from the approximation of the points on the head of P. cornula, to the tentacles of Lymnea, thinks that they form a link between the Mollus cans and the Worms. Reproductive powers have certainly been observed in the former, but only in the reproduction of mutilated organs, for a snail or slug cut in pieces, would not form so many individual animals. Bonnet has given an account of reproductive powers in one of the Hispid Worms, of Lamarck, supposed by Gmelin to be the Nais barbata of Müller, and in a species of fresh water worm belonging to the Annelidans, which, if I may so speak, grows from cuttings, and like the Planaria, can produce two heads. These last are probably not far removed from the flukes, though their station is so different. Whether they live on animal or vegetable matter is
1 Vers hispides.
not certainly ascertained; to look at their proboscis it seems rather calculated to fix them as suckers, to some animal, and so to derive their nutriment from it, like their analogue, the leech, especially as the marine species are supposed to be car
Their wonderful reproductive powers appear to be given them by a kind Providence to prevent their total annihilation; at least, it is stated, that at certain periods of the year, their numbers are so reduced, that where thousands were seen in summer, in spring scarcely one has survived. Their substance is so soft and gelatinous, that they are easily destroyed; to compensate this, they are gifted with the extraordinary powers of reproduction above described. God hath so tempered his sentient works, that seeming defects, in one respect, are compensated by redundance in another.
Having made these observations upon animals of this class, that do not infest man or beast internally, I next turn to those whose office is, in spite of all his care, to make the lord of the creation, as well as the whole animal kingdom, not only their constant abode, but also their food. More than twenty of these pestiferous creatures, that attack man, have been enumerated; some penetrate into the very seat of thought; others disturb his bile; others circulate with the blood in his veins ;3 others again, are seated in his kidneys; others in his muscles; the guinea worm in his cellular tissue: the ovaries of females are infested by another; the tape-worms extend themselves, joint by joint, to an enormous length in his intestines ; some select the large intestine; and others the small ones;10. some even attack infants, and them only." Such are the ills that flesh is heir to from these our internal assailants and devourers-The recital is really enough to cause our hair to stand on end. No one can believe that these instruments of punishment were at work in the first pair when they camefrom the hands of their Maker, and nothing except death, can prove with greater strength of evidence, that he is fallen from. his original state of integrity and favour with God, than such
1 Echinococcus Hominis.
3 Linguatula Venarum.
5 Hydatigera cellulosa.
7 Linguatula pinguicula.
8 Tania solium, and Botryocephalus Hominis.
9 Trichocephalus Hominis.
11 Oxyurus Vermicularis.
2 Fasciola hepatica.
4 Strongylus gigas.
6 Filaria medinensis.
10 Ascaris lumbricoides.