106 ZOOPHYTES. 
II. Cycio-canetita or Motiusca. Cephalopoda, Pteropoda, Gas- 
teropoda, Conchifera, Tunicata. 
IIL. Dreto-NEuRA or ArticuLATA. Crustacea, Arachnida, Insecta, 
Myriapoda, Annelida, Rotifera, Entozoa. 
IV. Cycro-neura or Rapiata. Echinoderma, Acalephe, Polypi- 
phora (zoophytes), Poriphora (sponges), Polygastrica. 
An objection might be made to this system, on the ground of the 
apparent absence of nerves in some of the lower orders. But a real 
absence can hardly be concluded, from our inability to distinguish 
them. Many of these animals show by their voluntary motions and 
sensibility that nervous influences traverse the body: moreover, 
nervous matter is secreted only in lines. We can, therefore, only 
infer the indistinctness, and not the absence of nerves, from our in- 
effectual efforts to trace them out; and we must consequently be 
guided by general structure, in determining the relations of groups, 
when the nerves fail of giving aid. 
106. The above arrangement fails, in some respects, of presenting 
a clear idea of the system in nature, although highly philosophical in 
its general features. A study of the animal kingdom, as has been 
lately shown, brings to light, lines or general systems of developement 
branching up from the lowest infusoria to the higher grades of life. 
It is not true that the forms among the Jower grades are actually 
copied in any of the imperfectly developed young of the saperzor ; 
yet there is some general analogy, sufficient to indicate that the former 
commence on the same system of developement with some of the 
latter, although carried essentially out of the direct upward line by 
the peculiar vital forces of the species. The Rotifera are decidedly 
Crustacean in type. The stout mandibles are precisely those of some 
of the Cyclopide, even in position, and also in general form; and in 
certain peculiarities in the mode of reproduction, the animals are closely 
similar; yet no young Crustacean is ever a Rotifer. ‘The latter 
belongs to the same system of developement with the former, but 
is a distinct branch, from the regular line, characterized by peculiar 
natatory organs, which appear to be analogues of the branchial or 
basal appendages to the feet in Crustacea. ‘The Bryozoa,* or Flus- 
* The Bryozoa have been placed near the Rotifera ; but the absence of mandibles, as 
well as their peculiar type of structure, separates them widely from these crustaceoid 
species and allies them as closely to the Tunicata, with which they were first associated 
by Thomson, under the name of Polyzoa. Lister has a finely illustrated article on this 
subject, in the Philosophical Transactions, for 1834, p. 365. 
