te pees) 
Zoology. ~ 
~ also in general form; and in their mode of reproduction, the animals 
are closely similar; yet no young crustacean is ever a Rotifer. The 
latter belongs to the same system of development with the former, but 
js a distinct branch, from the regular line, characterized by the peculiar 
natatory organs, which appear to be the analogues of the branchial or 
basal appendages to the feet in Crustacea. The same reasoning ap- 
plies to the Bryozoa or Flustroid polyps, which are as nearly allied to 
the Tunicata as the Rotifers to Crustacea.* It is a side-development 
from the imaginary line, which connects the Infusoria with the tuni- 
cated molluscs. ‘The Entozoa afford other examples, one branch of 
them passing into the Crustacea through the Lerneide and Caligide, 
and another into the Annelida. 
These remarks are intended to support no monad or Lamarckian 
theory, but only to elucidate the established principle that there are in 
nature certain distinct systems or types of development. Each species 
is developed with some reference to one or the other of these systems, 
but, through the agency of the vital forces peculiar to itself—forces 
which there is reason to believe only creative power can change. 
In accordance with these principles, the several orders of animals 
may be arranged as follows : 
I. VERTEBRATA. 
Il. Arricunata. II. Motiusca. 
Insecta, Myriapoda, Cephalopoda, Pteropoda, 
Arachnida, |G , Conchifera, 
Crustacea, Annelida. hee Cer Tunicata. 
Rotifera, Entozoa. adie ie Bryozoa. 
Zoophyta, Acalephe. 
V. Protozoa or Infusoria. 
A radiated structure characterizes in general the simplest forms of 
animal life. Passing up from the monad globule, this structure has its 
highest development in the Echinoderms. Among Zoophytes, the 
Hydra forms the first step upward, in which the digestive cavity is a 
mere sac, which will work equally well inside out, and the mode of 
reproduction is extremely simple. From this group we pass to the Ac- 
tinia, in which there is a distinct stomach and a series of fleshy lamelle 
around the internal cavity—the first rudiments of an insolation of the 
* The Bryozoa have been placed near the Rotifera ; but the absence of man- 
dibles, as well as their peculiar type of structure, se es 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 
vag illustrated article on this subject in the Philosophical Transactions for 1834, 
p- 365. 
