Ca th ir: 
GENERAL STRUCTURE OF ZOOPHYTES. 
3. THE term zoophyte is applied to the whole animal structure, 
whether a single animal, or consisting of a large number of animals, 
as in most corals; while the several individuals are called polyps. 
In view of their general radiated structure,—the arrangement of 
the tentacles around a disk as a centre, and a corresponding circular 
structure within,*—these animals are placed in the Fourth grand 
division of the Animal Kingdom—the Rapiara. The distinguishing 
characteristics of the simple polyp, are as follows: 
An inarticulate fleshy body, nearly cylindrical, having a circular or 
eluptical summit called the disk, bordered by one or more series of ten- 
tacles, and an opening or mouth at the centre of the disk ; internally, a 
visceral cavity closed below, no distinct vascular system, an imperfect 
nervous system or none, and no senses but those of taste and touch. ‘The 
body, and, in most instances, the tentacles also are expanded by means 
of water, which is ejected on contraction. 
Polyps are thus among the simplest of animals, being even less 
complex in structure than the minuter Rotifers. A simple visceral 
cavity, and a single opening to it placed at the centre above, with 
traces of a radiated structure around it, are the only essential points ; 
for even the tentacles are sometimes wanting. ‘They have no intes- 
tine, no glands to aid in digestion, separate from the general walls of 
the internal cavity,—no system of vessels in any part for circulation, 
—an imperfect nervous system, if any,—no distinction of sex,—and no 
senses but those of taste and touch, with the latter of which the former 
may properly be included. Moreover they are mostly dependent on 
the fluid in which they live for the means of expanding their tenta- 
* Some of these animals are represented in figures 1, 6, and 12 beyond, and numerous 
species are given in the Atlas. 
