16 ZOOPHYTES. 
10. General Divisions of Zoophytes. Zoophytes constitute natu- 
rally two distinct groups, differing in mode of reproduction and in 
internal structure. ‘The visceral cavity in some of them is, as de- 
scribed, a simple tubular sac. In others, it is divided vertically by 
fleshy lamelle, proceeding from the walls and forming a radiate series 
around the cavity. Connected with these peculiarities, we observe 
striking differences in the mode of ejecting the ovules. When there 
are lamelle in the cavity, the ovules are formed by them, and appear 
in clusters attached to the margin, from which they are finally de- 
tached, and make their escape out of the mouth. But when there 
are no lamelle, the ovules are produced in the walls of the visceral 
cavity, and make their readiest escape outward through the sides of 
the polyp, instead of the more indirect route, into the visceral cavity 
and out of the mouth. 
The following are the divisions based on the characters mentioned :* 
OrpER HypbRoIpea. 
Visceral cavity, a simple tubular sac; reproductive functions re- 
siding only in the walls of the cavity; young or ovules pullulating 
from the sides of the parent. 
OrpDER ACTINOIDEA. 
Visceral cavity, divided vertically by fleshy lamelle, which possess 
reproductive functions; ovules formed within the cavity from some of 
the lamelle and ejected through the mouth. 
The polyps of the order Hyproipga are mostly minute, and the 
coralla, when any are formed, are either horny or membranous; they 
are very delicate, and, when compound, usually consist of minute 
caliclest (or little cups), arranged in series along a tubular axis. 
tentacles are furnished with vibratile cilia. Excepting their calcareous secretions and 
mode of budding, they are widely removed from true zoophytes. (Sce farther §§ 106-8.) 
The definition also excludes sponges, as already intimated, which, excepting the most 
general attribute of animal matter (if they are animals), possess nothing in common with 
the polyp. No single character, except their forms, has ever been pointed out which 
indicates a relationship. 
* The names below have the following derivations :—Hydroidea is from the included 
genus LHydra, and Actinoidea from the included genus Actinia. This last name (from 
ax, ray of the sun,) alludes to the radiated character of the animals. 
} The term cadicle (from caliculus, a little cup,) is used for the prominences which con- 
tain the cells in many corals ; and ce// is restricted to the cavity itself. By ceddude, as here- 
afier used, the minute pores of the corallum will be referred to. 
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