POLYPI. 869 
author had placed in a division of his Echinodermata. The animals of this 
class are either fixed by a base, or float freely in the ocean, and many are 
suspended in the water by the specific lightness of some of their parts, or 
by the air contained in their bodies. Their substance is gelatinous, without 
apparent fibres, though susceptible of contraction and dilatation. The sort 
of vessels, found in some, are merely canals in the gelatinous substance, 
connected with the stomach; none of their movements seem connected with 
muscular action ; there is no proper cavity for containing organs; the moutn 
or the suckers, or tentacula in the centre of the inferior surface is unpro- 
vided with hard parts; and the stomach, or the organ of digestion, and 
nutrition, is a simple sac without outlet. Between this sac and the external 
is a complicated but obscure organization. The Acalepha shine during the 
night with a luminosity. Many species are ornamented with lively colors. 
They are common in all seas. Cuvier divides the class into two orders, viz. 
1. Those where the body is fixed by a base either permanently or occasion- 
ally; and 2. Those which float freely in the ocean. 
CLASS XIII.—POLYPI. 
Gelatinous animals with elongated, contractile body, and an alimentary sac with 
one opening ; mouth distinct and terminal, surrounded with tentacula or radi- 
ated lobes ; the greater number adhering together, and forming compound 
animals. 
Tue class of Polypi or Zoophytes, is one of the largest and most singular 
of the Animal Kingdom. 
Nearly at the lowest step in the animal scale, many of them have the 
form of plants, accompanied by the simplest organization of parts for a liv- 
ing being capable of reproduction. Destitute of head and eyes, and having no 
organs for circulation, respiration or locomotion, the body of the Polypus ap- 
pears only asa homogeneous substance, constituted of gelatinous and irritable 
cellular tissue, in which the fluids essential to life move sluggishly. Allare, 
however, furnished with an internal cavity or stomach, with faint traces in 
some of hollow canals and ovaries. The body is generally cylindrical or 
conical, gelatinous or transparent; and the mouth surrounded by tentacula, 
varying in number and form, serves also for arms. Many of the polypi have 
the principle of life so diffused in their structure, that portions cut from the 
individual soon acquire, in the proper element, all the characters of the per- 
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