POLYPI. 869 



author had placed in a divisioa of his Echinodermaia . 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 mouth 

 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. — POL YPI. 



Gelatinous animals tvith elongated, contractile body, and an alimentary sac with 

 one opening ; mouth distinct and terminal, surrounded ivilh tentacula or radi- 

 ated lobes ; the greater number adhering together, and forming compound 

 animals. 



The 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 as a homogeneous substance, constituted of gelatinous and irritable 

 cellular tissue, in which the fluids essential to life move sluggishly. All are, 

 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 difi'used in their structure, that portions cut from the 

 individual soon acquire, in the proper element, all the characters of the per- 



73* 



