404 RADIATA. 



ORDER II. GELATINOSI * 



THESE are distinguished from the preceding, by 

 a much greater simplicity of structure, as well as 

 by less firmness of texture ; consisting of nothing 

 more than a simple oblong bag of jelly-like flesh 

 without skin, furnished with a few tentacles around 

 the mouth. Some are placed upon a footstalk, and 

 are visible only with the microscope. The best known 

 genus is the fresh-water Polype, (Hydra,"^) several 

 species of which are abundant in our own country, in 

 stagnant pools and ditches. They consist of a delicate 

 transparent tube, from half an inch to an inch in 

 length when fully extended, attached at one end to 

 the stalks of water plants, by a little sucker, and fur- 

 nished at the other with from six to a dozen slender 

 tentacles, spread in form of a star around the mouth. 

 The substance of the body is somewhat like shagreen, 

 shewing a great number of little detached grains, of 

 a green colour in the commonest species, set in a clear 

 jelly, without skin, membranes, or vessels of any 

 kind. The tentacles are not usually longer than the 

 body, but in one species, the long-armed Hydra, (H. 

 Fusca,) they extend to the length of eight inches, but 

 of extreme slenderness, like a fine hair. The tenta- 



* Gelatinosus, jelly-like. 



t Named after the fabled monster of that name ; from its power of 

 reproducing parts cut off. 



