56 INVERTEBRATE ANIMALS. 



cleavage from a primitive organism. It does not matter, 

 therefore, for the purposes of this definition, whether these 

 beings remain permanently attached to the original organism, 

 or whether they are finally separated to enjoy an independent 

 existence. 



Hydrosoma (Gr. liudra, a water-serpent; soma, body). 

 The term " hydrosoma " is one which is very conveniently ap- 

 plied to the entire organism in any Hydrozoon, whether this 

 be simple, or whether it be composite and made up of a num- 

 ber of connected zoOids. 



Potypite. That portion of any Hydrozoon which is con- 

 cerned with the process of digestion, or, in other words, the 

 "alimentary region," is termed the "polypite" the more 

 generally current term of " polype " being now restricted in 

 meaning to the same region in the higher Coelenterata (Ac- 

 finozoa). In such of the Hydrozoa as the fresh-water polype 

 or Hydra, in which the hydrosoma is simple, the whole or- 

 ganism is termed a polypite ; but the term is more generally 

 employed to indicate the nutritive zooids of any compound 

 Hydrozoon. 



Ccenosarc. The term " coenosarc " (Gr. Jcoinos, common ; 

 sarx, flesh) is employed to designate the common trunk or 

 flesh by which the separate polypites of any compound Hy- 

 drozoon are united into a single organic whole. 



Polypary. The term " polypary " or " polypidom " is ap- 

 plied to the horny or chitinous outer covering or envelope 

 with which many of the Hydrozoa are furnished. These terms 

 have also been not uncommonly employed to designate the 

 very similar structures produced by the much more highly or- 

 ganized sea-mats and their allies (Polyzoa), but it is better to 

 restrict their use entirely to the Hydrozoa. 



