HYDKOZOA. 29 



zoon the entire somatic cavity may be said to 

 perform the functions of a nutritive apparatus 

 {Jig. 5, 6). But the true digestive process is 

 chiefly effected within the bodies of the poly- 

 pites. 



Each polypite exhibits two regions, a distal, and 

 a proximal. The distal extremity terminates in a 

 delicate, more or less extensile, lip, which, in 

 the Calycophoridce and Physophoridce, becomes 

 everted and trumpet-shaped. Not unfrequently, 

 the lip is lobed, its lobes, usually four in number, 

 being, in some cases, very much prolonged (fig. 

 7. b). 



In Hydra, and a few of the simpler forms of 

 Coin/nidcB, the proximal end of the poljrpite is 

 closed by the hydrorhiza, but throughout the re- 

 mainder of the class, it freely opens into the 

 somatic cavity. 



jNIauy CcdycojyJwridce and Fhysophoridce have 

 the proximal or attached division of the polypite 

 produced into a more or less elongated peduncle, 

 beyond which may be recognised two distinct re- 

 gions ; a median, or gastric, and a distal, or oral. 

 The gastric cavity is separated from the interior of 

 the proximal region by a peculiar inward growth, 

 or * pyloric valve,' which is best seen among the 

 Calycophoridce. Professor Huxley, its discoverer, 

 describes it as "a strong circular fold of endoderm, 

 whose lips, when the valve is shut, project into 

 the cavity of the gastric, or median, division of 

 the polypite. As the oily or albuminous globules 

 which result from the digestive process are formed, 

 they usually accumulate close to the valve, and 

 are kept constantly rotating by the cilia which 

 line the gastric chamber. After remaining for 



