18 BRITISH HYDROID ZOOPHYTES. 



A bell with a clapper will serve as an illustra- 

 tion. The clapper representing the polypite 

 with the mouth at the free end, the bell 

 corresponding exactly to 'he large expansion of 

 the base. Sometimes there is a thin 

 membrane partly closing the mouth of the bell 

 called the " veil." 



Radiating canals. Opening out of the 

 base of the stomach and traversing the bell 

 radially, like the ribs of an umbrella, are four 

 or more channels which extend to the margin 

 of the bell and unite by running along it ; this 

 canal system serves to convey nutriment from 

 the stomach to parts of the bell. 



Channels, the homologue of ten- 

 tacles. It has been conclusively shown that 

 these radiating canals represent the polypital 

 tentacles* which are formed after the same 

 manner as the buds, viz. : by the simple process 

 of inflation, thus producing long, tubular 

 processes, which, in most polypites are closed, 

 but in some are open. 



The bud, therefore, in progressing through 

 the water, strongly contracts the bell, and 

 thereby expels the water, the re-action 



*See Clavatella, Hincks' Brit. Hyd. Zoophytes, p. 70, et seq. 



