296 TOILERS IN THE SEA. 



is no real opening through which the polype passes. 

 It is the upward movement of the tentacular crown 

 which carries with it, and everts, the flexible sheath, 

 and so permits the imprisoned zooid a certain amount 

 of communication with the outer 

 world ; but the cavity of the cell 

 itself is sealed. The movements 

 of the polype, in the acts of expan- 

 sion and retraction, are limited to 

 the eversion and inversion of the 

 sheath ; and only the crown is 

 brought into immediate contact 

 with the surrounding water " 1 

 (fig. 58). 



There is nothing which calls 

 for special notice, or description, 

 here of the stomach and its diges- 

 tion, of the nervous or muscular 

 system, and other minute ana- 

 FIG. 58. tomical details, which would be 



POLYZOA essential for the student, but 



(Paludicella). 



rather let us seek to learn some- 

 thing of the " brown bodies " as they are called, which 

 have been the cause of considerable controversy. 

 Let us take, for example, one of the erect growing 



1 "History of the British Marine Polyzoa," by Thomas 

 Hincks, London, 1880, vol. i. p. 17. 



