CCELENTERATA : IIYDROZOA. 



91 



and extensile body, which is furnished at its distal extremity 

 with a mouth and a circlet of prehensile tentacles, richly fur- 

 nished with thread-cells. The tentacles have an indistinctly 

 alternate arrangement. The mouth opens into a chamber 

 which occupies the whole length of the polypite, and is to be 

 regarded as the combined body-cavity and digestive sac. At 

 its lower end this chamber opens by a constricted aperture 

 into a tubular cavity which is everywhere excavated in the 

 substance of the ccenosarc (fig. 17, b). The nutrient particles 



rig. 17. — a Sertularia {Dtpkasia) pinnaia, natural size.; a' Fragment of the same 

 enlarged, carrying a male capsiile {o\ and showing the hydrothecas {k) ; b Fragment 

 oi Camfanularia neglecia (after Hincks), showing the polypites contained in their 

 hydrothecae (Jt), and also the point at which the coenosarc communicates with the 

 stomach of the polypite (fi). 



obtained by each polypite thus serve for the support of the 

 whole colony, and are distributed throughout the entire 

 organism. The nutritive fluid prepared in the interior of each 

 polypite gains access through the above-mentioned aperture to 

 the cavity of the coenosarc, which by the combined exertions 

 of the whole assemblage of polypites thus becomes filled with 

 a granular nutritive liquid. This ccenosarcal fluid is in con- 

 stant movement, circulating through all parts of the colony, 

 and thus maintaining its vitality, the cause of the movement 

 being probably due, in part, at any rate, to the existence of 

 vibrating cilia. The generative buds (gonophores or ovarian 

 vesicles) are usually supported upon gonoblastidia, and seldom, 

 if ever, become detached in the true Sertularids. They are 



