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MANUAL OF ZOOLOGY. 



essential respects identical with those of the Corynida though 

 usually smaller. Each polypite consists of a soft, contractile, 

 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 is simple or lobed, and is 

 placed, in many cases, at the extremity of a more or less pro- 

 minent extensile and contractile proboscis. 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 coenosarc (fig. 24, b). The nutrient 



Fig. 24. a Sertularia (Diphasia) pinuata, natural size ; a' Fragment of the same 

 enlarged, carrying a male capsule (o), and showing the hydrothecse (k) ; b Fragment 

 of Campanularia neglecta (after Hincks), showing the polypites contained in their 

 hydrothecae (h), and also the point at which ;the coeuosarc communicates with the 

 stomach of the polypite (o}. 



particles 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 



