CCELENTERATA : SERTULARIDA. 



12.3 



distinctly alternate arrangement. The mouth is simple or 

 lobed, and is placed, in many cases, at the extremity of a more 

 or less prominent 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 every- 

 where excavated in the substance of the ccenosarc (fig. 46, b}. 

 The nutrient particles obtained by each polypite thus serve for 

 the support of the whole colony, and are distributed through- 

 out the entire organism. The nutritive fluid prepared in the 

 interior of each polypite gains access through the above-men- 

 tioned aperture to the cavity of the ccenosarc, which by the 

 combined exertions of the whole assemblage of polypites thus 

 becomes filled with a granular nutritive liquid. The ccenosar- 

 cal fluid is in constant 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 do not become detached in the true Sertularids. They 



A 



Fig. 47. Diagrams of the gonothecae, with their con- Fig. 48. Ovarian cap- 



tents, of the Sertularians and Campanularians. sule of Diphasia (Ser- 



Chitinous envelope ; g Central gonoblastidion or tularia) operculata, 



blastostyle ; e Medusiform gonophores carried upon Linn, (after Hincks). 



the blastostyle, each with a central manubrium, in Greatly enlarged, 



the walls of which the generative elements are pro- 

 duced ; s Sporosacs carried upon the blastostyle, 

 each with a central pillar (spadix), round which the 

 ova are developed. (Altered from Allman.) 



are developed in chitinous receptacles known as "gonothecae " 

 (figs. 47, 48). 



