CCELENTERATA : HYDROZOA. 



101 



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 are developed 

 in chitinous receptacles known as "gonothecag" (fig. 24, o). 

 The young Sertularian on escaping 

 from the ovum appears as a free-swim- 

 ming ciliated body, which soon loses its 

 cilia, fixes itself, and develops a young 

 coenosarc, by gemmation from which the 

 branching hydrosoma of the perfect 

 organism is produced. 



In Phimularia and some of its allies 

 there occur certain peculiar organs, 

 probably offensive, to which the name 

 of " nematophores " has been applied. 

 Each of these consists of a process of 

 the ccenosarc, which is invested by the 

 horny polypary, with the exception of 

 the distal extremity, which remains 

 uncovered, and contains many large Fi 

 thread-cells embedded in it. The 

 nematophores are sometimes fixed, 

 sometimes movable. They "constitute cup-like appendages, 

 formed of chitine, and filled with protoplasm, which has the 

 power of emitting pseudopodia or amoeboid prolongations of 

 its substance, and having their cavity in communication with 

 that of the common tube of the hydrocaulus " (Allman). 



ORDER IV. CAMPANULARIDA. The members of this order 

 are closely allied to the Sertuiarida so closely, indeed, that 

 they are very often united together into a single group. The 

 chief difference consists in the fact that the hydrothecae of the 

 Campanularida with their contained polypites are supported 

 upon conspicuous stalks, thus being terminal in position (fig. 

 24, b); whilst in the Sertuiarida they are sessile or subsessile, 

 and are placed laterally upon the branchlets. The gonophores 

 also in the Campanularida are usually detached as free-swim- 

 ming medusoids, whereas they remain permanently attached 

 in the Sertularians. Each medusoid consists of a little trans- 

 parent glassy bell, from the under surface of which there is 

 suspended a modified polypite, in the form of a "manubrium " 

 (fig. 21). The whole organism swims gaily through the water, 

 propelled by the contractions of the bell or disc (gonocalyx) ; 

 and no one would now suspect that it was in any way related 

 to the fixed plant-like zoophyte from which it was originally 



. 25. Ovarian capsule of 

 Diphasia (Sertularia) oper- 

 cu/a/a,~L'mn. (AfterHincks.) 

 Greatly enlarged. 



