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MANUAL OF ZOOLOGY. 



primitive body-cavity of the non-ciliated embryo is ultimately 

 placed in communication with the outer world by the forma- 

 tion of the mouth, which is produced directly as an opening in 

 the walls of the body, and not by invagination of the ectoderm. 



ORDER II. CORYNIDA (Gymnoblastica, Allman ; Athecata, 

 Hincks). The order Corynida comprises those Hydrozoa 

 whose hydrosoma is fixed by a hydrorhiza, and consists either of 

 a single polypite, or of several united by a ccenosarc, which usually 

 develops a firm outer layer or " polypary." No " hydrothecee" 

 are present. " The reproductive organs are in the form of gono- 

 phores, which vary much in structure, and arise from the sides of 

 the polypites,from the ccenosarc, or from gonoblastidia " (Greene). 



The hydrosoma of the Corynida may consist of a single 

 polypite, as in Coryomorpha and Vorticlava, or it may be com- 

 posed of several united by a ccenosarc, as in Cordylophora 

 (fig. 39, a). The order is entirely confined to the sea, with 

 the single exception of Cordylophora, which inhabits fresh water. 

 In Tubularia and its allies the organism is protected by a well- 

 developed external chitinous envelope or " polypary ; " but in 

 the other genera belonging to the order, the polypary is either 



Fig. 39. Morphology of Corynida. a Fragment of Cordylophora lacustris, slightly 

 enlarged ; b Fragment of the same considerably enlarged, showing a polypite and 

 three gonophores in different stages of growth, the largest containing ova ; c Portion 

 . of Syncoryne Sarsii with medusiform zooids budding from between the tentacles. 



rudimentary or is entirely absent. The polypary of the 

 Corynida, when present, is readily distinguished from that of 

 the Sertularida, by the fact that in the former it extends only 

 to the bases of the polypites ; whereas in the latter it expands 

 to form little cups for the reception of the polypites, these cups 

 being called " hydrothecae." Owing to the fact that neither 

 the polypites nor the generative buds of the Corynida are en- 



