86 



MANUAL OF ZOOLOGY. 



single whitish polypite, striped with pink, and terminating 

 upwards in a pear-shaped head, round the thickest part of 

 which is a circlet of from forty to fifty long white tentacles. 

 Above these comes a series of long branching gonoblastidia, 

 bearing gonophores, and succeeded by a second shorter set of 

 tentacles which surround the mouth. The gonophores become 

 ultimately detached as free-swimming medusoids. 



ORDER III. SERTULARIDA (Thecaphora, Hincks). This order 

 comprises those Hydrozoa " whose hydroscma is fixed by a hy- 

 drorhiza, and consists of several polypites, protected by hydrothecce, 

 and connected by a ccenosarc, which is usually branched and in- 

 vested by a very firm outer layer. Reproductive organs in the 

 form of gonophores arising from the ccenosarc or from gonoblas- 

 tidiar (Greene.) 



The Sertularida resemble the Corynida in becoming" perma- 

 nently fixed after their embryonic condition by a hydrorhiza, 

 which is developed from the proximal end of the ccenosarc ; 

 but they differ in the fact that the polypites are invariably pro- 

 tected by "hydrothecae," or little cup-like expansions of the 

 polypary (fig. 17, a, b) ; whilst the hydrosoma is in all cases 



Fig. 17. a Sertularia (Dtphasid) pinnata, natural size ; a' Fragment of the same 

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

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

 hydrothecse (ft), and also the point at which the ccenosarc communicates with the 

 stomach of the polypite (o). 



composed of more than a single polypite. The ccenosarc 

 generally consists of a main stem or "hydrocaulus" with 



