76 



MANUAL OF ZOOLOGY. 



tolerably deep water, may be taken as a good example of the 

 fixed and composite division of the order. The hydrosoma 

 consists of numerous polypites, united by a ccenosarc, which 

 is more or less branched, and is defended by a horny tubular 

 polypary. The polypites are borne at the ends of the branches 

 and branchlets, and are not contained in ' hydrothecEe,' the 

 polypary ending abruptly afc their bases. The polypites are 

 non- retractile, of a reddish colour, and provided with about 

 twenty tentacles, arranged round the mouth iu a single 

 row (fig. 15). Tubularia. is very similar to Eudendriuwi, 

 but the hydrosoma is either undivided or is very slightly 

 branched. 



Coryomorpha nutans may be taken to represent those Cory- 

 nida in which there is no polypary and the hydrosoma is 

 simple. It is about four inches in length, and is fixed by 

 filamentous roots to the sand at the bottom of the sea. It 

 consists of a 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 hydrosoma is fixed Ity a hydro- 



rhiza, and consists of several 

 polypites, protected by hy- 

 drothecce, and connected by 

 a co3nosarc, which is usu- 

 ally branched and invested 

 by a very firm outer layer. 

 Reproductive organs in the 

 form of gonophores arising 

 from the cosnosarc or from 

 gonoblastidia.' (Greene.) 

 The Sertularida resem- 

 ble the Corynida in beco- 

 ming permanently fixed 

 after their embryonic con- 

 dition by a hydrorhiza, 

 which is developed from 

 the proximal end of the 

 coenosarc ; but they differ 

 in the fact that the poly- 

 hydro thecae/ or little cup- 



Fig. IG.SerMaHa rosacea,the lily-coralline, 

 showing ovarian vesicles. 



pites are invariably protected by 



