go MANUAL OF ZOOLOGY. 



Each tube is filled with a soft, semi-fluid, reddish coenosarc, 

 and gives exit at its distal extremity to a single polypite. The 

 polypites are bright red in colour, and are not retractile within 

 their tubes, the horny polypary extending only to their bases. 

 The polypites are somewhat conical in shape, the mouth being 

 placed at the apex of the cone, and they are furnished with 

 two sets of tentacles. One set consists of numerous short 

 tentacles placed directly round the mouth ; the other is com- 

 posed of from thirty to forty tentacles of much greater length, 

 arising from the polypite about its middle or near the base. 

 Near the insertion of these tentacles the generative buds are 

 produced at proper seasons. 



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 oP 

 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 by 

 a hydrorhiza, and consists of several polypites, protected by hydro- 

 thecce, and connected by a ccenosarc, which is usually branched and 

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

 form of gonophores arising from the cxnosarc or from gonoblas- 

 tidia" — (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 coenosarc ; 

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

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

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

 composed of more than a single polypite. The coenosarc 

 generally consists of a main stem — or " hydrocaulus"- — with 

 many branches ; and it is so plant-like in appearance that the 

 common Sertularians are almost always mistaken for sea-weeds 

 by visitors at the seaside. It is invested by a strong corneous 

 or chitinous covering, often termed the " periderm." 



The polypites are sessile or subsessile, hydra-form, and in all 

 essential respects identical with those of the Corynida, though 

 usually smaller. Each polypite consists of a soft, contractile. 



