IITDROZOA. 95 



by the development from its opposite sides of 

 alternate leaflets, which eventually arch over, and 

 unite with one another, forming a basket-like 

 receptacle, or ' corbula,' within which the repro- 

 ductive bodies are lodged. 



In Sertularia pobjzonias and some other spe- 

 cies only one gonophore, consisting of a simple 

 closed sac, arises from the gonoblastidial column, 

 and, by the protrusion of this sac beyond the 

 orifice of the urn, an external capsule, or ' acro- 

 cyst,' is formed, into which the ova are trans- 

 ferred at a certain period of their development 

 {Jig. 19, e,/, and^). 



In Camioanularia Loveni the ripe gonoblas- 

 tidium displays at its summit the medusa-like 

 gonophores already alluded to, whose form is, in 

 many respects, so peculiar that Professor Allman 

 has proposed to designate them by a distinct 

 name, *meconidia' {Jig. 10). The reproductive 

 elements of this species are developed, as in the 

 Goi'ynidcv, between the ectoderm and endoderm 

 of the manubrial wall, while in other Sertularidce, 

 with medusa-like gonophores, they arise in the 

 course of the calycine canals. 



The order Sertidaridce includes two families. 



Order SERTULARID^. 



Family i. Sertulariad^. 



Hydrothecce, and polypit^s, sessile. 



Family 2. Campanulariad^. 



Hydrothecoe, and polypites, stalked. 



A more extended acquaintance with the posi- 

 tion of the nematophores may perhaps afford 

 grounds for modifying this arrangement. 



