HTDROZOA. 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 jpolyzonias 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 

 {fig. 19, e,/, and^r). 



In Campanularia 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' {fig. 10). The reproductive 

 elements of this species are developed, as in the 

 Corynidce, 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 SertularidcE includes two families. 



Order SEKTULARID^. 



Family i. Sertulariad^. 



Hydrothecce, and polypites, sessile. 



Family 2. Campanulariad/E. 



Hydrothecce, and polypites, stalked. 



A more extended acquaintance with the posi- 

 tion of the nematophores may perhaps afford 

 grounds for modifying this arrangement. 



