46 HTDROZOA. 



the Calycophoridw, the second of the PhysopTio- 

 ridoe and Sertidaridce, while all three find acces- 

 sible representatives in the order Corynidce. 



In certain species of this last order the gono- 

 phores, even on the same individual, obey different 

 modes of attachment. Thus in Clava midticornis^ 

 some are inserted on the polypites, others on gono- 

 blastidia ; while in Hydractinia, besides the gono- 

 phores borne on the gonoblastidia, a few are found 

 to arise, without intervening support, from the 

 sides of the coenosarc. 



The gonoblastidia are either simple or branched. 

 Often they present a curious resemblance to true 

 polypites, from which, however, they differ in 

 wanting a mouth, and having usually shorter ten- 

 tacula. Such polypoid gonoblastidia may be ex- 

 amined with ease in Hydractinia, where they are 

 less than the polypites in size. In this genus the 

 free extremity of each is seen to end in a pear- 

 shaped, tapering enlargement, whose surface is 

 studded with minute conical swellings containing 

 thread-cells, which increase in size so as to re- 

 semble rude tentacles, ten or twelve in number, 

 around the largest portion of the pyriform pro- 

 cess. Beneath these the gonophores are borne. 

 At the base of the process is inserted a proble- 

 matical body, presenting the appearance of a short 

 stalk, which terminates distally in a rounded ex- 

 pansion, filled with very small, dark orange, masses 

 of pigment. 



In general, gonoblastidia arise from the sides of 

 the coenosarc, though, in some cases, they are 

 attached to the bodies of the polypites. 



A curious structural modification distinguishes 

 the gonoblastidia of the Sertidaridce, In Gam- 



