HYDROZOA. 45 



is in Hydractinia. 



3. That of a manubrium with closed gonocaly- 



2. That of a well-defined process, or sporosac, as 



cine investment, in which case the medusoid 



- •; 



^ structure is said to be "disguised," as in the 

 1 - gonophores of Cordylophora and numerous other 



b forms. 



anUl 4. That of a manubrium, with open gonocalyx 



*v he. and well-developed canal system. Such " medusi- 



/• 8, form gonophores" may either remain attached, 



•"d car as in Hippopodius and Vogtia, or become free, 



bu as in Velella, Porpita, and many of the fixed 



r dot Hydrozoa. 

 1 t ] The same gonophore does not contain more 



( / than one kind of generative elements, and these 



, ,^.. are situated either between the ectodermal and 



[er „ . endodermal layers of the manubrium, or in the 



1 • walls of the gonocalycine canals. When male and 



r ^ female gonophores differ externally in form, the 



■■ special terms < androphore ' and € gynophore ' are 



1 su ~ such sexual distinctions, two kinds of gonophores 



appear occasionally to be produced by the same 

 Hydrozoon, while, on the other hand, similar 

 negoi gonophores may arise from the bodies of appa- 

 _ ..;... rently different species. 



So much, then, for the structure of the gono- 

 in i phores ; next, as to their position. They may be 

 seated either — 



ient \ 1 . on the polypites ; or, 



* mem't 2 - on # special processes termed * gonoblas- 



tidia;' or, 



]j bodf 3 ' directl y on the coenosarc. 



tD • The first of these methods is characteristic of 



employed to distinguish them. But, apart from 





