118 HTDROZOA. 



The reproductive organs have been stated to be 

 of the simplest kind, consisting of mere expansions, 

 either of the polypite wall, or radiating canals, 

 within which the generative elements are produced. 



At a time when the free gonophores of the 

 Hydrozoa had been as yet imperfectly studied, it 

 was the custom of naturalists to regard these bodies 

 as independent individuals, worthy of being ar- 

 ranged under definable genera and species. The 

 singular resemblance of such gonophores to the 

 MediisidcB began, at length, to attract attention. 

 Then it was suspected that many of the Mediisidce 

 were not individual organisms properly so called, 

 but merely the free reproductive buds of various 

 Hydrozoa. Eventually it was proposed to abolish 

 the whole group of Medusidce, and distribute their 

 several forms among the different orders of the 

 class. 



On the other hand, certain observations of J. 

 Miiller, Fritz jMliller, Gregenbaur, and Claparede, 

 to vv^hich we have already referred, indicate the 

 probable existence of a group of Medusid forms 

 which appear to be the immediate products of 

 true generative acts, not of gemmation or fission, 

 {fig- 12). 



In the present state of our knowledge, it seems 

 better to sum up the several aspects of this doubt- 

 ful question in the following series of conclusions. 



1. That several of the organisms formerly de- 

 scribed as Medusidce are the free gonophores of 

 other orders of Hydrozoa. 



2. That the homology of these free gonophores 

 with those simple expansions of the body-wall 

 which in Hydra and some other genera are known 

 "to be reproductive organs by their contents alone 



