HYDROZOA. 119 



is proved alike by the existence of numerous tran- 

 sitional forms, and an appeal to the phenomena of 

 their development. 



3. That many other so-called Mednsidoe may, 

 from analogy, be regarded as, in like manner, me- 

 dusiform gonophores. 



4. But that there may exist, nevertheless, a 

 group of Medusid forms, which may give rise, by 

 true reprod action, to organisms directly resembling 

 their parents, and, therefore, worthy of being- 

 placed in a separate order under the name of Me- 

 dusidce. 



All the Trachynemidoe and ^ginidce belong, 

 according to Gregenbaur, to the order in question. 

 And to the same group may be referred, provision- 

 ally, that large assemblage of forms anatomically 

 similar to true Medusidce, but whose development 

 is unknown ; just in the same manner as genera 

 and species are established for those Diphyozooids 

 which, there is every reason to believe, are but 

 the detached fragments of other Calycophoridce. 

 Pending the study of the life-history of these am- 

 biguous Medusoids, their true nature must, also, 

 remain undetermined. 



Such are the forms brought together by Gregen- 

 baur in the systematic table here annexed, which, 

 at the same time, concisely displays their most 

 striking anatomical peculiarities. 



Order MEDUSID^ 



With radiating canals. 



Reproductive organs in the poly- 

 pite-wall. Ocelli at bases of the 

 tentacles . . . Family 1. Oceanidje. 



I 4 



