'^ 70. 



THE ACALEPHAE. 



7a 



of the hypotheses suggested in the abore note. 

 Hitherto there has been much confusion on this 

 subject, from the want of complete series of obser- 

 vations ; even now the whole class can be regarded 

 • only in a somewhat transitionary state, in a zoological 

 point of view. Many genera which have hitherto 

 been regarded good and permanent will no doubt, 

 as Siebold has remarked, prove to be only unde- 

 veloped forms of well-known species. As already 

 stated, Agassiz regards the Hydroid Polypi as true 

 AcaJephae, and the analogy which exists between 



the embryos of Medusae and Polypi may be the 

 foundation of many other important changes. At 

 present, however, broad generalizations must be 

 deferred until we hare extensive and serial re- 

 searches in the embryology of these animals. For 

 separate details on the development of some forma, 

 see Busch, loo. cit. (Sarsia, Lizzia, Cephea, £u- 

 doxia, Diphyes) ; Huxley, loc. cit. (Diphyidae, 

 Physophoridae) ; Agassiz and Desor, loc. cit. 

 (Medusidae). — £9. 



