§ 70. 
of the hypotheses suggested in the above 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 
onlyin a somewhat transitionary state, in a zoological 
point of view.» Many genera which have hitherto 
been regarded good and permanent will no doubt, 
as Stebold has remarked, prove to be only unde- 
veloped forms of well-known species. As already 
atated, Agassiz regards the Hydroid Polypi as true 
Acalephae, and the analogy which exists between 
7 
THE ACALEPHAE. 
73 
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 have extensive and serial re~ 
searches in the embryology of these animals. For 
separate details on the development of some forms, 
see Busch, loc. cit. (Sarsia, Lizzia, Cephea, Eu~ 
doxia, Diphyes); Huxley, loc. cit. (Diphyidae, 
Physophoridae); Agassiz and Desor, loc. cit. 
(Medusidae). — Ep. 
