Notes on some'Hydromedusae from the Bay of Naples. 567 



riation in matteis of cleavage, particularly amoug- liydroids, and 

 Conn's contention is not tlierefore, valid as an objection. 



The researches of Brauer, however, leave little doubt tliat on 

 this point CiAMiciAN was evidently mistakeu, and my own obser- 

 vatious tend to confirm this conclusion. Brauer maintains that clea- 

 vage in this species takes place by two sharply dififerent processes, 

 namely, first, by a more or less regulär mode of fairly equal clea- 

 vages diiring the two meridional furrows, later oues being more or 

 less unequal and irregulär. In the second mode cleavage involves 

 the nuclei only, which proliferate independent of the cytoplasm, 

 forming a multinucleate egg, after which there follows a cleavage 

 of the egg into as many cells as there are nuclei. In this process 

 there may be considerable variety. It may occur when there are 

 bat few nuclei, four or six, or it may not begin until there are 

 sixteen, or perhaps more. 



My own observatious upon this point, while confirming in a 

 measure those of Brauer, do not warrant any such sharp conclusion 

 as to the distinctness of these processes. One may find a regulär 

 cleavage into two and four cells, etc., and he may also find an 

 internal nuclear proliferatlon, in some cases indeed, many more 

 nuclei arising than Bkauer has indicated, before cell Organization 

 and cleavage take place. But I have not been able to sharply 

 diÖerentiate these modes. They often graduate imperceptibly into 

 each other, indeed, may be found occurring in the same egg, though 

 this is not common. I am inclined therefore, to consider them as 

 only varying phases of cleavage conditions more or less common 

 among Coelenterates, particularly among Hydromedusae. This is 

 notably the case with Pennaria, as I have recently shown, and as 

 Allen (op. cit.) has shown in the case of Tiibidaria crocea. 



As illustrating somewhat more clearly than is possible by 

 merely verbal description I have included a few Sketches made by 

 Miss HowLANi) in connection with a study of sections already re- 

 ferred to. 



In Fig. 9 is shown an egg in which nuclear proliferatlon is 

 under way, but in which no signs of cleavage are present. This 

 condition may continue somewhat indefinitely, as already suggested, 

 tili finally a syncytium is formed, very much as in the case of 

 Pennaria (op. cit.), and as shown in Fig. 11, from which by a gra- 

 duated process of cell Organization and differentiation the gemi layers 

 are finally established, as shown in a latev paragraph. 



