No. 5.] VARIATION AMONu HYDROMEDUSAE. 



231 



whether additional sets of tentacles, etc., would be found 

 correlated therewith. 



The origin and symmetrical interpolation of such secondary 

 canals is very different, it seems to me, from that arising from 

 the bifurcation seen in Eucope and Gonionemus, though their 

 function in the economy of the organism may be the same. 



Only one phenomenon more will be discussed in this con- 

 nection, namely, that of double or twin medusae, which is 

 shown in Fig. 7. Only one specimen of this character was 

 found in the entire lot. In every respect --size, general form, 

 organic relations, etc., the 

 double feature alone ex- 

 cepted --the specimen 

 seemed fairly normal, hav- 

 ing this one further feature, 

 that one was a tri- 

 merous specimen 

 and that one set of 

 tentacles contained 

 three as against the 

 two each of the other sets. The furrow : like depression along 

 the line of union presents the aspects of late coalescence 

 similar to that involved in artificial grafting (cf. Biological 

 Bulletin, Vol. I, p. 41). 



But a more critical examination shows that the union is 

 much more profound, involving the gastric cavity and there- 

 fore the whole chymiferous system. 



The specimen was not seen alive, and hence nothing can 

 be said as to coordination of physiological activities, mode of 

 progression, etc. But from what has been proved from ex- 

 perimentation on these points (cf. op. cit.} it may safely be 

 inferred that similar coordination at least prevailed in such a 

 case as that under consideration. 



FIG. 7. 



Podocoryne. 



Of medusae of this genus I have had at my command only 

 a few more than one hundred specimens, a number too small 



