No. 5-] VARIATION AMONG HYDROMEDUSAE. 239 



of the last type, a fact, when taken in connection with the 

 closely similar number of distinctly pentamerous forms, of 

 great importance as showing that in neither case are we war- 

 ranted in concluding that the course of variation is in one 

 direction rather than in another. In order to reach anything 

 approximating conclusiveness on this point a larger number of 

 specimens studied through a successive series of years would 

 be necessary. As I have already intimated, the collections 

 forming the basis of the present discussion of this genus were 

 made during at least four years, and while I have not made 

 this a matter of critical comparison, it has not been at all 

 apparent that during this period there has been any appreci- 

 able ratio of difference. 



Passing now to the consideration of other aspects of varia- 

 tion evident in the canals, attention is next directed to their 

 morphology. As is well known, the chymiferous canals in 

 medusae are tubular structures of fairly constant size in 

 members of the same species and of similar sizes, and their 

 courses are usually direct from the center to the margin in 

 most of the Hydromedusae. As Agassiz and Woodworth 

 ('96) have shown in the case of Eucope, however, there are 

 not a few departures from this rule. The same is true of 

 Gonionemus, as a glance at Pis. I and II will demonstrate. Not 

 only does the diameter of the canal vary greatly in many speci- 

 mens, which is of only incidental concern, but in many cases, 

 as in PI. I, Figs. 9, 1 1, and 12, various loops and diverticula in 

 the form of spurs are formed at various points and at various 

 angles along their course. These are of varying sizes, lengths, 

 etc., and were found on between one and two per cent of all 

 the specimens examined. In the paper just cited the authors 

 suggest in these facts a possible simulation of a condition 

 "characteristic of the Discophores " (p. 122). Whether there 

 is in these structures anything more than simulation or paral- 

 lelism as compared with the Scyphomedusae, I shall not at 

 present discuss. 1 As compared with the typical canal, however, 



1 It may not be amiss, however, to state in this connection that in Rhegma- 

 todes there is a much more evident correspondence or resemblance in this matter 

 than in either Gonionemus or Eucope. While possessing a large number of 



