No. 5.] VARIATION AMONG HYDROMEDUSAE. 247 



with Gonionemus all the facts would seem to point to their 

 independent origin, in many cases the tentacles being of con- 

 spicuously different sizes, and in others exhibiting all phases 

 of intermediate conditions between the simple bifurcation of 

 the terminal portion through the budding of a smaller tentacle 

 from the side of the larger, on to the symmetrical double ten- 

 tacles as shown in Figs. 3, 4, and 10. 



In only one case was a trifid tentacle found. This is 

 shown in PI. IV, Fig. 9. However, while a trifid structure 

 there seems to be a degeneration of the median lobe, which 

 was in all probability the terminal portion of what was origi- 

 nally a normal tentacle, from which later were budded the two 

 lateral shoots, each in turn becoming more prominent than the 

 median tip and developing in the appropriate places the charac- 

 teristic suctorial pads. The degenerating middle tip would 

 very naturally suggest the probability that an injury might 

 have been the predisposing cause of the secondary tips ; on the 

 other hand, it must not be overlooked that in each of the other 

 specimens with double tips no such cause seems at all evident. 

 I am inclined to consider the cases as simply the expression of 

 the intrinsic capabilities of variation, more or less evident in 

 the several classes of organs already considered. 



As yet no reference has been made to the order in which 

 second, third, and subsequent series of tentacles arise. Goni- 

 onemus, unlike Eucope, seems to have no such association of 

 tentacle and sensory bulb as serves to locate in part the pri- 

 mary set of tentacles and the order of appearance of the 

 subsequent series. While usually there is a single primary 

 tentacle at the terminus of each radial canal, this is not invari- 

 ably the case. An inspection of Figs. 9-12 will show that 

 there may be a very wide range of variation in this respect. 

 The following data, taken at random from many observations; 

 will further illustrate the same general fact. 



