Variations Among Scyphornedusce. 575 



serve to suggest the fact that the species varies greatly, but chiefly 

 in the nonessentials of color and size, the southern forms being 

 usually much smaller than those of more northern range. 



In structural features I have found that this species exhibits 

 very similar variations to those found in Aurelia. While it has 

 not been w^ithin the scope of the present paper to enter upon any 

 large survey of the problem as it relates to Cyanea, and no exact 

 data have been accumulated, I have examined considerable 

 numbers of both the ephyrae and adults, and find considerable 

 variation in the number of rhopalia, the gastric and oral lobes, 

 and the less important matter of coloration to which reference 

 has been made above. 



Similar observations have also been made upon our species of 

 Dactylometra, and to the same eff"ect. In general aspects it 

 varies less than does Cyanea, as perhaps both vary less than does 

 Aurelia, but concerning the fact of considerable variation there 

 can be no doubt. In a paper upon the structure and development 

 of Dactylometra, Mayer* has stated that the tertiary tentacles 

 arise invariably on either side of the ocular lappets. While I have 

 had no opportunity to examine any considerable number of these 

 medusae, I have nevertheless, found considerable disparity on 

 this point. In several specimens examined in 1902 I found these 

 tentacles arising at points intermediate between the primary and 

 secondary series. 



I have also found considerable variation in the number of the 

 rhopalia and other marginal organs. Since, however, the data 

 are too few to warrant any definite attempt at estimating the quan- 

 titative variations of either of these species, it must suffice merely 

 to note the facts in a qualitative way and leave to another time, 

 or other observer, the further consideration of details. 



RHIZOSTOMA PULMO. 



Among about fifty specimens of this medusa which I had 

 occasion to examine critically in the progress of experiments upon 

 regeneration, an account of which has been published elsewhere, 

 and perhaps half as many others examined in the large aquaria 

 less critically, about 15 per cent showed features of variation in 



Bull. Mus. Comp. Zool., vol. sxzii. 



