550 Chas. W. Hargitt. 



and Ballowitz/ who has devoted attention chiefly to adults, giving 

 excellent figures of noteworthy variations, and includes also a 

 valuable review of literature. 



In view of these rather extended observations on the part of 

 European observers and the almost entire lack of similar study 

 of American medusae it has seemed to the writer for several years 

 that a comparison of Aurelia flavidula with Aurelia aurita might 

 afford valuable results. And with this in view the data presented 

 in the following pages have been worked out at such intervals 

 during the past three years as have been available. I regret very 

 much that a larger number of adult specimens have not been 

 available, the hope of securing which has delayed the final appear- 

 ance of the paper. It is believed, however, that sufficient data 

 are presented to show at least something of the extent and sig- 

 nificance of the variations. 



As already intimated, almost nothing along these lines has 

 been attempted in relation to American Scyphomedusae, while 

 the summary of observations by the present writer is all that has 

 been attempted on the Hydromedusae. L. Agassiz* has left a 

 few very brief and rather indefinite records of variation in Aurelia 

 flavidula. Concerning numerical variation he says: "These 

 variations in number arise from the interpolation of similar parts, 

 or from the abortion of some of them. I have observed on our 

 coast specimens with three, five, six and seven crescent-shaped 

 bodies, and the number of indentations along the margin increased 

 correspondingly. These deviations from the normal number are 

 rare with our species, and though Ehrenberg does not allude to 

 their frequency in the European, I should infer that they are more 

 frequent in Aurelia aurita than in Aurelia flavidula, for the simple 

 reason that malformations of the crescent-shaped bodies are rarely 

 met with in our species." 



As will be noted, there is apparent in these observations of 

 Agassiz, the same general assumption of a more or less close corre- 

 lation among the several organic systems of the medusae. I am 

 inclined to regard this as in some measure due to a temperamental 

 predisposition on the part of these earlier observers, perhaps 

 growing out of the peculiar ideas in reference to such matters 



^Archiv. f. Entwickelungsmechanik der Organismen, Bd. viii, S. 239. iS 

 ^Contr. Nat. Hist. U. S., 1862, vol. iv, p. 51. 



