Variations Among Scyphomedusce. 551 



more or less prevalent at that time. Certain it is, that either 

 the more recent work on these lines have been more critical 

 and discriminating, or a remarkable change has taken place 

 since the earlier records v^ere made. Possibly something of 

 both may be true, though I incline to regard the former as more 

 probable. 



My investigations have been directed chiefly to two series of 

 facts, namely: Variations as exhibited in the ephyra, and those 

 found in the adult of Aurelia flavidula. Incidentally I shall 

 direct attention briefly to certain other species which have been 

 studied in connection with those of Aurelia, though of these no 

 details will be undertaken, since in ofily a few cases have sufficient 

 numbers been examined to warrant any general conclusions. 



Being strongly convinced of the general correctness of Haeckel's 

 view as to the relations of variations of the adult to similar con- 

 ditions found in the larva, or ephyra, it seemed desirable to secure 

 collections of specimens from various localities differing more or 

 less in physical conditions of environment in order to estimate the 

 probable influence of such conditions in relation to variation. 

 Accordingly I secured ephyra from three localities adjacent to 

 Woods Hole, in about equal numbers, approximately 500 from 

 each. (Unfortunately I was unable to obtain adults from the 

 same environments, since their locomotor powders, influence of 

 currents, winds, etc., carrying them every whither, made this quite 

 impracticable.) 



As is very well known, the Discomedusae are characterized in 

 general by the octamerous lobing of the umbrellar margin, cor- 

 related with which are eight rhopalia, or sensory bodies; and by 

 the tetramerous form of the stomach and oral arms. This is 

 more particularly the case with the semostomous group, to which 

 belong most of our larger medusae, of which Aurelia and Cyanea 

 are good examples. 



As will be seen, therefore, the organization of these medusae, 

 leaving out of account the tentacles, which difi^er greatly in the 

 several genera, presents two fairly differentiated and independent 

 sets of organs, namely, the marginal or sensory, and the central or 

 vegetative. In many cases these sets are correlated for nutritive 

 purposes through the radial canal system, though of themselves 

 they may for the present discussion be considered as independent 

 systems, distinctively organized and definitely correlated, as 



