Variations Ainong Scyphomedusce. ^^l 



more or less continuous from the earliest records of von Baer and 

 Ehrenberg to the present time precluding any probability of the 

 operation of simply incidental factors. 



An inspection of the tabulated records of more recent times will 

 show that the tendency has been constantly toward a more or less 

 definite increase of the several organs, particularly the marginal 

 or sensory, though' including also the central or vegetative. 

 If one had taken occasion to construct a curve representing the 

 various phases it would have shown that the variations had been 

 preponderatingly upon one side of the modal line. In the absence 

 of the curve it may facilitate a ready appreciation of the situation 

 to submit percentage values of the variations above and below 

 the normal. 



Results obtained by Browne covering a period of about five 

 years and including an examination of several thousands of speci- 

 mens presented in percentage figures are as follows: 



Normal. Above Normal. Below Normal. 



Rhopalia 78.71 per cent. 16.74 per cent. 4.55 per cent. 



Vegetative 97.6 per cent. 1.8 per cent. 0.6 per cent. 



Results obtained by my own observations covering a period of 

 four years and an examination of about 2500 specimens are as 

 follows : 



Normal. Above Normal. Below Normal. 



Rhopalia 75-07 per cent. 22.97 per cent. 1.96 per cent. 



Vegetative 97-24 per cent. 2.2 per cent. 0.56 per cent. 



The significance of this line of rather definite and continuous 

 variation is somewhat doubtful. Without specific details in the 

 work of Baer and Ehrenberg it is impossible to formulate con- 

 clusions as to the ratio of variation in Aurelia aurita as observed 

 by them, but the more recent observations of Bateson, Browne, 

 Ballowitz and those herein described, make it perfectly certain 

 that for at least two species of medusae from widely separated 

 regions variation has been remarkably active and continuous. 

 But at the same time it seems equally certain that so far as one 

 is able to see there has been no evidence of the operation of any- 

 thing like natural selection at work. The variant forms do not 

 appear to be more numerous than formerly, nor does the variation 

 seem to be appreciably larger in one species than in the other, if 



