582 Chas. W. Hargitt. 



indeed we really have in Aurelia aurita and Aurelia flavidula 

 definitely distinct species, a query which has frequently forced 

 itself upon my attention during the present research. 



In this connection has naturally arisen the question as to the 

 operation of any process akin to mutation. Mayer^ in a recent 

 paper on "The Variations of a Newly Arisen Species of Medusa," 

 p. 4, reviewing the variations in Aurelia remarks: "It is evident 

 that symmetrical "sports," or discontinuous variations of Aurelia, 

 are continually being produced, and yet the form of the species 

 as a whole remains unchanged." 



I have previously discussed the matter of the syynmctry of these 

 variations, and need not take it up again, further than to say that 

 it seems to me unfortunate to contend for the dominance of the 

 idea of symmetry in the sense referred to, and that so far as it 

 appears to me there is little in these variations which can be 

 regarded as "discontinuous," or mutative. They seem on the 

 contrary to be definitely continuous, and somewhat of the nature 

 of fluctuating variations. Browne's suggestion {op. cit., p. 100), 

 that "if a very slow and gradual change is taking place in the 

 number of tentaculocysts, then the tendency is toward the estab- 

 lishment of a race with ten tentaculocysts, due to an increase of 

 two opposite perradial tentaculocysts," hardly seems warranted 

 from the facts as known. I can hardly see that there is any such 

 predetermined variation as would be called for by his suggestion. 



So far as I am aware, the only case of variation among medusae 

 which might seem to be of the nature of mutation is that of 

 Pseudoclytia pentata, Mayer (op. cit.). Of this case we have 

 only the records of a single series of observations. Whether sub- 

 sequent evidence will clearly confirm Mayer's conclusions remains 

 to be seen. Furthermore, the results would have to be followed 

 through several generations of medusae in order to clearly estab- 

 lish the case as one of definite mutation, and this the future must 

 determine. 



'Mayer: The Variations of a Newly Arisen Species of Medusa. Bull. Mus. Brooldyn Inst. Arts 

 and Sciences, vol. i, 1901, 



