DISCONTINUOUS VARIATIONS 



89 



is exceedingly strong. It is interesting further to notice that " the 

 newly-arisen species " is very successful as regards numbers, and 

 that its variations have a strong family resemblance to those of its 

 supposed ancestor, and are yet more abundant. In regard to its 

 more abnormal variants, Mayer observes that they are handicapped 

 by their loss of symmetry, for some are neither radial nor bilateral, 

 and by a reduction of fertility even in cases where the number of 

 gonads has been increased to six or seven. 



The evidence from Medusae and Medusoids is sufficient to show 



FIG. 21. Mutation in Medusoids (after A. G. Mayer). The figure to the 

 left is an oral view of Epenthesis folleata. The figure to the right is 

 an oral view of Pseudoclytia pentata. 



that discontinuous variations may occur in large numbers, that 

 similar brusque changes may occur year after year, that there is 

 sometimes a strong family resemblance in the variations of related 

 forms. In some cases (e.g. in regard to Aurelia aurita) we are not 

 in a position to say that anything has come of the abundant crop 

 of discontinuous variations ; in other cases (e.g. the very abnormal 

 forms of Pseudoclytia pentata} the discontinuity has gone too far, 

 as shown by the reduction of fertility and the entire loss of sym- 

 metry ; while, thirdly, from the relationship of Pseudoclytia pentata 

 to Epenthesis folleata, we are led to conclude that one species may 

 arise from the discontinuous variation of another. 



