272 PSEUDACRAEA EURYTUS 



believes to be acted upon by Natural Selection, and 

 adduces proof that they can be inherited ! 



One can quite appreciate the argument that the theo- 

 retical origin of Euralia wahlbergi from a form of such 

 different appearance as mima would be an example of 

 origin by " Mutation " or *' Sport," but when it is neces- 

 sary to fine down the " largeness " as in the intermediate 

 fowls it becomes an apparent absurdity to allude to these 

 differences as " large," that is, as " sports." It seems 

 difficult to draw distinctions between the Mendelian's 

 " Mutation," which is inherited by segregation of some 

 very minutely differentiating " factor," and the Darwinian 

 " small " variation, which can be inherited, but which 

 the Mutationist calls a " fluctuation " and says is non- 

 heritable, but if proved to be heritable claims as a 

 "mutation" or "large variation." 



If segregation comes down to produce such minute 

 differences, the term " large variation, mutation or 

 sport " seems to be worn rather thin ! 



On this matter the work done by T. H. Morgan upon the 

 colour of the eye in the fruit fly Drosophila has a bearing. 

 The eye is normally red, but in the investigations upon 

 the inheritance of the eye colour it was found that there 

 were seven gradations between white and red, and further, 

 one of the grades has seven modifying factors, each of 

 which altera its intensity and gives rise to a secondary 

 grade. Professor Jennings remarks that " by means 

 of these graded changes one could obtain, by the 

 mutationist 's own statement, the continuously graded 

 results which selection actually gives. What more can 

 the selectionist ask ? " ^ 



A case strictly analogous to the case of Ps. eurytus, 

 with its abundance of insular variations in the absence 

 of the models, is noted by Professor Poulton in his presi- 



^ See a summary of Jennings' papers by Professor Poulton in the 

 Proceedings oj the Entomological Society oj London, 1917, pp. Ixxxv-lxxxix, 



