78 Inheritance of Melanism in Tephrosia (Ectropis) 



nomena observed in the last-named experiments were not those of 

 ordinary blending inheritance. Not only was there apparent dilution to 

 varying extents of a proved unit character, but in addition the fluctua- 

 tions obtained were so chaotic and irregular as to indicate the action of 

 some disturbing influence dislocating to a profound extent the mechanism 

 of Mendelian heredity as well as of that permitting a blend. In the 

 original set of experiments we were dealing with crosses between 

 different varieties of the same species, whereas in the latter the crossings 

 were interspecific ; for the inciting agents in the disturbance, therefore, 

 we have to look to circumstances arising out of the specific distinctness 

 of the insects used in the second series of experiments. 



Although not concerned with melanism, many other workers, when 

 working with species- and race-crosses, have met with irregularities 

 more or less parallel with mine. For instance, both Bonhote and the 

 two Hagedoorns, describing their hybridisation experiments with Mus 

 rattus, M. alexandrinus, and M. tectorum, mention rats (waltzers and 

 the like), departing widely from the normal, as appearing in their F2 

 cultures. Neither of these two investigators are prepared to grant that 

 their animals are mutants in the genetical sense of the word. Although 

 their views are possibly correct, for my part I feel sure that, no matter 

 how induced, their origin, as well as that of my aberrant moths, must 

 be assigned to causes precisely the same as those giving rise to mutations. 

 From this it seems hardly necessary to state that from their further 

 explanations I emphatically dissent. In the opinion of the Hagedoorns 

 we have to look to the joint action of two recessive^ characters whose 

 cooperation was impossible until the chance rearrangement of factors 

 brought about by segregation in F^ gametogenesis and their union in 

 the F2. zygotes ensured it. 



Bonhote, on the other hand, perceives the origin of the new characters 

 in a new environmental complex diminishing the initial vigour of the 

 animals he used. 



Not essentially different from these results, and perhaps not so 

 striking although more in harmony with mine, are those of Sumner, 

 who worked with local races of the Californian Deermouse (Peromyscus 

 maniculatus). In the F^. generation of hybrids between Peromyscus 

 maniculatus sonoriensis and P. maniculatus rubidus he obtained what 

 he terms " partial " albinos ; these he regards as almost certainly true 

 mutants, whose inception must be ascribed to the loss of a gene during 



1 I might agree with this if their "recessive" characters be regarded as equivalent to 



