3s 



THE AMERICAN NATURALIST 



[Vol. LII 



in late larval stages. This production is therefore 

 stopped when female metabolism sets in; when then the 

 time arrives in development, when the chromogen spreads 

 over the wing scales, its available amount is proportional 

 to the relative lateness of the reversal of sex. Therefore, 

 with increasing inter sexuality, the pigment flowing from 

 the veins covers a smaller and smaller area of the wing, 

 finally being confined to the neighborhood of the veins. 

 As 2 the analysis of the other intersexual organs allows 

 an accurate determination of the time factor involved, we 

 have here a very close physiological parallel to the facts 

 about the caterpillars. 



In most other cases of multiple allelomorphism only 

 the results can be seen, and it will be difficult to work out 

 the time factor, which proves that the multiple allelo- 

 morphs are different quantities of an active substance. 

 (Some botanical subjects ought, however, to be favor- 

 able.) But in comparing the other facts about multiple 

 allelomorphs with our cases, we feel confident that, where- 

 ever a similar analysis can be applied, the results will be 

 the same. For example, all the cases of quantitatively 

 different pigmentation, which are of multiple allelo- 

 morphic nature, like Castle's hooded rats or our different 

 cases of melanism in moths, show* that the effect of the 

 different factors is that different quantities of pigment 

 spread from different "points of outlet," which of course 

 are hereditary traits of the species or group ; the similar 

 effect, therefore, leads to suspect a similar cause. 



If our conclusions regarding the nature of multiple 

 allelomorphs are accepted, it must lead to a different intel- 

 lectual attitude toward the problem of variability of 

 genes, which is so important for evolution. The opposi- 

 tion to the view has been, we believe, primarily on aprio- 

 ristic grounds. In the long controversies of recent years 

 regarding the interpretation of Castle's work the logical 

 side of the case seems to have always been in the fore- 

 ground. The same is the case when E. Baur calls our 



2 See pictures in Jour. Exp. Zool., 22, 1917, pp. 614-15. 



