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THE AMERICAN NATURALIST [Vol.XLVI; 



spot. The mutation proved to be an ordinary Mendelian reces- 

 sive. This spot is absent normally in curtula, and in crosses 

 between anachorcta and curtula it 'does not appear in F u or at 

 least is never of the full size. Its behavior in this hybrid is 



quired in order to explain it. But Federley's assumption of 

 imperfect dominance of the same gene which behaves as a com- 

 plete dominant in the anachorcta mutant seems hardly justifi- 

 able. The fact that the character behaves in the mutant as 

 though due to a single factor does not mean that it must al- 

 ways so behave. It may depend upon the simultaneous pres- 

 ence or absence of several genes. If in the "spotless" mutant 

 one of the required genes has dropped out, then the addition of 

 that one to the complex will give the spot, and a ease of Men- 

 delian monohybridism will result. But curtula may be "spot- 

 less" because it lacks some other part of the required combina- 

 tion, in which case the behavior might be quite different from 

 that in the case of the mutant. 



When curtula and pigra were crossed, some of the F t imagos 

 erged after a pupal stage of about two weeks, while the rest 



hibernated 



noths resulting 



were quite different, the first (summer generation) being more 

 similar to curtula, the second (spring generation) more like 

 pigra. That this difference is not due to the effects of temper- 

 ature is indicated by an F, moth reared from eggs laid by an 

 individual of the summer generation. This moth hibernated 

 in the pupal stage, yet resembled the summer generation. Fur- 

 hybrids and upon curt ula-anachor eta hybrids gave entirely neg- 

 ative results. Several facts bearing on this problem are given. 

 Seasonal dimorphism is never a well-marked phenomenon in 



Pygcera, and does i 



the three species 



dealt with by Federley. From pigra he was unable 

 summer generation. In the case of curtula. the Finnish races 

 are univoltine, the German ones usually bivoltine. Crosses 

 between the two latter did not give any consistent results. 



The cross between anachorcta female and curtula male gives 

 an F, brood which is sexually dimorphic. The males resemble 

 th <*»" omvhonta mothers, and the females resemble the curtula 

 1 Vrom the reciprocal cross only males were reared. These 

 also resembled anachorcta. However, Standfuss reared both 



