400 JOHN H. GEROULD 



On the other hand, Federley ('20) has recently analyzed the 

 case of supposed mutative effects of cold in Fischer's ('01) experi- 

 ments with Arctia caja, and shown that the supposed positive 

 results that have often been quoted as proof of the inheritance 

 of acquired characters are in all probability due to the heterozy- 

 gous nature of the stock. 



I concur entirely with his conclusion that wild species fre- 

 quently are only apparently constant, but really heterozygous 

 for a considerable number of genes, and have emphasized this 

 in an essay (Gerould, '14) calling the attention of systematists 

 to the importance of testing species whenever possible by inbreed- 

 ing and cross-breeding them. Federley, furthermore, makes 

 the interesting suggestion that ' varieties' are groups of individ- 

 uals showing rare combinations of genes (extracted recessives 

 from the heterozygous type), while 'aberrations' are still rarer 

 combinations from complexes of polymeric factors. 



ACTION OF ENVIRONMENTAL FACTORS AND GENES UPON CERTAIN 



BLOOD PIGMENTS 



There can be little doubt that the blood plasma plays an 

 important part in the ontogenetic development of seasonal 

 variations, which in some cases are as strikingly abrupt as muta- 

 tions. An interesting example of this class of variations has 

 recently come to the attention of the writer. Two forms of 

 Leptalis spio, a pierid butterfly, occur in Porto Rico, specimens 

 of the generation emerging in May being marked with orange, 

 those of the July brood with yellow,^ the latter but not the 

 former being an excellent 'mimic' of Heliconius charitonius. 

 It would be interesting to discover the relation of pigments in 

 the hemolymph to this striking change. Climatic changes in 

 radiant energy and moisture produce periodically and rhythmi- 

 cally in cases like this a reversible chemical reaction in blood 

 pigments involving a visibly abrupt variation. The seasonal 

 difference may be said to be 'quaUtative,' though it is brought 

 about by a quantitative difference in temperature or moisture. 



5 To Mr. F. E. Watson, of the American Museum of Natural History, I am 

 indebted for the idea and the evidence that this is a case of seasonal dimorphism. 



