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THE AMERICAN NATURALIST 



[Vol. L 



combination of the two patterns, called porima, occur under cer- 

 tain temperature conditions. The two patterns can not be Men- 

 delian allelomorphs of each other, though the possibility remains 

 they may have undiscovered allelomorphs. Too little is now 

 known of inheritance in this species for us to judge whether 

 Weismann's hypothesis in modern form is tenable, or whether a 

 single set of factors, or single factor, reacting differently to dif- 

 ferent environments, is sufficient to account for the two types. 



In a preliminary analysis of the problem the two color phases 

 seem like distinct ontogenetic stages. Levana possibly is prorsa 

 with immature colors, arrested in their development through the 

 action of cold. Prorsa in the chrysalis may pass rapidly through 

 the levana stage into its final, complete condition. Its offspring, 

 however, independently of the environment, hereditarily tend to 

 hibernate in the chrysalis and become levana. This interpreta- 

 tion of the two color phases is in line with the facts of dichro- 

 matism in beetles, as described by McCracken 6 and others. Gas- 

 irokUa (lissimilis, when it emerges from the pupal ease, is black, 

 and certain individuals permanently retain this color, others, 

 however, pass on to a permanent bright green phase. Lina lap- 

 ponica (Melosoma scripta) has a spotted-brown phase which is 

 either permanent or is replaced by black. The two color phases 

 in each of these forms, however, are Mendelian allelomorphs of 

 each other, the dominant color being that appearing first in ontog- 

 eny, the recessive last. 



The cold weather varieties of Colias eurytheme, about to be 

 discussed, certainly may be regarded as being produced in large 

 part by the arrested development of pigmentation. In this most 

 remarkable seasonally polymorphic butterfly of western and cen- 

 tral North America, Colias eurytheme, the writer has found that 

 the flaming orange coloration of the summer form (usually called 

 the typical eurytheme) and the paler orange-yellow of the spring 

 and autumn broods (ariadiu and kr< tvayelin) are variations also 

 due to differences in the reaction to the environment, of definite 

 Mendelian factors. This has been shown by crossing the orange 

 ( urythi me of the central and western states, with the clear yellow 

 species of the eastern and central states, Colias philoclice, the 

 yellow of which segregates cleanly from the orange in F 2 , as a 

 recessive. The hybrids, as well as the eurytheme stock, show 

 seasonal polymorphism. The F 1 hybrids, for example, are of a 



e Jour. Exper. Zool., 3, 1906. 



