204 ENTOMOLOGY 



In Phyciodes tharos (Fig. 233) the spring and summer 

 broods, termed respectively marcia and morpheus, were at first 

 regarded as distinct species. In marcia the hind wings are 

 heavily and diffusely marked beneath with -strongly contrast- 

 ing colors, while in morpheus they are plain and but faintly 

 marked. Edwards placed upon ice eighteen chrysalides that 

 normally would have produced morpheus; but instead of this, 

 the fifteen imagines that emerged were all of the spring form 

 marcia and were smaller than usual. Pupae derived from 

 eggs of marcia gave, after artificial cooling, not morpheus, 

 but marcia again. The evident conclusion is that the distinc- 

 tive coloration of the spring variety is brought about by low 

 temperature. In Labrador, only one brood occurs marcia; 

 in New York, the species is digoneutic (two-brooded) and in 

 West Virginia polygoneutic (several-brooded). 



Extensive temperature experiments upon seasonal dimor- 

 phism in Lepidoptera have been conducted in Europe by some 

 of the most competent biologists. Weismann found that pupae 

 of the summer form of Pieris napi, if placed on ice, disclosed 

 the darker winter form, usually in the same season, though 

 sometimes not until the next spring. It was found impossible, 

 however, to change the winter variety into the summer one 

 by the application of heat. Similar results have attended the 

 important and much-discussed experiments of Dorfmeister, 

 Weismann and others upon Vanessa levana-prorsa and other 

 species, from which it has been inferred by Weismann that 

 the winter form is the primary, older, and more stable of the 

 two forms, and the summer form a secondary, newer, and less 

 stable variety; since the latter form only, as a rule, responds 

 much to thermal influences. Weismann argues that, in addition 

 to the direct effect of temperature, alternative inheritance also 

 plays an important part in the production of seasonal varieties. 

 He tries to show, moreover, that each seasonal variety is col- 

 ored in adaptation to its particular environment and that this 

 adaptation may have been brought about by natural selection 

 though he does not succeed in this respect. 



