182 



ENTOMOLOGY 



varieties become successively larger, with longer tails to the hind 

 wings. 



Now Edwards submitted chrysalides of the summer form ajax to 

 cold and thereby obtained, in the same summer, butterflies with the 

 form of ajax but the markings of the spring form telamonides. Some of 

 the chrysalides, however, lasted over until the next spring and then gave 

 telamonides. 



In Phyciodes tharos (Fig. 236) 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 contrasting 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 



FIG. 236. Phyciodes tharos; A, spring form, marcia; B, summer form, morpheus; under 



surfaces. Natural size. 



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 distinctive coloration of the spring variety 

 is brought about by low temperature. In Labrador, only one brood 

 occurs marcia; in New York, the species if digoneutic (two-brooded) 

 and in West Virginia polygoneutic (several-brooded) . 



Extensive temperature experiments upon seasonal dimorphism in 

 Lepidoptera have been conducted in Europe by some of the most com- 

 petent biologists. Weismann found that pupae of the summer form of 

 Pieris napi, if placd 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 sum- 

 mer 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, 



