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. Pupz derived from 
eges 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 pupz 
of the summer form of Picris napi, 1f 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 l’anessa 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. 
