COLOR AND COLORATION 205 
In several instances, local varieties have been artificially pro- 
duced as results of temperature control. Thus Standfuss 
produced in Germany, by the application of cold, individuals 
of Vanessa urtice which were indistinguishable from the 
northern variety polaris; and from pupe of Vanessa cardui, 
by warmth, a very pale form like that found in the tropics; 
and, by cold, a dark variety similar to one found in Lapland. 
These investigators and others, notably Merrifield and 
Fischer, have accumulated a considerable mass of experimen- 
tal evidence, the interpretation of which is in many respects 
difficult, involving as it does, not merely the direct effect of 
temperature upon the organism, but also deep questions of 
heredity, including reversion, individual variation, and the in- 
heritance of acquired characters. 
The seasonal increase in size that is noticeable, as in C. 
pseudargiolus and I. ajax, is doubtless an expression ®f in- 
creasing metabolism due to increasing temperature. Warmth, 
as is well known, stimulates growth, and cold has a dwarfing 
effect. While this is true as a rule, there are some apparent 
exceptions, however. Thus Standfuss found that some cater- 
pillars were so much stimulated by unusual warmth that they 
pupated before they were sufficiently fed, and gave, therefore, 
undersized imagines. A moderate degree of warmth, how- 
ever, undoubtedly hastens growth. 
Sexual Coloration.—The sexes are often distinguished by 
colorational as well as structural differences. Colorational 
antigeny (this word signifying secondary sexual differences 
of whatever sort) is most prevalent among butterflies, in 
which it is the extreme phase of that differentiation of orna- 
mentation for which Lepidoptera are unrivaled. 
The male of Pieris protodice (Fig. 234) has a few brown 
spots on the front wings; the female is checkered with brown 
on both wings. In Colias philodice (Fig. 235) and C. eury- 
theme the marginal black band of the front wings is sharp 
and uninterrupted in the male, but diffuse and interrupted by 
yellow spots in the female. In the genus Papilio the sexes 
