COLOR AND COLORATION 183 



older, and more stable of the two forms, and the summer form a second- 

 ary, newer, and less stable variety ; since the latter form only, as a rule, 

 responds much to thermal influences. Weismann argued that, in addi- 

 tion to the direct effect of temperature, alternative inheritance also 

 plays an important part in the production of seasonal varieties. He 

 tried to show, moreover, that each seasonal variety is colored in adapta- 

 tion to its particular environment and that this adaptation may have 

 been brought about by natural selection though he did not succeed 

 in this respect. 



In several instances, local varieties have been artificially produced 

 as results of temperature control. Thus Standfuss produced in Ger- 

 many, by the application of cold, individuals of Vanessa urticce which 

 were indistinguishable from the northern variety polaris; and from 

 pupae 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. 



Shelf ord, by subjecting a pupa of a tiger beetle, C. tranquebarica 

 (vulgaris) to cold moist conditions (mean temperature, 12 C.; moist) 

 obtained, in Chicago, a color variety like one that occurs naturally in 

 the eastern mountains. 



In a second instance, both pattern and color were modified by hot 

 dry conditions (mean temperature, 37 C.; dry), and a variety obtained 

 such as occurs in the western states. 



In a third experiment, both pattern and color were modified by hot 

 wet conditions (37 C.; moist), and a variety produced like one in the 

 moist southern states. 



These investigators and others, notably Merrifield and Fischer, have 

 accumulated a considerable mass of experimental evidence, the inter- 

 pretation 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 

 inheritance of acquired characters. 



The seasonal increase in size that is noticeable, as in C. pseudargiolus 

 and /. ajax, is doubtless an expression of increasing 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 

 caterpillars were so much stimulated by unusual warmth that they 

 pupated before they were sufficiently fed, and gave, therefore, under- 

 sized imagines. A moderate degree of warmth, however, undoubtedly 

 hastens growth. 



