1 68 ENTOMOLOGY 



brood occurs marcia; in New York, the species is 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 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 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, 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, re- 

 sponds 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 colored 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. 



In several instances, local varieties have been artificially produced 

 as results of temperature control. Thus Standfuss produced in Germany, 

 by the application of cold, individuals of Vanessa urtica 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. 



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 /. ajaXj 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- 



