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COLOR AND COLORATION 179 



cases, however, the possible influence of low temperature and other 

 factors must be taken into consideration. The experiments of Merrifield 

 and of Standfuss showed no effect of moisture upon lepidopterous pupae. 



Pictet has found, however, that humidity acting on the caterpillars 

 of Vanessa urtica and V. polychloros has a conspicuous effect on the 

 coloration of the butterflies. Thus when the caterpillars were fed for 

 ten days with moist leaves, the resulting butterflies had abnormal 

 black markings on the wings, and the same results followed when the 

 larvae were kept in an atmosphere saturated with moisture. 



Climatal Coloration. The brilliant and varied colors of tropical 

 insects are popularly ascribed to intense heat, light and moisture; and 

 the dull monotonous colors of arctic insects, similarly to the surrounding 

 cliniatal conditions Climate undoubtedly exerts a strong influence 

 upon coloration, but the precise nature of this influence is obscure and will 

 remain so until more is known about the effects separately produced by 

 each of the several factors that go to make up what is called climate. 



The prevalence of intense and varied colors among tropical insects 

 is doubtless somewhat exaggerated, for the reason that the highly 

 colored species naturally attract the eye to the exclusion of the less 

 conspicuous forms. Indeed, Wallace assures us that, although tropi- 

 cal insects present some of the most gorgeous colors in the whole realm 

 of nature, there are thousands of tropical species that are as dull colored 

 as any of the temperate regions. Carabidae, in fact, attain their greatest 

 brilliancy in the temperate zone, according to Wallace, though butter- 

 flies certainly show a larger proportion of vivid and varied colors in the 

 tropics. Mayer finds, in the widely distributed genus Papilio, that 200 

 South American species display but 36 colors, while 22 North American 

 species show 17. While the number of species in South America is 

 nine times as great as in North America, the number of colors displayed 

 is only a little more than twice as great; hence Mayer concludes that 

 the richer display of colors in the tropics may be due to the far greater 

 number of species, which gives a better opportunity for color sports to 

 arise; and not to any direct influence of the climate. Furthermore, the 

 number of broods which occur in a year is much greater in the tropics 

 than in the temperate zones, so that the tropical species must possess a 

 correspondingly greater opportunity to vary. 



Albinism and Melanism. These interesting phenomena, wide- 

 spread among the higher animals, have often been attributed to tempera- 

 ture, but albinism and melanism are, in some instances at least, 

 strongly inherited without regard to temperature. 



