COLOR AND COLORATION 2OI 



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, 

 widespread among the higher animals, are little understood,, 

 but appear to be due chiefly to temperature. 



Albinism is exceptional whiteness or paleness of coloration,, 

 and is due usually to lack or deficiency of pigment, but in 

 some instances (Pieridse) to the presence of a white pigment. 



The common yellow butterfly, Colias philodice, and its rela- 

 tives, are frequently albinic. Indeed, as Scudder observes,, 

 albinism among butterflies in America appears to be confined 

 to a few Pieridae, and to be restricted to the female sex; it is 

 more common in subarctic and subalpine regions than in lower 

 latitudes and altitudes, and only in the former places does it 

 include all the females. At low altitudes, instead of appear- 

 ing early in the year as might be expected, the albinic forms 

 appear during the warmer months. 



In Europe there are many albinic species of butterflies, and 

 they are by no means Confined to the family Pieridse. 



Melanism is unusual blackness or darkness of coloration. 

 As to how it is produced little is known, though warmth is 

 probably the most potent influence, and some attribute it to 

 moisture, as was mentioned. Pictet obtained partial melan- 

 ism in Vanessa urticce and V. polychloros by subjecting the 

 larvae to moisture. 



In warm latitudes, some females of our Papilio glaucus 

 are blackish brown with black markings, instead of being, as 

 usual, yellow with black markings. In the South, some males 

 of the spring brood of Cyan-iris pseudargiolns are partly or 

 wholly brown instead of blue. 



Seasonal Coloration. When butterflies have more than 

 one brood in a year, the broods usually differ in aspect, some- 

 times so much that their specific identity is revealed only 

 by rearing one brood from another. The same species may 

 exist under two or more distinct forms during the same sea- 



