COLOR AND COLORATION 201 
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 (Pieridee) 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 Pieride, 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 Pieridz. 
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 urtice and V. polychloros by subjecting the 
larvee 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 Cyaniris pseudargiolus are partly or 
wholly brown instead of blue. 
Seasonal Coloration.—\Vhen 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- 
