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THE AMERICAN NATURALIST [Vol. XLVIII 



strictly a matter of inheritance. Its " fluctuation " is not 

 due to a difference in environmental conditions surround- 

 ing different individuals, but evidently to the condition of 

 the germ plasm. The parents of any brood may be 

 heterozygous or homozygous for the determiners of color 

 pattern. If they come from a strain homozygous in this 

 respect and are alike in appearance, the offspring will 

 resemble the parents closely and show a narrow range of 

 variation, but if unlike and derived each from unlike 

 parents, a wide range of inherited "fluctuation" occurs. 

 Such is often the case in the inheritance of a melanic 

 tendency so often attributed to the action of the environ- 

 ment, and of spots used in the diagnosis of species as, for 

 example, the conspicuous spot in the middle of the under 

 side of the hind wing. This is commonly double in Colias 

 philodice and C. eurytheme, consisting of a chief and an 

 accessory spot, single in C. palceno, an arctic ciroumpolar 

 species, but it varies enormously. In eurytheme and 

 philodice the accessory spot may be absent; in palceno, in 

 rare cases, it may be present. I have bred large families 

 of C. eurytheme in which both the chief and accessory 

 spots were, like those of the parents, almost uniformly 

 large and nearly equal in size. In other families, from 

 parents in which the accessory spot is nearly or quite 

 lacking, the offspring show a similar reduction. In 

 C. philodice I have found it possible by selection to estab- 

 lish a race devoid of the row of submarginal red-brown 

 spots of the under side of the wings. Thus, by selection, 

 strains, nearly or perhaps quite homozygous for definite 

 points of color pattern, may be established, derived from 

 a population which in the main is in an extremely hetero- 

 zygous condition. Yet species are named and distin- 

 guished on the basis of these features. 



Another example of heterozygous condition of a char- 

 acter within a wild species is the white pigment in the 

 ground color of the " albino " female of Colias, both in 

 the yellow species, philodice and the orange species, 

 eurytheme. The white female is regularly heterozygous 



