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THE AMERICAN NATURALIST [Vol. XLV 



17| homozygous white, ww, + 35^ heterozygous white, 

 w(o), +17| homozygous orange, 00, = 53| white [ww 

 + w(o)] +17^ orange, which accords closely with the 

 actual count, viz., 52 white (helice), 19 orange {edusa). 



3. GENERAL OBSERVATIONS ON THE GENUS ColidS 



Since the female color pattern is the one that prevails 

 in both sexes when there is no differentiation (e. g., Colias 

 nastes, C. hyale, etc.) I am inclined to the view that in 

 this genus of butterflies at least, as probably in birds, the 

 secondary sexual characters of the male represent a more 

 highly modified, those of the female a more primitive, 

 condition. We may recognize in this country, as in the 

 eastern continent, a natural series of species of the genus 

 Colias, at the beginning of which stands the undifferen- 

 tiated Arctic Colias nastes of Labrador, Greenland, 

 northern British America and Alaska, with the female 

 color pattern, and a dull greenish yellow ground color 

 suffused with brown, common to both sexes. This ground 

 color, as my brood of ('alias philodice, 1009, b. shows, is 

 closely related to white and probably interchangeable 

 with it. Next in the series are the subarctic ('. pclidiir 

 and C. scudderi, in the males of which the yellow color 

 and black color pattern typical of many species of Colias 

 attain their full development, while all the females are 

 clear white, with faint marginal dark bands. 



The yellow ground color and the solid black marginal 

 band probably arose by mutation in an undifferentiated 

 wastes-like or white stock, and at once became dominant 

 in the male, while the original colors and color pattern 

 remained dominant in the female. 



Southward from the range of C. pelidne, in the Cana- 

 dian faunal region, is the closely related C. interior, m 

 which yellow females (var. laurentina) occur, though 

 white females are "on the whole commoner" according 

 to Scudder, and from this region southward extends C. 

 philodice, in which the yellow females generally are far 

 more adundant than the white. Finally, the orange color 

 of C. eury theme of the central and western states, in 



