336 THE AMERICAN NATURALIST [Vol. XL VIII 



yellow, or orange, as the case may be. Evidently, in order 

 to extract a pure white race from C. philodice or C. eury- 

 theme, it will be necessary by a mutation to obtain first a 

 homozygous white female, and then by a further mutation 

 a homozygous white male. White males are known in 

 nature as rare aberrations, but, whether they are homo- 

 zygous or heterozygous for color, it is impossible to say. 

 Among the two thousand offspring of heterozygous white 

 females of philodice and eury theme that I have bred 

 since 1908, there has been not a single white male. The 

 sons of a white female, though some are capable of trans- 

 mitting the white, are always yellow or orange. I have 

 lately, however, raised a large brood in which all the 

 females were white. This was a " back cross " between 

 a white female of the orange eurytheme and a male spe- 

 cies-hybrid (son of a white mother). Precisely similar 

 matings, however, gave both white and colored female 

 offspring in equal numbers; hence in the production of 

 this brood there was probably a mutation. From such 

 stock as this the extraction of a pure white race from 

 Colin* at some time may possibly be accomplished. 



In this connection it is interesting to note that we have 

 the testimony of a good observer, the late Mr. W. Gr. 

 Wright, 17 who made the study of Californian butterflies 

 his life work, to the effect that the white variety of Colias 

 eurytheme " is now quite common, though twenty-five 

 years ago it was a great rarity, and it was accounted a 

 feat to secure one of them, and if the present rate of in- 

 crease of the blond form shall go on, in a few hundred 

 years the normal orange-colored female will be extinct 

 and unknown." If this is a fact, and not an illusion due 

 to a general increase in the population of cunith< m> 

 owing to an increase in the cultivation of the food plant, 

 alfalfa, in that region, it may be the result of possible 

 mutations, whereby homozygous white females may have 

 been introduced into the population. It will be of inter- 



