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THE AMERICAN NATURALIST [Vol. LIV 



This would account for the exceptional colored females, re- 

 ported from this cross by Staples-Browne and by Strong. It also 

 expects an additional exceptional class— namely white males, and 

 these, though they should occur as frequently as do the colored 

 females, are conspicuous by their absence. 



Further than this the hypothesis as just outlined supposes 

 that "crossing over" occurs in the heterozygous sex, between 

 chromosomes which correspond to the X and Y chromosomes of 

 Drosopfoila. This condition has not been observed in Drosophila 

 or in forms where a similar opportunity exists and it must there- 

 fore, be considered as entirely hypothetical and contrary to such 

 evidence as the most extensively investigated forms have given. 1 



2. Canaries. — In this form, the sex-linked inheritance of the 

 factor for dark-eyed color (P) having as an allelomorph pink 

 eye color (p) has been demonstrated by Durham and Marryatt 

 (1908) and reviewed by Sturtevant (1912). Here, however, as 

 in doves there is an unexpected color class which makes its ap- 

 pearance. The exceptional individuals are dark-eyed females 

 which occur in a cross between pink-eyed males and dark-eyed 

 females where only dark-eyed males and pink-eyed females are 



Sturtevant. in reviewing the case and in attempting to explain 

 it as the result of partial sex linkage says (p. 570) : 



This hypothesis could be easily tested. If it is correct, then 

 , the cross just discussed should, if large enough numbers be 

 reared, produce as many pink-eyed males as black females." The 

 occurrence of such pink-eyed males has not been reported al- 



would have been observed and mentioned by breeders did they 

 occur even very rarely. 



We may, therefore, say that should the missing color classes 

 appear in the dovi and canary matings as predicted by the 

 hypothesis of partial sex linkage, that hypothesis would have a 



but not in the female. This result serimMv invalidates partial sex-linkage 

 as a possible explanation for the exceptionally colored females in doves or 



