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THE AMERICAN NATURALIST [Vol. LIV 



tained as it was in Morgan's white-eyed flies and in my gray- 

 bellied agouti mice. 



Further, it would appear that another possibility, visionary 

 though it may be, exists. If factorial change within a given locus 

 is in any way influenced by other genes or combinations of genes 

 within the cell either during gametogenesis or immediately after 

 fertilization, we should expect that the w or p gene, as the case 

 might be, would be subject to different intra-cellular environ- 

 ment when its allelomorph W or P was present, from that in 

 which it would be placed in a homozygous ww or pp individual. 

 Some of the differences which are bound to exist might well make 

 for its relatively greater instability in the former as compared 

 with the latter case. 



Although such a r< lationsh i )> is highln hypothetical, it is sug- 

 gest! d that ic< should h< coutiuuuUg on the alert for evidence of 

 possible effects of'intergruic and intra-ccllular environment as 

 one of the most probable causes of genetic change. 3 



Conclusion 



It is believed that the extension of the hypothesis of partial 

 sex-linkage and of non-disjunction, the effects of which have been 

 clearly demonstrated in Drosophila should be made to .include 

 other forms only after confirmatory genetic and, wherever pos- 

 sible, cytologieal evidence have been obtained, and in the absence 

 of any other hyputhr»i s which equally t\\< experimental facts and 

 is capable of experimental proof. 



It is therefore suggested that the occurrence of occasional 

 colored females in a cross between white male and colored female 



3 It should be recognized that sex linked inheritance gives opportun: 

 the recognition of factorial changes should they occur, to a far grea 



individual, the small w might change to its epistatic allelomorph W i 

 cases without being recognized unless "each of the supposedly Ww zygotes 

 resulting from the cross were tested individually and sufficient young ob- 

 tained to determine whether they are exceptional WW individuals. This has 

 not been done on any very large scale with either birds or mammals 



If, however, the change occurred in a cross involving sex linkage, it 



