384 THE AMERICAN NATURALIST [Vol.LYI 



garnet white. Professor Morgan writes us that he would also 

 interpret this case on the binucleated egg hypothesis. We see 

 clearly how the hypothesis may be applied and that the binu- 

 cleated eggs described by Doncaster may give indirect evidence 

 in its favor. Perhaps it is the best interpretation. "We wish 

 to point out, however, that there are other possibilities although 

 they may have no direct or indirect morphological or experi- 

 mental evidence in their favor. 



Let us assume the individual started as a normal male, the 

 single X chromosome carrying the genes for garnet and white. 

 Since the mosaic did not carry the gene for yellow, the garnet 

 white genes must have been brought together by a double cross- 

 ing over in the mother. The only assumption we need to make 

 is that during somatogenesis, the white end of one of the 

 daughter X chromosomes became in some way inactive or lost. 

 This would leave in one cell a whole X chromosome carrying 

 white and garnet; in the other an imperfect X chromosome 

 carrying garnet only. We know by test that white and garnet 

 in the same chromosome give an eye practically indistinguishable 

 from white. If one eye arose from the descendants of one of these 

 two cells and the other eye from the second cell, we could ac- 

 count for the difference in color. The only assumption we need 

 to make then is the loss or inactivation of the white gene in 

 one of the early cleavage cells. On the binucleated egg hypoth- 

 esis we must assume, first, the presence of two nuclei within 

 the egg ; secondly, that each nucleus is fertilized by a Y sperm ; 

 and thirdly, that the sex cells of the male arose from the de- 

 scendants of only one of these nuclei, as all sperm were alike, 

 carrying garnet and white. 



A second possibility is that of somatic mutation. If the white 

 gene in one of the cells should mutate to red, we would have a 

 cell whose X chromosome carried the gene for garnet. If the 

 descendants of this cell gave rise to one eye and the descendants 

 of the other cells to the second, we would have one eye garnet 

 and one garnet white, which is white. It is true that white eye 

 has never reverted to red in all the thousands which have been 

 bred. This fact renders this suggestion improbable but not im- 

 possible. 



F. Payne, 

 Martha Denny» 



