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THE AMERICAN NATURALIST [Vol. XLIX 



be a bar (heterozygous) eyed, long- winged female, since 

 these are the dominants. If, then, after fertilization, dis- 

 location of the X chromosomes occurred at some early 

 division, so that while the X carrying the factor for 

 bar and long divided normally (each daughter nucleus 

 getting its proper half), the other X chromosome carry- 

 ing the factors for round eye and long wings failing to 

 divide (or else one half failed to go to one daughter 

 nucleus) the characteristics of the mosaic can be ac- 

 counted for. On the male side, the left, there would be one 

 X chromosome in each cell, that carries the factors for 

 bar eye and long wings. The size of the wing and of the 

 spines, and the presence of the sex comb are a consequence 

 of the "maleness," resulting from the presence of only 

 one X. On the female side, the right, there would.be two 

 X chromosomes in all of the cells, hence the heterozygous 

 nature of the bar eye. The length of the wing (the female 

 being larger than the male) and the absence of the sex 

 comb are a consequence of the " fenialeness, " due to the 

 two X combination. The fact that the posterior end of 

 the abdomen is purely male is owing to this region coming 

 from the male contingent of nuclei, that must have over- 

 lapped to the right side in this region. 



The other explanation of the mosaic is that two female 

 producing nuclei entered, one alone giving rise to the 

 male side, the other one uniting with the egg nucleus giving 

 rise to the female side. Boveri's explanation of gynan- 

 dromorphs will not apply to this case. There is no way 

 to decide between the first two hypotheses, but, as I 

 have shown elsewhere, 2 the hypothesis of chromosomal 

 dislocation will cover all eases of gynandromorphs in 

 Drosophila, while that of double fertilization will not ap- 

 ply to one case that gives, for itself at least, a crucial test 

 of the alternative hypotheses. The hypothesis of chro- 

 mosomal dislocation is, therefore, to be generally pre- 

 ferred, unless in some special case it can be shown that 



2 "Mosaics and Qynaitdromorphi in VroaophO*/' Proc. Soc. Exp. Biol, 

 and Med., XI, 1914. 



