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THE AMERICAN NATURALIST [Vol. LI 



tically at the same locus and there is consequently no 

 crossing over. 



According to the investigations of Little (1915) an en- 

 tirely similar condition obtains in regard to a dominant 

 white spotting factor {W) in mice, which, like yellow, ap- 

 pears never to occur in a homozygous condition. Whether 

 the homozygous individuals in this case also die at an 

 early stage and might be found as dead embryos has not 

 yet been determined. Little has, however, demonstrated 

 (1917) that the two factors are independent in heredity, 

 and that litters from yellows carrying W, mated inter se, 

 average only three per litter (10 litters), while similar 

 yellows mated to ww non-yellows have litters averaging 

 5 per litter (9 litters). Although the numbers are small 

 the percentage relation for the two matings, 60 per cent., 

 is quite close to the theoretical expectation, 56.3 per cent. 



LITERATURE CITED 

 Castle, W. E., and C. C. Little. 



1910. On a Modified Mendelian Ratio among Yellow Mice. Science, 

 N. S., Vol. 32, pp. 868-870. 



Cuenot, L. 



note.) Arch. Zool. Exper. et Gcner., 4* Series, Vol. 3, Notes 

 et Revue, pp. exxiii-cxxxii. 



1917. Embryology of the Yellow Mouse. Proceedings of the Amei 

 Soc. of Zoologists, Abstracts. The Anatomical Becord, Yo. 

 11, pp. 480-481. 



Little, C. C. 



1917. The Relation of Yellow Coat Color and Black-eyed White Spot- 

 ting of Mice in Inheritance Genet <t, Vol. 2, pp. 433-444. 



