No. 612] DEATH IN UTERO OF MOUSE 743 



mating (Table IV) is somewhat higher. Theoretically, 

 if we assume that a certain proportion of embryos of 

 other gametic composition die from unknown causes in 

 mice of all colors and that all the homozygous yellows are 



TABLE III 



represented as dead embryos, then the difference between 

 the percentages of dead embryos from the yellow X yel- 

 low mating and the non-yellow X non-yellow mating 

 should be approximately 25 per cent. In our results the 

 difference is 19.2 per cent., while in Kirkham's it is 35.5 

 per cent. Neither of these is especially close to the ex- 

 pected percentage. If, however, his results and ours are 

 combined the difference is 23.0 per cent., which is close 

 to expectation. 



If instead of comparing yellow X yellow with non-yel- 

 low X non-yellow only, all matings other than yellow 



