186 



THE AMERICAN NATURALIST 



[Vol. LIII 



TABLE I 



11696 Brown X 11713 Yellow 11 



11776 Brown X H'l'' Yellow 7 



11442 Yellow X Brown 6 



11562 Yellow x Brown !) 



10619 Yellow x Brown or Black 2 



The one abnormal embryo consisted of a small apparently 

 embryonic mass, with a blood clot closely jammed in between 

 two normal embryos. It will be noted that from these matings 

 97.6 per cent, of the embryos are normal and 2.4 per cent, 

 abnormal. 



When yellows are crossed inter se a very different result is 

 obtained, as may be seen from the following table, which shows 

 the result of such matings: 



TABLE II 



Yellow D X Yellow 



Yellow H X Yellow 



Yellow F X Yellow 



Yellow G X Yellow 



11867 Xll'l] 



11786 X Yellow 



Yellow E X Yellow 



11151 X 111S2 



12916 X Yellow 



Yellow J X Yellow 



11149 X Yellow 



Yellow A X Yellow 



Yellow C X Yellow 



12672 X — 99 S""ty V.'Uow 



18.7 Per cent, abnormal 

 81.3 Per cent, normal. 



From this table it will be seen that 81.3 per cent, of the em- 

 bryos produced are normal, and 18.7 per cent, are abnormal. 

 If one considers in addition the fact that Kirkham obtained 

 embryological evidence that certain embryos broke down even 

 before implantation, it seems probable that the fate of the homo- 

 zygous yellow mouse is known. 



