ALLEN. — THE HEREDITY OF COAT COLOR IN MICE, 109 



formed without a knowledge of these laws, which were then in process 

 of rediscovery ; but it shows clearly that a previous cross with a pig- 

 mented animal will not in any way interfere with the albino's power of 

 transmitting its albino character when paired with a second albino. 



Bateson (:03'') calls attention to the statement of Dr. C. Carter 

 Blake, printed in the fourth edition of a booklet entitled " Fancy Mice" 

 (Anonymous), to the effect that in two litters obtained from two pairs 

 of albinos, a large percentage of the young was variously pigmented. 

 This result, if true, is unique, and quite at variance with all other known 

 cases. While under certain conditions a reversal of dominance may 

 conceivably take place, it seems more than likely that either an error 

 was made in regard to the true father of the litters in question, or the 

 animals used were not true albinos. The period of gestation for house 

 mice has been shown by Sobotta ('95) to be about 21 days, and the 

 same is also true in the case of the common brown rat (Mailles, '87). If 

 proper precautions were not taken, it might well have been that in the 

 instances cited by Dr. Blake, the albino female had been covered by a 

 pigmented male just before being put with the albino male. Hence a 

 litter containing pigmented young might be born at any time within 

 three weeks after the two had been placed together, and though really 

 fathered by a colored animal, would have been attributed to the albino 

 male. Certainly such a case as Dr. Blake describes should be most 

 carefully established before receiving credence in the light of our present 

 knowledge. Another possible explanation, however, may be suggested, 

 viz., the albinos may not have been complete albinos. The occurrence 

 of mice having pigment in the eyes only has been established, and these, 

 though they might pass as albinos, are really of a very different nature. 

 This is discussed further under the head of partial albinism. 



Although pure albino mice "breed true" with respect to albinism, this 

 does not imply that all albinos have the same influence in heredity when 

 bred to pigmented animals. That this supposition is clearly erroneous 

 seems to have been first pointed out by Darbishii'e ( : 03), and Cuenot has 

 made observations leading to the same conclusion. These results are 

 more fully treated in the discussion of the behavior of colors {vide 

 infra). 



5. Summary on heredity of complete albinism. To sum up the results 

 of experiment and observation on the manner of inheritance of complete 

 albinism, it is clear that this character is recessive in the Mendel ian 

 sense to either total or partial pigmentation, so that a union of an albino 

 and a pigmented parent (the latter being understood in this case to be 



