96 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ill conjunction with Dr. S. M. Copeman. In Table K are summarized the 

 cases in which both parents were heterozygotes and produced both pig- 

 mented and albino young. 



These results are quite similar to those previously reviewed. In a 

 total of 63 mice, the albinos appear in practically their calculated propor- 

 tion, being 14 in number instead of 15.75, which is as close an agreement 

 as might reasonably be demanded. In six of the ten litters, the albinos 

 are in excess, the total excess being 4.25 individuals, yet this is more 

 than offset by the shortage in the four remaining litters, amounting to 6 

 individuals. In one case, no albinos occurred in a litter of 8, and again 

 none in a lot of 7 young. In other cases the two classes, pigmented and 

 albino, occurred in equal numbers in separate litters, though in none did 

 the albinos outnumber the pigmented mice. In 21 cases, albino mice 

 were bred to heterozygous individuals, so that 50 per cent of the 

 offspring are expected to be albinos. The following table (L) shows 

 the results of these niatings. 



As pointed out by Bateson, the expected equality of the pigmented and 

 the albino classes is here realized. One black-white male bred to several 

 albino females produced in all 27 pigmented to 31 albino young; and a 

 brown-white male under similar circumstances produced 11 pigmented to 

 19 albino mice. In these two cases the 1 : 1 ratio is rather closely 

 approximated. On the other hand, four heterozygous females, bred to 

 albino males, give IG })igineuted and 7 albino young, which Bateson 

 believes can hardly be a fortuitous departure from the expected equality. 

 Yet the departure is actually but 4 or 5 individuals, and may be entirely 

 a matter of chance. For even the black- white male, previously men- 

 tioned as producing a very nearly equal number of the two sorts of 

 gametes, at one time fathered a litter consisting of 5 albinos by an albino 

 female. Indeed, the record of this male shows that although in the long 

 run the two sorts of gametes are produced in relatively equal numbers, 

 yet, as pointed out in other cases, separate litters show that there is con- 

 siderable variation in the proportions of the two sorts of gametes which 

 are fertilized at each mating. 



To sum up, it would seem to be conclusively proved that among house 

 mice, fancy mice, and rats, complete albinism is inherited strictly in ac- 

 cordance with the Mendelian principles. Investigations have up to this 

 time shown no clear cases of deviation from the common 3 : 1 and 1 : 1 

 ratios of pigmented to albino individuals when any considerable number 

 of offspring is taken into consideration. 



(3) Complete albinism and two other coat characters. In the cases 



