﻿Manchester Memoirs, Vol. xlix. (1905), No. & 7 



you have mated it with an albino and obtained albino 

 young in the litter thus produced : until this has been 

 done there is no evidence that it is not a dominant. In 

 the case you have just shewn me you mated coloured 

 mice with dark eyes without making this test, and by 

 this neglect many dominants may have been included 

 among them, and you see that this suggestion, against 

 the truth of which you have no evidence, accounts just as 

 well as Galtonian theory for the difference in the pro- 

 portions of albinos in the three kinds of matings.' I 

 replied that the test of the true heterozygote nature of 

 the apparent hybrids should be made though I did not 

 believe the suggested Mendelian interpretation of this 

 apparently conclusive anti-Mendelian result. 



The test has been applied with the most remarkable 

 result : but before giving an account of it I propose 

 to describe my reasons for adhering to the interpretation 

 of the facts of this case which I held at first. I believed 

 that all the individuals in F 2 with pigmented coats and 

 eyes were hybrids and that when mated with albinos 

 they would all of them give some albinos ; that the 

 hybrids of F 2 differed from those of F x only in degree, 

 namely that, while it was the property of the latter when 

 mated together to produce as nearly as possible one albino 

 in every four in their litters, the former had a less albino- 

 producing capacity ; and that the hybrids of F„ would 

 each be capable of producing still fewer albinos and so 

 on with succeeding generations. My belief was that the 

 hybrids of a given generation, say F 5 , would be all the 

 same with regard to their albino-producing capacity, but 

 would differ from those of F 4 in having a smaller one. 

 Before dealing with the origin and meaning of this view 

 I will relate how, by the application of the test suggested, 

 it was shewn to be erroneous. The test of the real 



