An Introduction to a Biology 



my reasons for adhering to the interpretation of the facts 

 of this case which I held at first. I beheved that all the 

 individuals in F,^. 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^ differed from 

 those of F-^ 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 h3"brids 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 2^5 — 

 would be all the same with regard to their albino-producing 

 capacity, but would differ from those of F ^ 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 shown to be erroneous. The test of the 

 real heterozj-^gote nature of the hybrids was made, as sug- 

 gested, by mating them with albinos. In all cases but two 

 I found, as I had expected, that albinos were produced ; 

 and I ascribed the absence of albinos from the other two 

 litters to chance, and had no doubt that I had only to mate 

 them with albinos again to obtain the required proof of 

 their hybridity. But the next litters from the two mice, 

 mated thus, contained no albinos. So that it began to look 

 very much as if these apparent hybrids really were dominants. 

 This fact in itself pointed to the truth of the suggestion that 

 mice wdth coloured coats and eyes were of two kinds — 

 hybrids and dominants ; but coupled with the result of 

 mating the gametically tested hybrids inter se it afforded 

 fairly complete confirmation of that hypothesis, for of the 

 92 young resulting from such union, 14 had a pink eye and 

 coloured coat, 58 a dark eye with coloured coat, while 20 

 were albinos. 



I wish particularly to remind the reader that I do not 

 think that these numbers are large enough to draw any 



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