CASTLE AND ALLEN. — THE HEREDITY OF ALBINISM. 613 



V. Pure and Impure Recessives. 



Although Darbishire's interpretation of his results is clearly unsound, 

 be has made an observation of great importance, both theoretical and 

 practical. In his crosses with dancing mice, he employed two different 

 stocks of white mice, and with results somewhat different in the two 

 cases. The two stocks were (1) "pure-bred" albinos purchased from 

 breeders, and presumably descended from white parents, and (2) " cross- 

 bred " albinos known to be descended from spotted [i. e. hybrid mosaic] 

 parents. The latter, when crossed (four different pairs) with the fawn- 

 white dancing mice, produced only spotted gray-white offspring, nineteen 

 in number. The former, when crossed in the same manner (five differ- 

 ent pairs), also produced gray-white mice, twelve in number, but pro- 

 duced in addition fifteen gray mice (with lighter bellies and tail) and two 



namely, albinos, dark-eyed individuals, and pink-eyed individuals, approximately 

 in the proportions, 1:2:1. 



The numbers of first- and second-generation hybrids which have been reared by 

 Darbishire are now considerable. They show conclusively that both albinism and 

 the dancing character are recessive in relation to the normal conditions. The 

 original cross between pink-eyed dancing mice and albinos has yielded 203 off- 

 spring, all dark-eyed and with bodies more or less extensively pigmented ; none 

 dance. Certain of these hybrids bred to albinos have produced 205 young, of 

 which 111 are albinos; the Mendelian expectation in this case is 102.5 albinos. 

 The remaining (pigmented) offspring of this cross are all dark-eyed like their 

 hybrid parent, and none dance ; this is precisely the Mendelian expectation. 



First-generation hybrids bred inter se have yielded both albinos and dancing 

 individuals. The Mendelian expectation is one in four of either sort. The ob- 

 served number of albinos is, as already stated, 13 in a total of 66 ; the number of 

 dancers in the entire 66 is not stated, but we are told that, in 37 mice of this gen- 

 eration, 8 were dancers ; the Mendelian expectation is 9. 



Darbishire grants that these facts are " in possible accordance with some form 

 of Mendelian hypothesis," but holds that " the behavior of eye-color is in every 

 respect discordant with Mendel's results." The latter conclusion he reaches only 

 by first assuming that " the possession of pink eyes must on Mendel's view depend 

 on a separate embryonic element from that which determines coat-color." This 

 is a wholly unnecessary assumption.^ The pigmented areas of the eye are mor- 

 phologically and (as far as heredity is concerned) also physiologically parts of the 

 general integument. A pink eye is simply an eye devoid of pigment ; it represents 

 an unpigmented area of the integument, and is no more a distinct element in hered- 

 ity than is an unpigmented (white) spot on the side or tail of the animal. In an 

 earlier paper (Castle, :03a, p. 543) one of us has likened a white animal with dark 

 eyes to a white animal with dark extremities, both are essentially mosaics of the 

 dominant and recessive,characters. On this view the observed inheritance of eye- 

 color is in every respect accordant with Mendel's results. 



