CASTLE AND ALLEN. — THE HEREDITY OF ALBINISM. 605 



The precise numbers recorded are 162 grays : 57 albinos, or 26 per cent 

 albinos. 



Ciieuot's observations are fully substantiated by experiments performed 

 by the junior author of this i^aper, a full account of which will be pub- 

 lished elsewhere. Wild gray mice were crossed with albino mice, and 

 the offspring, sixty-four in number, were all gray like the wild parent, 

 though a single litter of three youug, which died without attaining their 

 full growth, were of a somewhat lighter gray than the wild parent. 

 Certain of the cross-breds were paired together, and produced 66 off- 

 spring, 42 of which were gray, 24 white. This is a considerable devia- 

 tion from the expected ratio, 3:1, but it should be remembered that 

 the total number is relatively small. The result is of the nature ej^pected, 

 in that both gray and albino offspring are produced, and of the former a 

 larger number than of the latter. 



To determine whether the grays are, as expected, of two sorts, one 

 hybrid, the other pure, six pigmented individuals have been crossed with 

 the parental white stock. Three of the six have thus far produced only 

 pigmented offspring, indicating that they are pure ; the other three have 

 produced both gray offspring and white offspring, showing that they are 

 hybrids. The two sorts of offs[)ring produced in the case last mentioned 

 should, according to Mendelian expectation, be equally numerous. 



The numbers thus far recorded are 35 pigmented individuals: 23 

 albinos, a result agreeing with expectation in that both gray and white 

 offspring are produced, though these are not in the exact proportions 

 demanded by Mendel's laws. 



If we combine the results of this cross with those obtained by inter- 

 breeding hybrids of the first filial generation, we get for the whole a 

 close agreement between expectation and observation. The expectation 

 is 78.5 gray : 45.5 white; the observed result is 77 gray : 47 white. 



White mice obtained by one or the other of these crosses have repeatedly 

 been bred together, but without the occurrence of a single exception to 

 the expected Mendelian result, the offspring being invariably albinos. 



A further test of the Mendelian hypothesis as applied to albinism in 

 mice was made by Cuunot. V>y back-crossing hybrid grays with the an- 

 cestral white stock he obtained gray as well as white individuals, which 

 in the phraseology of breeders should be i, 2, |. etc., white "blood," yet 

 all the grays, irrespective of ancestry, gave precisely similar results in 

 crosses with whites, viz. equal numbers of gray and white offspring. 



It is evident, then, that when a pure gray race of mice is crossed with 

 a pure white race, the gray character invariably dominates in the off- 



