1903.] IN FANCY MICE AND RATS. 85 



the blw. c? a the albino gametes equalled the browns and the 

 blacks collectively, for with various albinos he gave 27 coloured 

 {q-v.), 31 albinos, a near approach to equality. As regards the 

 brw. c? 7, the evidence is that with 3 albinos he gave 1 1 coloured, 

 19 albinos. On the other hand, 4 heterozygous coloured females 

 xw. c^e gave 16 coloured, 7 albinos. As the result of the 

 reciprocity of these numbers, the total (adding expt. 23) of 

 coloui-ed to albinos, produced by all matings in the form DE, x R, 

 is exactly 59 to 59. It is, however, difficu.lt to believe that the 

 departure from equality just named is simply fortuitous, for it is 

 in each case steadily maintained through a series of families. If 

 the figures are grouped according to mothers (instead of fathers, 

 as here) these peculiarities are partly lost, but further experiment 

 may possibly indicate that different kinds of heterozygotes are 

 here to be distinguished. 



Of matings in the form DR X DR there are ten cases, expts. 

 26-7, 32-4, 37-8, 42-4 giving a total of 49 coloured, 14 albinos, 

 the simple Mendelian expectation being 47 "25 to 15 "75. 



In these experiments there is also good evidence of the appear- 

 ance of dominants containing no albino, for example brw. cS 

 (0'^"'), and probably blw.C\ 



Information given me by Mr. J. Wilson Steer and Mr. Atlee, 

 and the experiments lately begun by Miss Durham and Mr. Staples 

 Browne, enable me to add a few indications as to the probable 

 specific behaviour of some of the colour-types in crossing, though 

 these have at present only the value of hints for furthei- 

 experiment. 



The agouti {Mus muscidus colour) is of course dominant to 

 albino, but so far has not been resolved in F,, having apparently 

 the same behaviour as the wild colour in Cuenot's experiments, 

 but sometimes piebalds of agouti and white appear. 



Yellow and black crossed have given sables or " dingy fawns." * 



Chocolate x albino may give, according to Mr. Steei", the wild 

 musGuhhs colour, doubtless by reappearance of the black pigment 

 in association with brown of the chocolates. Probably the strains 

 used had other differences also {cf. p. 97). Miss Durham has found 

 chocolate a simple dominant over albino. 



Sable X black-and-white, according to the same authority, has 

 given sables, though in this case the result will probably be found 

 to differ according as the black-and-white is homo- or heterozygous. 



Sables bi-ed together have given sable, black, and dingy fawn in 

 the same litter. 



Blue X albino has given a full black, sometimes with white 

 patches on tail. 



Two yellows (from an inl^red strain 4 years old) gave 1 yellow 

 and 2 chocolates {Steer). This last occurrence is unexpected and 

 needs careful ^•erification. 



* More recently Miss Durham has thus bred some full blacks. Eeliable and 

 extensive information as to the result of mating j'ellows with blacks is greatly needed. 



