20 



FANCY MICE. 



produced. One dead; six black and white young living. Here the 

 fawn-coloured element in the male has entirely disappeared, and all 

 the young partake of the characters of the female. 



" E. Fawn self -colour buck ; black and white doe. Six young were 

 produced. Three were born dead ; one is black and white, like the 

 mother, and two are fawn and white. There is no self-colour fawn 

 in the litter, yet the colours of the male and female are in some sort 

 combined. 



'•F. Albino buck ; fawn doe. Nine young produced. Two dead; 

 four albinos, like the father ; one fawn, like the mother ; one jet 

 black, and one reverted to the ' wild grey ' type. Here the black 

 element has again been produced unexpectedly, and nothing in the 

 appearance of the father or mother could have shown that they 

 might have thrown a black or a grey progeny. 



" G. Fa.wn and white buck; albino doe. Four young produced; 

 two fawn self colour, and two albinos. A theorist would, in this 

 case, have confidently speculated that the fawn self-colour would be 

 older in time than the fawn and white, but it has not been so, and 

 the progeny has reverted to a breed that no doubt existed in the 

 ancestors of the buck. 



" A consideration of these facts ought to show that the problem of 

 cross-breeding does not lie so much in a nutshell, and that it is im- 

 possible to be settled merely by offhand generalisation. 



" We have next to criticise the statement that silver-grey is obtained 

 by crossing very light black with white, or by crossing very light flesh 

 or grey with white (p. 11). Let me, therefore, repeat my corroboration 

 of the statement of Darwin (* Animals and Plants under Domestica- 

 tion,' ii., 62), that ' When grey and white mice are paired the young 

 are not piebald, nor of an intermediate tint, but are pure white, or of 

 the ordinary grey colour.' The reason for this is a philosophical 

 one, as with hybrids and mongrels it frequently or generally happens 

 that one part of the body resembles more or less closely one parent, 

 and another part the other parent ; and here again some resistance 

 to fusion, or what comes to the same thing, some mutual affinity be- 

 tween the organic atoms of the same nature, apparently comes into 

 play; for otherwise all parts of the body would be equally inter- 

 mediate in character. So, again, when the offspring of hybrids or 

 mongrels which are themselves nearly intermediate in character 

 revert either wholly or by segments to their ancestors, the principle 

 of the affinity of similar, or the repulsion of dissimilar atoms, must 

 come into action. Some experience in breeding has led me to prefer 

 the theory that silver-grey can be produced not by any intentional 

 cross whatever ; least of all by such a one as the author has sug- 

 gested, but by taking the lightest individuals and selecting from 

 them 



"Another statement is one to which I must respectfully demur. It 

 is suggested that ' one buck and six does should run together,' and, 

 again, ' any number of does up to six can run with the buck.' To 

 this I must say, that unless the does are carefully isolated, jealousy 

 in the harem is sure to supervene, and even if the adult does do noli 



