42 MAMMALS 



mother cannot do justice to a too numerous offspring, and 

 through her efforts may herself come to grief. 



Young mice are born Wind and naked, but are not long 

 before they are able to be out of the nest. They will soon 

 begin feeding, and when four or five weeks old, the young 

 bucks and does must be separated. 



The mother may now be returned to the buck, if she is 

 in good condition. 



Mice are mature when about three months old, and should 

 not be used for breeding until they have reached that age. 

 They are short-lived creatures, and when they have passed 

 two years are of little use. 



The caging of extra bucks is something of a problem. A 

 litter of youngsters reared together will generally agree, 

 although there is usually some quarreling. But adult bucks, 

 if placed together, will fight fiercely, often resulting in the 

 injury or even death of one of the combatants. The safest 

 method is to introduce several to a cage at one time, when 

 they will generally settle down, although the peace may 

 often be broken. 



Adult does may be a bit quarrelsome on first acquaintance, 

 but generally become good friends in a short time. 



Breeding mice is a diverting pursuit, and one who is in- 

 terested in heredity can gain much by this means. More 

 than thirty well-established varieties are known, and as the 

 various characters which determine them seem easily segre- 

 gated, there is no doubt that from time to time others will 

 appear. 



All of these varieties are, of course, the descendants of 

 the common house mouse (Mus musculus). This creature 

 is very subject to variation, wild mice with spots on the 

 forehead or belly being of frequent occurrence. The writer 

 well remembers several handsome wild gray agouti mice 

 caught by him when a small boy. These mice were silvery 



