DOMESTIC RATS AND MICE 47 



obscurity. The balancing apparatus of the inner ear of this 

 mouse is imperfect, causing the animal to turn constantly 

 in short circles. This defect is strongly fixed, and trans- 

 mitted with regularity to the young. 



Waltzing mice generally are white with black spots, but 

 chocolate- and red-spotted ones are occasionally seen. There 

 is no doubt that other colors could be bred with little diffi- 

 culty. The writer has seen second generation young bred 

 from a cross with white mice that possessed the turning 

 character.very strongly. 



Waltzing mice, perhaps from long and indiscriminate 

 inbreeding, generally are weak and lacking in stamina. 

 They are not so easily bred as other varieties, but their care 

 in general is essentially the same. 



Fancy Rats 



For some obscure reason, domesticated rats appear to 

 be more widelydistributed, as pets, than mice. During the 

 writer's boyhood, white rats were common enough, but 

 white mice were unheard of.' Although bred in great num- 

 bers, for experimental and other purposes, there is little 

 variety of color among rats. Until very recently, white, 

 black and gray were the only ones known. But within 

 the last two or three- years two very attractive colors — 

 yellow or orange, and cream — ^have been perfected. The 

 origin of these colors is of great interest, and will be con- 

 sidered later on. 



The domestic varieties of rats are descendants of the 

 common brown or Norway rat (Mus norvegus). 



No doubt the older colors developed in the same manner 

 as in mice, albinism being the first variation. 



Rats do not have the strong odor of mice, and for this 

 reason, at least, are less objectionable. Also, they are less 



