316 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



it is usual to see individuals in perfect summer garb as to the anterior 

 half of their bodies, though without a particle of overhair on the pos- 

 terior half, excepting the tail, which retains the winter coating until 

 this time, new hair beginning to appear just as the summer coat has pro- 

 ceeded backward from the nose to a point behind the shoulders. Twent}" 

 adults, taken from September 3 to December 21, fail to show clearly 

 the progress of the change from summer to winter coat, though a con- 

 siderable change does take place, as is instantl}^ appreciated when speci- 

 mens in fresh summer coat are compared with those taken in December, 

 when the winter coat is prime. In the summer pelage underf ur is absent 

 on the l)ell3% the skin appears between the sparse overhair, and the hair 

 is short throughout. In winter the bell}' is well covered with underfur, 

 and the entire coating longer. There are no positive color differences. 

 In July and August the posterior half of the l)ody usually becomes sun- 

 burnt, and changes to a dull, ])rownish color. When the overhair falls 

 out in masses the plumbeous underfur soon changes to the same brown 

 color until replaced by the incoming sunmuM* pelage. Lactation seems 

 to exert but little influence upon the season of molting. Males ac(juire 

 the summer coat, as a rule, no earlier than females. Quite A'oung speci- 

 mens were collected from July to November, showing that the season of 

 reproduction is quite irregular or that more than one litter of young is 

 raised in a season. The young are similar to their parents, but with 

 the colors brighter and often more strongly washed witii Itrownish 

 posteriorly. 



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Arizona. 



a American Museum of Natural History. 



