Age Classes and Patterns of Primeness in a Fall Collection of Muskrat Pelts

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Abstract
Between Oct. 13 and Dec. 9, 1946, 64 muskrats (Ondatra zibdhica) were trapped and pelted. 61 of these were taken from the Huron River drainage, Washtenaw Co., Michigan. All pelts were photographed for permanent record. Some difficulty in portraying all details of primeness were encountered in the photographing due to the unevenness, red color, and oily nature of the pelts. Excellent pictures were obtained by employing a low-angle for subject illumination and panchromatic film. Kodabromide F-4 and F-5 projection paper yielded pictures of high contrast from low contrast negatives. Prior to pelting, the specimens were separated into subadults and adults by the condition and/or development of the external genitalia. The subadults were further divided into 2 classes according to certain characteristics of prime and unprime pelt patterns. When 60 pelts were accumulated, the specimens were sorted into 3 age classes: (1) small subadults; (2) large subadults; and (3) adults, on the basis of patterns of primeness alone. The validity of this method was tested by comparing the individuals of each age class with its age class as previously detd. by the external genitalia. 58 of 60 specimens had been correctly aged. In the 13 adult muskrats the characteristic pattern of priming is erratically located areas of prime and unprimepelt. 38 large subadults were characterized bya"lyre-shaped," dorsally located, band of creamy-white prime area changing into a solid area of prime pelt bounded by an encompassing band of blue-black unprime pelt. The 7 small subadults differed from the large subadults by a sharper differentiation between prime and unprime areas.

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