long, colorless guard hairs which may compose 

 up to one-third of the longer hairs on the back. 



Mean slant depth (or depth in the plane of 

 the hair roots) of the dried dermis is 3.8 to 

 4.0 mm. in silver pups. In the male it in- 

 creases with age to 8.9 mm., in the female 

 to 5.8 mm. The thickness increases signifi- 

 cantly with age and with molt. 



The sweat gland does not reach full size until 

 the seal has entered its second year. From 

 morphological evidence, the gland is probably 

 functional by the time the seal, as an autumn 

 yearling, returns to land. Fat cells clustered 

 around the base of the gland follow a similar 

 schedule to maturation. They descend, with in- 

 creasing age of the seal, from a slant depth of 

 2 mm. to a depth of 5 mm. Old females, at 

 least, have an oilier skin than young females. 



Sebaceous glands are functional at birth. 

 They may (?) increase in size with age and 

 with molt, though the sample is too small to 

 prove or disprove it. 



In a selected sample of old females, body 

 weight increases during spring, when the seals 

 are feeding at sea. From June to November it 

 drops slightly and, though data are lacking, it 

 evidently drops sharply in December. The de- 

 cline coincides with the mid-date of molt in 

 old females. 



The fiber-bundle count per cm. 2 decreases 

 with age of seal (and increased area of body 

 surface). The count for a 3-year male is 1,296 

 bundles per cm. 2; for a 15-year female, 790. 

 In seals of similar size, subadult males and 

 adult females, the fiber-bundle count is similar 

 for both sexes and for back as compared with 

 belly. In the back pelage of the 12-year female 

 there are estimated to be 929 guard hairs and 

 41,805 fur fibers per cm. 2, or 275,634 total 

 fibers per inch. 2 



ACKNOWLEDGMENTS 



Fisheries Research Boardof Canada, collected 

 some of the study samples. Douglas G. Chap- 

 man, of the University of Washington, advised 

 on statistical methods. 



LITERATURE CITED 



BASSETT, CHARLES F 



and LEONARD M. 

 LLEWELLYN. 

 1948. The molting and fur growth pattern in 

 the adult silver fox. American Midland 

 Naturalist, vol. 39, no. 3, p. 597-601 



BARTHOLOMEW, GEORGE A., JR., and PAUL 

 G. HOEL. 



1953. Reproductive behavior of the Alaska 

 fur seal, Cailorhinus ursinus. Journal of 

 Mammalogy, vol. 34, no. 4, p. 417-436. 



BISSONNETTE, THOMAS HUME. 



1935. Relations in hair cycles in ferrets to 

 changes in the anterior hypophysis and to 

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CARTER, H. B., and W. H. CLARKE. 



1957. The hair follicle group and skin 

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DANFORTH, C. H. 



1939. Physiology of human hair. Physio- 

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DOLNICK, ETHEL HELEN. 



1959. Histogenesis of hair in the mink and 

 its relationship to dermal fetal fat cells. 

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MARGOLENA, LUBOW A. 



1954. Sequence and growth of primary and 

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The senior author is responsible for histo- 

 logical observations; the junior author for 

 statistical treatment of the findings. Ian B. 

 McAskie and Gordon C. Pike, both of the 



MUNSELL COLOR COMPANY. 



1954. Munsell soil color charts. Pub. by the 

 Company, Baltimore, 6 p. and 9 color 

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33 



