closely spaced than the female fibers, though 

 the differences would be unimportant to a 

 furrier. The underfur fiber population of the 

 male is 11-15 percent denser than that of the 

 female. 



The effect of sex within age cannot be esti- 

 mated because the sampling program was 

 designed to provide, not seals of comparable 

 age but of comparable size. 



Effect of Location, Back or Belly 



The density of underfur fibers on the back 

 may be regarded as equal to that on the belly. 

 In the sample of 21 seals, the density on the 

 back exceeds that on the belly for 10 animals, 

 and vice versa for 11. Over all, the density on 

 the belly exceeds that on the back by 3.9 per- 

 cent. 



The underfur fibers per bundle were counted 

 in paraffin mounts representing back and belly 

 pelage of two 8-year females in nonmolting 

 condition. The counts were, respectively: back 

 44.0, belly 43.4; back 46.4, belly 38.9. 



SUMMARY 



A square of skin was taken from the back of 

 each of 321 fur seals in molt. From gross and 

 histological examination, four stages of molt 

 were identified and described. These are: 

 beginning (duration about 2 weeks), early (6 

 weeks), late (4 weeks), and ending (3 weeks); 

 total 15 weeks. Molt of the underfur precedes 

 that of the guard hair by about 1 week. Duration 

 of molt in the fur seal is similar to that in 

 Muslelavison (13 weeks) and Fu/pes /u/fa (14.5 

 weeks). 



The observed molting period was from 21 

 June to 23 January of the following year (216 

 days or 7.1 months); the probable extremes 

 are mid-June to mid-March, or 9 months. The 

 mid-date of molt is reached when growing 

 guard hair tips are nearing the outer surface of 

 the underfur layer. The mid-date is later in 

 older seals; it is slightly earlier in males than 

 in females. (Males also return to the breeding 

 islands earlier in summer than do females of 

 the same age.) The estimated mid-date of molt 



for males is 3.4 days later with each year of 

 increasing age; for females 5,5 days. The sex 

 discrepancy widens by approximately 2 days 

 with each year of age. For example, the mid- 

 dates of molt for extreme groups are: 1-year 

 males, 11 September; females, 26 September; 

 difference 16 days. Ten-year males, 12 

 October; females, 13 November; difference 32 

 days. Season of molt is dependent more upon 

 sex than upon body size. Yearlings pass through 

 molt at various times within a period of 3.5 

 months; older-than- 10-year seals within a 

 period of 5.6 months; the difference maybe(?) 

 a sampling effect. 



In the female, at least, about 25 percent of 

 the longer guard hairs are old-generation 

 fibers representing follicles which have 

 skipped a molt. 



The number of underfur follicles per bundle 

 in the first adult-type pelage is 14 to 24 

 (mean 17.9). It remains unchanged throughout 

 life. However, the number of fibers increases 

 with age, to 51 in the full-grown female and 

 68 in the full-grown male. The rise in fiber 

 count means that up to 60 percent of the fibers 

 are not shed in late molt but remain fast in the 

 bundle. The fiber count increases at the same 

 rate through age 5 in both sexes. 



The persistence of old generation (the pre- 

 ceding year's) guard hairs and underfur fibers 

 helps to maintain a heat-insulating coat on the 

 seal throughout the molting season. 



Depth of underfur is consistently near 11.5 

 to 12.5 mm., reaching a maximum of 16 mm. 

 in old males. 



Coat color of the pup changes most rapidly 

 from black to silver at about age 3 months, in 

 mid-October. 



The underfur of the adult-type pelage is 

 silvery to pale grayish brown in the yearling. 

 It is distinctly darker and browner in the 2- 

 year-old. With each increasing year of life up 

 to about 10 years, the underfur darkens almost 

 imperceptibly. In one old male the color is rich 

 cocoa brown. 



In the male, the coat becomes grizzled in 

 about the fifth year, following the eruption of 



32 



