Figure 8. --Number of underfiir fibers per bundle, by 

 age and sex: quadratic curves fined to the data of 

 table 11. (Male, (Y = 14.76 + 5.99 X - 0.236 x2; 

 female, Y = 14.89 + 5.90 X - 0.290 X^ ). 



many age classes. To look for fiber count 

 changes correlated with season, it is necessary 

 to follow the trend of one age class, or a few 

 similar age classes. Where the sampling was 

 good, for example, of 2- and 3-year males, and 

 3-, 4-, 5-, and> 5-year females, the data by age 

 indicate that the fiber count remains unchanged 

 during winter, spring, and summer when the 

 pelage is resting. The fibers are held fast in the 

 bundle. As might be expected, the count rises 

 during molt in autumn, when new hairs are 

 erupting faster than old ones are belngshed.lt 

 subsequently declines to the resting level. 



The Number of Active Underfur Roots per 

 Bundle 



The counts of underfur fibers were taken near 

 the surface of the skin. Deeper in the skin of an 

 actively molting seal, however, the fiber count 

 is lower. For example, in an 11-year male in 

 early molt, the mean surface count is 56,0 (47 to 

 61), while the count just below the level of the 

 sweat glands is only 19.8 (15 to 27), Further- 

 more, at deeper levels there are only well- 

 formed follicular bulbs, while at shallower 

 levels there are shafts of these bulbs and also 

 shafts without bulbs. 



Interpretation of the Evidence 



It has been shown (a) that the underfur fiber 

 population per bundle rises, with increasing age 

 of the seal, from about 18 to about 51 in the 

 female and 68 In the male and (b) that during 

 active molt thepopulationof follicles with bulbs 



in the deeper dermis is about the same, regard- 

 less of age of seal, as it was in the original 

 pelage. 



The deduction is made that the seal has, at a 

 time no later than its first autumn, and more 

 likely in utero, all of the underfur germs it is 

 ever to have. As the surface area of the skin in- 

 creases, the fur bundles become less crowded, 

 and increasing numbers of fibers remain in 

 place, unshed, after each new crop has erupted. 

 When growth of the surface area ceases, the 

 fur fiber count levels off. 



The phenomenon of fiber retention beyond the 

 molt may be summarized as follows: In the 

 guard hair layer, fibers more than a year old 

 represent individual follicles which skipped the 

 last molt. In the underfur layer, fibers more 

 than a year old represent follicles which were 

 pushed aside by the last erupting crop and 

 which have not yet shed their fibers. Here the 

 fur bundle holds all of the fibers, new and old, 

 that it can. In the mature seal in resting stage, 

 the percentages of new and old fur fibers are 

 about 25:75 for the male and 33:67 for the 

 female, (These percentages are calculated from 

 counts, table 10, The percentages calculated 

 from smoothed counts, table 11, wouldbe 28:72 

 and 33:67, respectively,) 



It is reasonable to suppose that "reluctant 

 shedding," or the persistence of old-generation 

 guard hairs and underfur fibers, has survival 

 value to the seal. It helps to maintain a heat-in- 

 sulating coat throughout the molting season. 



This interpretation agrees with the findings of 

 Margolena (1954, p. 765). She started with the 

 premise that "once a tissue is differentiated it is 

 usually incapable of producing new organs" and 

 found that, in Karakul sheep, all follicles are 

 established in fetal life and their population 

 remains constant. 



It has not been determined what fraction, if 

 any, of the underfur follicle population remains 

 inactive during molt. Nor has it been deter- 

 mined what fraction, if any, of the fiber popu- 

 lation remains in place for longer than 2 years. 



CHANGES IN DEPTH OF THE PELAGE 



Measurements of the depth of the guard hair 

 and underfur layers on tanned sealskins were 

 reported by Scheffer (1962, p. 72). 



22 



