Interpretation of the Evidence 



The presence of old-generation guard hairs 

 in the fresh, resting pelage might be inter- 

 preted in two ways. Either (a) each old hair is 

 an unshed "holdover" twinned with and emerg- 

 ing from the same pore as a younger com- 

 panion, or (b) each old hair is standing alone 

 in a follicle which was inactive in the last 

 molt. Since in subsurface sections of resting 

 skin twin hair stumps are not present, each 

 old hair must in fact represent an inactive 

 follicle. 



The percentage of old hair shafts is roughly 

 25, and the maximum percentage of twin hair 

 stumps, each of which represents the renewal of 

 a hair, is 73. If a maximum of about 75 per- 

 cent twin hair stumps is attained in an individual 

 when, temporarily, all of the old hairs are 

 present with all of the new ones, then, for 

 mature seals at least, about 75 percent of the 

 resting guard hairs would be new generation 

 and 25 percent would be old. 



Is the ratio of new to old hairs, or annual 

 rate of replacement, similar for seals of all 

 ages? Twin hair stumps are less abundant 

 in seals of ages 1, 2, and 3 than in older seals. 

 The increase with age could mean that shedding 

 is more prolonged in old seals and prompter 

 in young ones, or it could mean that the annual 

 replacement of hairs in old seals is more 

 complete--more extensive. The evidence 

 available does not answer this question. 



Incomplete molt of the guard hair was 

 demonstrated in the course of marking ex- 

 periments carried on by R. S. Peterson in 

 the summer of 1961, He marked a number of 

 bulls by clipping (shearing) or by chemically 

 bleaching patches of hair. In letter of 3 June 

 1962 he wrote that "the clipped areas have 

 grown out but the new guard hairs are a . . . 

 lighter shade than the old; while the bleached 

 hairs are still retained, though less prominent 

 than before." His observations may be in- 

 terpreted as follows: On clipped areas all of 

 the hairs seen in 1962 were new ones with 

 unbroken white tips, and they were only three- 

 fourths as abundant as hairs in the surround- 

 ing unmarked pelage. On bleached areas, 

 three-fourths of the hairs seen in 1962 were 



presumably new, undamaged ones, and one- 

 fourth were unshed bleached hairs of the old 

 generation. 



Danforth (1939, p. 109) found that human 

 hairs "show a remarkable degree of autonomy, 

 which is maintained over long periods and is 

 not readily disturbed by external factors. Each 

 follicle has its own individual rhythm . . . ." 



PERSISTENCE OF OLD-GENERATION 

 UNDERFUR FIBERS AFTER THE MOLT 



Whereas old guard hairs are distinguishable 

 from new by the amount of fading and wear of 

 the shaft, the same test cannot be applied to 

 underfur fibers . These are buried in the pelage 

 and do not become faded or worn. Underfur 

 roots provide the only evidence. 



The Number of Underfur Fibers per Bundle 



The number of underfur fibers per bundle 

 was counted in 20 bundles for each of 120 

 seals. The results are given in table 10; 

 selected data are given below: 



Minimum count for any bundle (a 

 1-year female in January and a 1- 

 year male in February) 9 



Minimum mean count for any seal 

 (a 1-year male in February) 14.0 



Maximum count for any bundle (an 

 old male in September in early 

 molt) 89 



Maximum mean count for any male... 67.7 



Maximum mean count for any female 50.8 



Mean count for all seals 39.2 



Variation in Number of Fur Fibers with Age 

 and Sex 



In both sexes, in the first adult-type pelage, 

 the underfur fiber count per bundle is 14 to 

 24 (mean 17.9). These figures are based on 15 

 of the 21 silver pups and yearlings represented 

 in table 10, to the exclusion of 6 yearlings 

 which are in, or have passed through their 



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