32 



NORTH AMERICAN FAUNA 68 



Figure 14. — Hair from the midback of adult male sea otter D22-57. The outer 

 surface of the underfur layer is not distinct; the soft, wavy tips of the 

 fur hairs blend with the tips of the smaller guard hairs. (VBS 5710) 



two overlapping groups which I call "larger" and "smaller," with few inter- 

 mediates. For example, here are the diameters of 10 roots in one field of view 

 under the microscope: 14, 15, 16, 18, 20, 25, 26, 33, 38, and 64 microns (cf. 

 fig. 16). Cross sections of the guard hair roots are oval to nearly round in 

 outline; they vary in diameter from 13 to 64 microns (average 25). 



In five bundles I count 60 to 80 (average 71) underfur roots per bundle. 

 The counts in two other specimens are: (KWK 59-13, old female, 9 February 

 1959) 79-110 (average 91); (KWK 59-51, young male, 7 March 1959) 

 40-45 (average 43). Comprehensive studies of pelage samples from different 

 seasons and different age groups of otters will be necessary before the ex- 

 tent of holdover of pelage hairs can be evaluated. Cross sections of the under- 

 fur roots are roundish ova], smooth, fairly uniform, and 6.3 to 8.5 microns 

 (average 7.2) in diameter (fig. 16.) 



A disc of skin-with-pelage cut by trephine from the formalin-preserved, 

 mid-back specimen measured 0.4 cm^. It contained 520 bundles or 1,400 per 

 cm^ (fig, 17). [That there is considerable variability is demonstrated by the 

 finding by J. K. Ling (MS) of 2,176 follicle bundles per cm^ on a sample of 

 facial skin.] On the basis of 71 underfur hairs and 1 guard hair per bundle, 

 (hairs per cm-' = 72 x 1400 = 100,800 or 650,160 per in.^) and an estimated 

 area of 8,000 cm^ for the total hair-covered surface of the body, the pelage of 

 an adult male sea otter would contain about 800 million hairs. 



Above the surface of the skin, the shaft of each larger guard hair is a 

 typical awn or shield hair, flattened into a blade near the tip. At a level 10 



