THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 37 



the exterior ends of the cutaneous gland ducts. There are no glands opening 

 into the underfur follicles (fig. 19). 



Adaptations of the sea otter integument to an aquatic habit include (1) 

 only periodic occurrence of the granular layer which may confer upon the 

 horny layer different properties from those arising from the continuous 

 presence of granules, thereby contributing to its water-resisting function; (2) 

 the flattened guard hairs; and (3) the absence of arrector pili muscles 

 enabling the hairs to lie close to the skin surface when the animal enters the 

 water. These features are exemplified by the fur seals and they may be 

 common to all semi-aquatic mammals. In common with other densely furred 

 species the sea otter has large functioning apocrine sweat glands associated 

 with each guard hair follicle. 



Sensory vibrissae 



Sensory vibrissae are in three locations : mystacial, superciliary, 

 and nasal. The numbers of vibrissae are for the left side only 

 of an adult male. There were 8 rows including 62 mystacial vib- 

 rissae (i.e., total both sides 124 mystacial vibrissae). The largest 

 was 53 mm. long and the shortest 2 mm. There were four super- 

 ciliary vibrissae, the largest (dorsal) was 33 mm. and the three 

 others were about 12 mm. long. There were three nasal vibrissae 

 (along the dorsal anterior nasal area), each about 14 mm. long. 



The mystacial vibrissae are the most important as sensory 

 organs. They are voluntarily controlled and are frequently ex- 

 tended forward. In this position they are used as sensory aids 

 when walking among rocks or when examining a strange object. 

 Presumably they are used when exploring the bottom of the sea 

 for food. In the wild they are often worn off short but in captivity, 

 where a search for food is not necessary, they may reach a length 

 of 100 to 120 mm. 



MOLT 



Maynard (1898) wrote that **Their fur is considered equally 

 good at all seasons ; hence they are hunted throughout the entire 

 year." Similar statements were made by many other authors. 



The lack of an observable molting season may perhaps be ex- 

 plained by analogy with molt in the fur seal. Scheffer and Johnson 

 (1963, p. 32) found that "The number of underfur follicles per 

 bundle in the first adult-type pelage . . . remains unchanged 

 throughout life" but that the number of fibers in each bundle 

 increases with age. "The rise in the fiber count means that up to 

 60 percent of the fibers are not shed in late molt but remain fast 

 in the bundle." 



Scheffer demonstrated earlier in the present report that a young 



