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NORTH AMERICAN FAUNA 74 



in the temperate zone evidently begins and ends much earlier than that of any 

 of their free-living counterparts. More information is needed to clarify these 

 points, but their implication is that the annual molt is triggered as much by 

 thermal as by photoperiodic stimuli. 



The possibility that heating and suffusion of the skin with blood were of major 

 importance in accelerating the molt of pinnipeds first occurred to me at Round 

 Island in June 1958, when I observed that the walruses having most of their 

 pelage intact showed complete depilation about their partly healed superficial 

 wounds. At the same time, the animals which already had shed most of their hair 

 showed fully developed new pelage hairs about their healing wounds. Because, 

 in my experience, wound-healing is associated with both congestion and heating 

 by blood, I suspected that the more rapid molt about the walruses' wounds was 

 facilitated by those two factors, which are closely linked in these mammals (Fay 

 and Ray 1968; Ray and Fay 1968). 



That the growth of hair and other epidermal appendages of mammals is 

 accelerated by warming and hyperemia and is depressed by cold and ischemia 

 has been reported in many other contexts (e.g., Haddow et al. 1945; Hale 1945; 

 Storey and Leblond 1951; Montagna 1956; Heroux 1960; Sapin-Jaloustre and 

 Sapin-Jaloustre 1956 in Heroux 1960). Although one might expect the epidermis 

 of walruses to be enzymatically adapted for metabolism and growth at low tem- 

 peratures, my observations of hair growth about healing wounds and more rapid 

 and complete molts at Round Island than farther north, were contraindicative of 

 such adaptation. When the walrus is immersed in the cold water of the Bering 

 and Chukchi seas at about -2 to -i- 10°C, its skin is about as cold as the 

 surrounding medium and is generally deprived of blood (Fay and Ray 1968). At 

 those temperatures, the cutaneous cells of walruses and other pinnipeds seem to 

 be incapable of proliferation (Feltz and Fay 1966). When the animal emerges 

 from the water and is warmed by the ambient air and solar radiation, the skin is 

 suffused with blood. The provision of both heat and nutrients apparently allows 

 the epidermal cells to proliferate. The greater the heat and suffusion, as with 

 decreasing latitude or increasing amount of time spent on the haulout, the more 

 rapidly the molt seems to be completed. 



Facial Vibrissa e 



The pinnipeds possess three kinds of facial vibrissae: rhinal, superciliary, and 

 mystacial. Rhinal vibrissae occur only in certain phocids (Ling 1966, 1977); the 

 superciliaries are prominent in phocids but weakly developed in otariids (Schef- 

 fer 1962); the mystacial vibrissae are highly developed in all pinnipeds. None of 

 the walruses that I examined possessed any rhinal vibrissae or vestiges thereof, 

 but I found superciliary vibrissae often in fetuses and newborn calves. These 

 usually numbered one or two (rarely three) above each eye, and sometimes 

 attained a length of 1 cm. They rarely were noticeable in animals more than a 

 few weeks old, but I did not determine whether their apparent absence was due 

 to their having been shed or merely abraded or broken off. The mystacial 

 vibrissae, however, were well developed in all of the specimens that I examined, 

 and I saw no evidence of their ever being shed or replaced. Mohr (1950) and 

 Yablokov and Klevezal' (1964) reported that they range in number from about 



