44 



NORTH AMERICAN FAUNA 74 



My material was obtained from subadult and adult walruses taken in the 

 Bering Sea in January to June, August and December, and from calves taken in 

 April to July. Material from fetuses was obtained from August to January and 

 March to May. 



The hair and surface of the skin were inspected in place on the carcasses, and 

 total thickness of the skin (epidermis and dermis) was measured with a metric 

 ruler in incisions at selected locations, taking precautions to avoid distortion of 

 the tissue. Samples for histological study usually were taken several hours after 

 the death of the animal and, in a few instances, after portions of the carcass had 

 been in frozen storage (-10 to -40°C) for several months. Strips of skin, 1 to 3 cm 

 wide and 5 to 10 cm long, were fixed usually in 10% formalin; a few were fixed 

 in acetic-formalin-alcohol (AFA) or in Bouin's fluid. Microsections were pre- 

 pared from small blocks, mostly about 0.5 cm^ in volume, cut from the outer 

 surface of the strips. These were dehydrated in ethanol, embedded in paraffin or 

 celloidin, sectioned on a rotary microtome at 7 to 25 /xm, and routinely stained 

 with haematoxylin-eosin dye. 



General Appearance and Thickness of Skin 



The skin of the calf at birth is uniformly leaden gray to gray-brown, and has a 

 thin coat of fine hair, about 5 mm long, of similar color. In the succeeding 

 weeks, the pigmentation of the skin becomes more intense, and the lengthening 

 hair becomes characteristically light brown. By the second week after birth, the 

 hairless flippers are charcoal gray, and the pelage is light reddish-brown; by the 

 end of the third week, the flippers are nearly black and the pelage, now about 7 

 to 10 mm long, is rusty brown to tawny, as though bleached somewhat by the 

 sun. I noted these changes in calves held in captivity at Gambell during May 

 1958, 1959, and 1961. Comparable stages were recognized in the calves har- 

 vested by Eskimos during the same periods. The contrasting pigmentation of two 

 of those calves, the first about 1 h old and the second perhaps 3 to 4 weeks old, is 

 illustrated in Fig. 29. 



The skin probably is more intensely pigmented in these 3- to 4-week-old calves 

 than it is at any subsequent time. At that stage in development, the skin is 

 pigmented at least as much as it is generally in the hair seals (Phocidae) of the 

 Bering-Chukchi region and more intensely than in fur seals and sea lions 

 (Otariidae). With advancing age, the skin of the Pacific walrus becomes pro- 

 gressively paler, as does the pelage. This change is most apparent in the males, 

 whose skin and hair become so lightly pigmented in old age that some individuals 

 appear to be albinistic (Fig. 30). The pallor of such animals is most apparent 

 when they are in the water and for a short time after emergence, when the skin is 

 ischemic. After lying out on ice or land for about an hour in warm weather, they 

 become pinkish to reddish, as the skin is suffused with blood (Ray and Fay 1968). 

 This redness commonly is mistaken for "sunburn." 



About 1 % of the specimens examined had one or more small, irregular areas 

 of unpigmented skin on the flippers (Fig. 31); these were more noticeable and 

 seemed more common in fetal and newborn than in older animals. Smaller, 

 lightly pigmented to unpigmented spots were common also on the head, neck, 

 and body of most of the specimens examined, but these seemed to be only scars 



