ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



49 



tissue only in their distal, most exposed parts (personal observations). The real 

 cause for their development remains obscure, but I believe that the hypothesis of 

 secondary' sexual development is strongest, because the bosses seem to me to have 

 possible social as well as structural value. The thick, nearly hairless neck of the 

 adult male, with its pale, "lumpy" skin contrasts markedly with the more 

 slender, browner, and smoother neck of the adult female and of immature 

 animals of either sex. Hence, it probably serves also as an important visual cue to 

 other walruses of the sex and maturity of the individual. 



Blubber 



Like other pinnipeds, the walrus has a thick layer of cutaneous fat, the 

 blubber or hypodermis. This layer varies in thickness over different parts of the 

 animal; it is thickest on the torso and thinnest on the head and appendages. 

 According to Sokolov (1960), it is thicker on the ventral than on the dorsal 

 surfaces of the torso, but his sample size was small (three specimens) and he had 

 only two or three measurements from each. His measurements (cm) were as 

 follows: 



"Chest" 



Adult female 1 October 101 



Young male 23 September 48 



Adult male 22 September 59 



Hence, I question his conclusion. 



I measured the thickness of the blubber in a few specimens but only in one 

 location, on the sternum, midway between the forelimbs. Presumably, this 

 measurement is comparable to Sokolov 's measurements on the "chest." My goal 

 was to obtain a large enough series from all seasons of the year with which to test 

 the Eskimos' impressions that the males are fattest in winter and that the females 

 are fattest when carrying a full-term fetus. The data acquired thus far (Table 7) 

 are inconclusive. 



Epidermal Structure and Topographic Variation 



The epidermis of mammals is a stratified squamous epithelium comprising five 

 distinctive layers: germinative, spinous, granular, lucid, and cornified. In only a 

 few samples of walrus skin were all of these strata apparent. The stratum 

 lucidum often was absent; in some instances there was no definite stratum 

 granulosum; in a few specimens, the stratum germinativum was not well differ- 

 entiated. In two small areas on the ventral surface of the upper lip, I found no 

 stratum corneum. The reasons for these variations and deficiencies are unknown. 

 No relations with sex, age, or season were apparent in my small sample. 



In normal section, the epidermis of the Pacific walrus is about 1 mm thick and 

 appears wave-like, with large, primary undulations, the amplitude of which 

 often exceeds the thickness of the tissue itself; smaller, secondary irregularities 

 occur at the dermal -epidermal interface (Fig. 33). Actually, the primary waves 

 are more or less conical, conforming to the major dermal papillae; the secondary 



"Back" "Belly" 

 60 



34 36 

 39 



