ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



57 



Hairs plucked from the body surface of these seven fetuses were club-rooted. 

 Histological sections from the body skin of two of the fetuses, a male taken 6 De- 

 cember and a female taken 15 December, showed pelage hair follicles in 

 retrogressive (catagen) and resting (telogen) stages, respectively. Samples of 

 meconium (fecal material) from the colon of each of these two specimens were 

 washed in tap water and examined for shed hairs. Because the meconium 

 comprises cells and other debris ingested by the fetus with the amniotic fluid, 

 hairs that are shed by the fetus also will appear there. In about 10 cm^ of this 

 material from each specimen, a total of two broken vibrissae and nine pelage 

 hairs of the type just described were found. The presence of so few shed hairs and 

 only of the types already present on the specimens indicated that the white, wavy 

 coat was the first (lanugo) pelage and that it was the product of the follicular 

 cycle whose beginning was seen in the smaller fetuses. 



The next older fetus, taken in mid-January (7 months post-implantation), had 

 a crown-rump length of 56.5 cm and was shedding its lanugo. Coarser, 

 brownish hair was present on the head, neck, chest, back, and belly and mixed 

 with the white lanugo on the flanks and shoulders. White hair of the first pelage 

 was present alone in the axillae, on the limbs, and about the umbilicus. 

 Histological sections from each of those locations showed shallow-rooted club 

 hairs of the first pelage and deeply rooted, actively growing, pigmented hairs of 

 the second pelage. Sweat and sebaceous glands were well developed, and all of 

 the sweat ducts entered the hair canals distal to the sebaceous ducts. White, 

 wavy hairs of the first pelage were abundant in the meconium. Maceration of the 

 meconium in an aqueous solution of sodium hydroxide (to remove the cellular 

 debris) yielded a dense, white felt of lanugo hairs, identical in dimensions and 

 pigmentation to those of the younger fetuses. 



I examined superficially 11 fetuses taken in late March, none of which showed 

 any outward traces of the lanugo. The hairs of their second pelage extended 2 to 

 3 mm above the surface of the skin. Histological preparations from two of these 

 fetuses, taken on 23 and 24 March, about 9.3 months post-implantation, showed 

 deeply rooted hairs of the second pelage in late catagen and early telogen. 



The last group of fetuses was obtained in April and May, at or near full-term 

 development. Ten of these were examined superficially, and three were 

 examined histologically. The hair on each fetus was straight to slightly curly, 

 nonmedullated, heavily pigmented in the distal third of the shaft, and extended 3 

 to 5 mm above the surface of the skin. In cross section, each hair was elliptical 

 near the base; in the distal two-thirds of the shaft, it was broadly lenticular; 

 distally, each hair tapered to a fine point 3 to 6 fim in diameter. Histological sec- 

 tions showed the hairs to be club-rooted and in catagenetic and telogenetic fol- 

 licles. There was no evidence of new growth or of the fine hairs of the lanugo 

 pelage. The fine hairs, however, were abundant in the meconium. 



The pelage of calves up to 1 month old was identical to that of the full-term 

 fetuses, except that it extended 1 to 2 mm farther above the surface of the skin. 

 Apparently, this increase was due only to the hairs having migrated outward 

 slightly during late telogen, after the club-root was fully formed. Each pilary 

 unit included a capacious sweat gland and several small sebaceous glands. The 

 duct of each sweat gland entered the hair canal at the same level as or slightly 

 distal to those of the sebaceous glands, as in the full-term fetuses. 



