58 



NORTH AMERICAN FAUNA 74 



Postnatal Molt of Calves 



Data presented by Nikulin (1941; Table from inspection of 53 calves 

 indicated that shedding and replacement of the natal coat takes place in June and 

 July, about 1 to 2 months after birth. Information and materials obtained in the 

 present study confirm that observ ation. 



No outward signs of shedding or newly emerging hair were seen in more than 

 100 calves examined during May; histological sections of skin from a few of these 

 showed only resting follicles. In one specimen, about 2 weeks old. a few hair 

 bulbs were somewhat enlarged and descendant but lacked the intenseh" pig- 

 mented hair cones t\"pical of anagen; the stratum corneum still was compact 

 (Fig. 39a). In a second specimen, about 1 month old. hair cones were present, 

 and the stratum corneum was greatly expanded and loose (Fig. 39b). However, 

 the natal pelage of this animal still was firmly anchored, and there were no 

 outward signs of depilation. Of 10 cah es taken in early June. 3 showed bald 

 areas on the crown and midline of the back; the natal hairs adjacent to those 

 areas were loose and club-rooted. Incisions in the skin of one of those specimens, 

 taken 2 June, disclosed intensely pigmented hair shafts of the not yet emergent 

 third pelage and a loose, easily detachable cornified layer. In the remainder of 

 this group, there were no bald areas, and the natal hair still was relatively firm. 



Samples of skin from the body of four calves taken on 27 July indicated that 

 the animals were about midway through their postnatal molt. Most of the natal 

 hair already had been shed, and the remainder was loose and easily pulled out. 

 New hairs of the third pelage extended 0.5 to 2 mm abo\ e the surface of the skin, 

 and the intensely pigmented hair cones were still open and acti\"el\- growing. The 

 thick, cornified la\'er of the epidermis was intact in some areas, though loose and 

 easily rubbed off (Fig. 39c); elsewhere, its outer portion, about 0.2 mm thick, 

 already had been shed (Fig. 39d). This material was detaching as flakes. 1 to 

 3 mm in diameter. 



The date of completion of the postnatal molt is unknown. From the specimens 

 described above. I presume that the new hairs do not become club-rooted earlier 

 than mid-August to late August and that they probably do not attain their full 

 emergence above the skin before the end of that month. Chapskii (1936) reported 

 that the calves he saw in August to October had a short, fine pelage, but no 

 measured lengths \\'ere given. Mansfield (1958a) observed that the pelage of 

 calves taken in '"summer and fall" in northern Hudson Ba\' was only 1 to 2 mm 

 long. 



The progress of the postnatal molt in 13 cah es reared in capti\ it\- in North 

 American zoological gardens was followed on the basis of external appearances 

 and reported to me (personal communication) by D. H. Brown (Marineland of 

 the Pacific), W. P. Heuschele (San Diego Zoo), and G. C. Ray (New York 

 Aquarium). First indications of shedding of the natal coat were noted between 2 

 and 14 June; the first appearance of new hair was recognized between 11 June 

 and 7 July, and the new (third) pelage \ya.s regarded as full)- de\"eloped by 19 to 

 26 July. These reports indicate that the postnatal molt takes place more rapidly 

 in captives at mid-latitudes than in free-li\1ng calves under arctic conditions. 



The pre\1ously accepted notion that the natal coat of the walrus was its first 

 pelage (see Nikulin 1941; Brooks 1954; Mansfield 1958a) was questioned b}- 

 Scheffer (1958:11). who suggested that the natal coat was the "dark second 



