476 



ZOOLOGY 



SECT. 



PP 



Modifications of the hairs are often found in certain parts. Such 

 modified hairs are the elongated hairs of the tails of some Mammals, 

 e.g., most Ungulates ; the eye-lashes of the eye-lids, which are 

 stronger than the ordinary hairs ; and sensitive hairs or vibrissce 

 about the snout. In some Mammals the hairs in part assume the 

 form of spines, viz., in Echidna, the Hedgehogs, and the Porcupines. 

 The coating of hairs is scanty in some Mammals, and is virtually 

 absent in the Cetacea and Sirenia. In such cases the skin is greatly 



thickened, as in the 

 Elephants, &c. ; or, as 

 in the Cetacea, an un- 

 derlying layer of fat 

 performs the function 

 of the hair as a heat- 

 preserving covering. 



In Manis (Fig. 1126) 

 the greater part of the 

 surface is covered with 

 large, rounded, over- 

 lapping horny scales of 

 epidermal origin, simi- 

 lar in their mode of 

 development to those 

 of Reptiles. A similar 

 phenomenon is seen in 

 the integument of the 

 tail of Anomalurus a 

 Flying Rodent. The 

 Armadillo (Fig. 1125) 

 is the only Mammal 

 in which there occurs a 



FIG. 1113. Four diagrams of stages in the development of a 

 hair. A, earliest stage in one of those Mammals in which 

 the dermal papilla appears first ; B, C, D, three stages in Knnir Hevmnl t>vrKiTf>10tnivt 

 the development of the hair in the human embryo bib. . n y <*M mat eXOSKei&On 

 hair-bulb ; cm. horny layer of the epidermis ; foil, hair- (vide infra). 

 follicle ; grm. hair-germ ; h. extremity of hair projecting on 

 the surface in D ; muc. Malpighian layer of epidermis ; -pp. 

 dermal papilla ; seb. developing sebaceous glands ; sh.l, sh.2, 

 inner and outer root-sheaths. (After Hertwig.) 



Also epidermal in 

 their origin are the 

 horny structures in the 

 form of nails, claws, or hoofs, with which the terminations of the 

 digits are provided in all the Mammalia except the Cetacea. And 

 the same holds good of the horny portion of the horns of Ruminants. 

 The horns of the Rhinoceros are also epidermal, and have the 

 appearance of being formed by the agglutination of a number of 

 hair-like horny fibres. 



Cutaneous glands are very general in the Mammalia, the most 

 constant being the sebaceous glands (Figs. 1111, D ; 1112, HBD), 

 which open into the hair-follicles, and the sweat glands (Fig. 1111, 

 SD). In many Mammals there are, in addition, in various parts of 

 the body, aggregations of special glands secreting an odorous matter. 



