. An introduction to zoology : for the use of high schools . r about the lips ofthe young. So the hairy covering is as characteristic for theMammalia as the hoi-ny scales are for the reptiles. Although,like scales and feathers, hairs are epideiTual structures, nourishedby a papilla of the corium, yet there is a fundamental differencebetween them in their development. Both scales and featheisbegin by a thickening of the epidermis which projects beyondthe level of the skin, and, in the case of the feather, is onlyafterwards retracted into the follicle, but the hair begins by athickening of the e
. An introduction to zoology : for the use of high schools . r about the lips ofthe young. So the hairy covering is as characteristic for theMammalia as the hoi-ny scales are for the reptiles. Although,like scales and feathers, hairs are epideiTual structures, nourishedby a papilla of the corium, yet there is a fundamental differencebetween them in their development. Both scales and featheisbegin by a thickening of the epidermis which projects beyondthe level of the skin, and, in the case of the feather, is onlyafterwards retracted into the follicle, but the hair begins by athickening of the epidermis which grows inwards into the cutis,and only afterwards comes to project beyond the level of theskin. (Fig. 100.) In the Cat two kinds of haira are present, those which con- HIGH SCHOOL ZOOLOGY. 145 stitute the fur, and tliose which form the whiskers {vih^issce);the hitter from the richness of their nerve-supply are especiallytactile in function. In many of the Carnivoi-a and otherordeiS a soft under-fur is overlaid by stronger bristle-like haii-a,. Fif,. inO—Section throujrh skin of horse—enlarged. «, epid-ermis ; b, its Malphigian layer, c, pai)illary layer of coriuni, rf;c, Subcutaneous tissue ; /, hair in its follicle, p, with papilla h ;i, old hair being replaced by k ; I, sebaceous glands; tii, sweatglands ; n, sweat duct. which form the external coat. The hairs aie lubricated ))y thesecretion of the sebaceous glands, which open into the necks ofthe hair-follicles. The skin of the Mammal is therefore aicherin glands than is that of the Reptiles or Birds. In additionto these, however, there are also sweat glands, which selectfrom the blood certain materials which have to be excretedfrom it, and so the skin of the Mammal comes to be an im-portant excretory organ. Aquatic Mammals alone are desti-tute of these glands. Of the two kinds of glands referred to,it is the sebaceous kind which the milk-glands resemble mostas to structure. 146 HIGH SCHOOL ZOOLOGY. 5. In
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1889
