534 MAMMALS. 



the lifetime of the animal, thus most young deer have spots, but only 

 the Fallow and Axis deer retain these when adult. To an excess of 

 pigment is due the variation known as melanism or blackness, e.g. , in 

 black wolves and rabbits ; to a dearth of pigment albinism is due, as in 

 white mice and white elephants. In tropical countries the skin is some- 

 times very darkly coloured, as in Indian cattle, and many monkeys — 

 especially males— are notable for the bright colours of the bare parts of 

 the body. 



Among other tegumentary structures are the scales which 

 occur along with hairs on the pangolins {Manis), the scales 

 on the tails of rats and beavers and some other forms ; the 

 thickened skin-pads or callosities on the ischia of apes, the 

 breast of camels, the legs of horses ; the nails, claws, or hoofs 

 which ensheathe the ends of the digits in all mammals except 

 Cetaceans. Unique is the armature of the armadillos, for it 

 consists of bony plates developed in the dermis, overlaid by 

 epidermic scales. The median solid horns of the rhinoceros 

 are epidermic outgrowths, comparable to exaggerated warts ; 

 the paired horns of the Ruminants consist of epidermic 

 sheaths covering outgrowths of the frontal bones, but extend- 

 ing far beyond these ; the antlers of stags are outgrowths of 

 the frontal bones, and, except in the reindeer, are cast and 

 regrown each year, and possessed by the males only. 



The skin of Mammals, unlike that of Birds, is rich in 

 glands. Sebaceous glands are always associated with the 

 hair-follicles, and sudorific or sweat glands are scattered 

 over the skin. 



Specialised glands are also very common, especially those which 

 secrete some strongly odoriferous stuff, scenting which the animals 

 recognise their fellows, their foes, and their prey. Often they are most 

 developed in ths males, and their activity increases at the pairing 

 season. 



Among the numerous special glands may be noted, those which are 

 connected with a perforated spur on the hind-legs of male Monotremes, 

 the sub-orbital glands of antelopes and deer, the anal glands of carni- 

 vores, the perineal glands of the civet, the preputial glands of the musk- 

 deer and beaver, the inter-digital glands of the sheep. 



Most characteristic, however, are the mammary glands, 

 functional in female Mammals after parturition. They seem 

 to be specialisations of sebaceous glands, except in Mono- 

 tremes, in which they are nearer the sudorific type. They 

 consist of branching tubes opening by one or several aper- 



