8 GENERAL ANATOMICAL CHARACTERS 
In a large number of mammals hairs of one kind only are 
scattered pretty evenly over the surface ; but in many there are two 
kinds, one longer, stiffer, and alone appearing on the surface, and 
the other shorter, finer, and softer, constituting the under fur, 
analogous to the down of birds. This under fur, or pashm as it is 
called by the natives of Kashmir, is especially abundant in the 
mammals inhabiting the cold plateau of Tibet and the adjacent 
regions. In many cases hairs of a different character from those of 
the general surface grow in special regions, forming ridges or tufts 
on the median dorsal or ventral surface or elsewhere. The tail is 
very often completed in this way by variously disposed elongated 
hairs. The margins of the eyelids are almost always furnished with 
a special row of stiffish hairs, called cilia or eyelashes ; and in most 
mammals specially modified hairs, constituting the vibrisse or 
whiskers, and endowed, through the abundant nerve supply of their 
basal papillae, with special tactile powers, grow from the lips and 
cheeks. In some mammals the hairy covering is partial and limited 
to particular regions ; in others, as the Hippopotamus and the Sirenia, 
though scattered over the whole surface, it is extremely short and 
scanty ; but in none is it reduced to so great an extent as in the 
Cetacea, in which it is limited to a few small bristles confined to the 
neighbourhood of the lips and nostrils, and often only present in 
the young or even foetal condition. 
Some kinds of hairs, as those of the mane and tail of the Horse, 
appear to persist throughout the life-time of the animal; but more 
generally, as in the case of the body hair of the same animal, they 
are shed and renewed periodically, generally annually. Many 
mammals have a longer hairy coat in winter, which is shed as 
summer comes on; and some few, which inhabit countries covered 
in winter with snow, as the Arctic Fox, Variable Hare, and Ermine, 
undergo a complete change of colour in the two seasons, being 
white in winter, and gray or brown in summer. The several species 
of Cape Mole (Chrysochloris), the Desmans or Water Moles (Myogale), 
and Potamogale velot, are remarkable as being the only mammals 
whose hair reflects those iridescent tints so common in the feathers 
of tropical birds. 
The principal and most obvious purpose of the hairy covering is 
to protect the skin against external influences, especially cold and 
damp. Its function in the hairless Cetacea is supplied by the 
specially modified and thickened layer of adipose tissue beneath the 
skin, called “ blubber.” 
Colour.—From the consideration of hair we are easily led to 
that of colour. As a general rule, bright and primary colours are 
absent in the class ; but among the Baboons we find brilliant patches 
of scarlet or blue on some of the bare portions of the body, and one 
of the South American Monkeys (Brachyurus) has its whole face of 
