COLOURS AND PATTERNS OF MAMMALS 83 



surface clean. Sometimes this process is slow and continuous; 

 as in ourselves, sometimes it takes place at regular intervals, in 

 large sheets which may extend to the whole body, as when a serpent 

 sloughs, casting off the complete outer layer of the skin, even to the 

 transparent membrane of the eye. 



The warm coats of fur or feathers which protect the bodies of 

 most mammals and birds are formed chiefly of the outer horny 

 layers of the skin, and, within certain limits, can be cast off and 

 renewed. This process of moulting is useful in many ways. It 

 gives the opportunity of replacing coats that have become worn 

 and faded, by coats that are bright and clean. It gives the oppor- 

 tunity for a change of clothing from the warm covering necessary 

 in winter to the lighter covering which is more healthy in warm 

 weather, and perhaps most important of all, it makes possible 

 periodical changes in colour and pattern. Just as when the outer 

 layers of the skin are shed off they may be replaced by differently 

 coloured layers, so the old hairs or feathers, when they fall off, may 

 be replaced by hairs and feathers with different colours and patterns. 

 It is the process of moulting far more than any actual change in 

 skin, fur or feathers that underlies the differences between young 

 and old animals, or between mature animals at different seasons of 

 the year. 



Lemurs, monkeys and human beings form the most highly modified 

 group of mammals, the group that is furthest removed from the 

 reptilian ancestors, and I do not know of any in which either the young 

 or the adults are spotted or striped, except that the tails are some- 

 times ringed. The skin is usually dark, but there may be brightly 

 coloured patches on the face and other areas not covered with hair, 

 and these, whatever their use may be, fall into the higher grades of 

 coloration and do not conform with the structural lines of the body. 

 The hair also is either uniform, or decorated with crests, ridges or 

 tufts which, like the patches on the naked skin, seem to be late 

 additions to the coloration of the body, and differ much in closely 

 allied species. Monkeys, like human beings, moreover, have lost 

 the habit of moulting regularly, and are continually shedding off 

 and renewing their hairs. The change is modified by exposure to 

 cold, and the coats of those that have access to the open air all the 

 year round become longer and thicker than those of animals housed 

 in heated apartments. And so there are no startling differences 

 between the young and the adults. Like human beings, young 

 monkeys are born with a very scanty coat of silky hair, large parts 



