6 MAMMALS. 



a small one from Madagascar, belonging to the Insectivorous order, and named 

 Microgale, in which the tail is nearly three times as long as the body. In some 

 of the apes and monkeys the tail is absent ; and it is very short in the bears among 

 the Carnivores, and in many deer among the Hoofed Mammals, or Ungulates, In 

 many Ungulates, however, such as cattle, it is of great length ; and in that group 

 it has its extremity furnished with a tuft of hair, and thus forms an effectual 

 instrument for brushing away flies from the body. In the spider -monkeys of 

 South America, as well as in the opossums and phalangers, in certain porcupines, 

 and other forms, the tail is prehensile, and thus serves as an important aid in 

 climbing, or to suspend its owner's head downwards. In the beaver the tail is 

 expanded into a flattened oar-like form, which probably acts as a rudder in swim- 

 ming. But the most remarkable modification of this useful organ occurs in the 

 whales and dolphins, when it is expanded into a large forked structure, termed 

 by whalers ' flukes,' and is the main organ in propelling the bo'dy through the 

 water. 



External In regard to the external covering, we have already said that hairs 



Covering. are always present on some portion of the body during some period 

 of life. In the whales these hairs may, however, be reduced to a few bristles in 

 the region of the mouth, which disappear when the animal attains maturity. 

 Mammals never develop that modified kind of hair-structure known as feathers, 

 which are peculiar to Birds. The body may, however, be covered with overlapping 

 scales, like those so common in Reptiles, but this occurs only in the pangolins, or 

 scaly ant-eaters of India and Africa. The tail of the common rat is an example 

 of a part of the body covered with scales, having their edges in apposition ; but in 

 both these instances hairs are mingled with the scales. Still rarer than scales are 

 bony plates, developed in the true skin. At the present day these structures are 

 only met with among the well-known armadillos of South America, which are 

 furnished with bucklers and transverse bands of these bony plates, and are in some 

 cases able to roll themselves up into a ball, presenting on all sides an impenetrable 

 coat of mail. In the Pleistocene, or latest geological period before the present, 

 South America produced, however, a number of huge Mammals allied to the 

 armadillos, and Known as glyptodonts, which were covered with a continuous 

 cuirass of bony plates, reaching in some cases more than an inch in thickness. 

 That these huge and well-armoured forms, which one might regard as typical 

 examples of animals fitted to withstand all enemies, have perished, while their 

 smaller and less completely defended allies have lived on, show us that there are 

 other causes at work than the attacks of foes in the destruction of animals. 

 Between the plates of the armour of the armadillos hairs are always developed, 

 and in one species these are so abundant as to completely hide the plates themselves, 

 and render the general appearance that of an ordinary hairy mammal. 



The use of hair is mainly to protect the body from cold, and thus to aid in the 

 maintenance of a uniform high temperature ; and when hairs are absent, we find 

 this function performed by a more or less thick fatty layer beneath the skin, which, 

 when it is excessively developed, as in the whales, is known as blubber. To com- 

 pensate for the difference between the temperature of winter and summer, many 

 Mammals which inhabit the colder regions of the globe develop a much thicker 



