544 MANUAL OF ZOOLOGY. 



hairs. They have four molars on each side of each jaw, and 

 they possess imperfect clavicles. 



The true Porcupines (Hystrix) have non-prehensile tails, 

 which are mostly furnished with long hollow spines, but some- 

 times with scales and bristles. They are found in both the 

 Old and New World, but the American species differ in several 

 respects from those of the eastern hemisphere. They are all 

 inhabitants of hot climates, with the exception of the common 

 Porcupine (H. cristata) which occurs in southern Europe and 

 in the north of Africa. 



The nearly-allied genus Cercolabes is South American, and 

 it is distinguished from the preceding by the possession of a 

 long prehensile tail. In fact, Cercolabes, like so many of the 

 inhabitants of this wonderful continent, is adapted for an arbo- 

 real life, instead of being confined to the ground. 



Fam. 4. Castoridce. The best-known example of this family 

 is the Beaver ( Castor fiber). The distinctive peculiarities of the 

 family are the possession of distinct clavicles, the possession of 

 five toes to each foot, and the fact that the hinder feet are 

 webbed, adapting the animal to a semi-aquatic life. 



The Beaver is a large Rodent, attaining a length of from 

 two and a half to three feet. Naturally it is a social animal, 

 living in societies, and this is still the case in America ; but in 

 northern Europe and Asia, where the animal has been much 

 hunted, it leads a s61itary life. When living in social commu- 

 nities the beavers build dams across the rivers, as well as habita- 

 tions for themselves, by gnawing across the branches of trees or 

 shrubs, and weaving them together, the whole being afterwards 

 plastered with mud. In this last operation the tail, which is flat- 

 tened and scaly, is employed very much as a mason uses his 

 trowel. There is no doubt but that the Beaver shows extra- 

 ordinary ingenuity in these and similar operations ; but there 

 can be equally little doubt as to the greatly-exaggerated stories 

 which have been set afloat in this connection. The Beaver is 

 hunted chiefly for the sake of the skin, but also for the substance 

 known as castoreum. This is a fatty substance, secreted by 

 peculiar glands, and employed as a therapeutic agent. 



There are two other members of the Castoridce which are 

 likewise largely captured for the sake of their skins. One of 

 these is the Musquash (Fiber Zibethicus\ which inhabits North 

 America, and the other is the Coypu (Myopotamns coypus\ 

 which inhabits burrows in the banks of rivers in Chili. It is 

 distinguished from the true Beaver by having a hairy and not 

 a scaly tail. 



Fam. 5. Muridce. The fifth family of Rodents is that of 



