62O MANUAL OF ZOOLOGY. 



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

 real life, instead of being confined to the ground. 



Fam. 4. Castorida. 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 posses- 

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

 are mostly 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 solitary life. When living in social commu- 

 : nities the beavers build dams across the rivers, as well as habi- 

 tations for themselves, by gnawing across the branches of trees 

 or shrubs, and weaving them together, the whole being after- 

 wards plastered with mud. In this last operation the tail, which 

 is flattened and scaly, is employed very much as a mason uses 

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

 traordinary 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 sub- 

 stance known as castor eum. 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 (Myopotamus coy pus), 

 which inhabits burrows in the banks of rivers in Chili. In the 

 Musquash the hind-feet are not completely webbed, and the 

 tail is moderate in size, and covered with short hairs and small 

 rounded scales. In the Coypu the hind-feet are webbed, but 

 the tail is long, rounded, and furnished with scales and scat- 

 tered hairs. 



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

 the MuridcB) comprising the Rats, Mice, and Lemmings. In 

 this family the tail is long, always thinly haired, sometimes 

 naked and scaly. The lower incisors are narrow and pointed, 

 and there are complete clavicles. The hind-feet are furnished 

 with five toes, the fore-feet with four, together with a rudi- 

 mentary pollex. 



The Rats (Mus rattus and Mus decumanus\ the common 

 Mouse (Mus musculus\ the Field-mouse (Mus sylvaticus), and 

 the Harvest-mouse (Musmessorius), are all well-known examples 

 of this family, and are too familiar to require any description. 



