RODENTS 8l 



enemy, it gives a shrill warning whistle, and in a trice the whole flock 

 has vanished into the summer holes (which are less deep) or underneath 

 rocks. Its teeth are of the usual rodent type, and enable it to cut off 

 even- the shortest grass, some of which it dries to hay ae a padding for 

 its winter dwelling. With the advent of winter the animals in families 

 retire to their holes. To prevent the entrance to the chamber of the 

 death-chilling cold, the passage, 25 to 30 feet long, which leads to it, is 

 closely and firmly walled up from within with stones, earth and hay to a 

 length of from 3 to 7 feet. The air in the chamber is consequently not 

 cooled down to below 10° to 12° C. (50° to 53° P.). The members of the 

 family then lie close to each other in the soft hay, and soon all are 

 buried in deep sleep. 



Family 2: Beavers (Castoridae). 



The European Beaver (Castor fiber) . 



(Body up to 2 feet 8 inches long ; tail 1 foot.) 



Formerly the beaver used to inhabit all the wooded banks of the lakes 

 and rivers of Europe. Incessant pursuit, however, for the sake of its 

 valuable fur, its excellent flesh, and the grease, or castoreum, a fatty, 

 salve-like substance secreted by two anal glands, has long ago exter- 

 minated it in Britain and many parts of the Continent. At present it is 

 found in small numbers on the Elbe and its tributaries, between Witten- 

 berg and Magdeburg. In Bussia, Scandinavia, Siberia and North America 

 also a war of purposeless extermination is being waged against this 

 animal, which will, in all probability, soon have to be numbered among 

 the ' ( creatures of the past." The beaver is as much at home in the 

 water as below or on the earth, and the structure of the body is in 

 accordance with its varied habits. 



A. The Beaver as a Water-Animal. 



I. It is provided against a fatal cooling of the body, through too long 

 a stay in the water, by the same means as the otter (which see). 



II. The structural characters, which enable the otter (which see) to 

 swim for protracted periods and to dive with skill, are for the most part 

 repeated in the case of the beaver. 



(a) Compare what has been said in the case of the otter with regard 

 to air-spaces between the hairs of the fur, the lubrication of the latter, 

 the general form of the body, the importance of the tail, the shortness 

 of the legs, the closure of mouth and nose. 



(b) The beaver is not nearly so rapid a swimmer as the otter, its body 



6 



