RODENTIA. 83 



Hedgehogs has bristles instead of hair, and the skin 

 of the back is furnished with such muscles that the ani- 

 nal, by bending his head and paws towards his abdo- 

 men, can shut himself up as in a bag, and present bris- 

 tles on all sides to the enemy. 



The European Hedgehog, E. europceus, Buff. , inhabits 

 woods and hedges, passes the winter in its burrow, and 

 feeds upon insects and fruit. 



The Genus Centetes Tenrecs has the body covered 

 with spines or bristles like Fi s- ? 2 - 



the hedgehog ; but the ani- 

 mals of this genus have not 

 the power of rolling them- 

 selves so completely into a 

 ball. Three species inhab- 

 it Madagascar. They pass Tenrec > c - ***i-**i****> 

 three months of the year in a state of. lethargy, although 

 inhabiting the torrid zone. 



In the cool and cold regions there are many animals 

 that pass into a torpid condition during the coldest part 



of the year, the season least favorable for securing food. And while in this state their 

 physiological conditions seem to approximate those of cold-blooded animals. The Hedge- 

 hog and Bat fall into so deep a torpor that no sign of breathing can be detected ; and in 

 the Bat's heart the pulsations fall from 200 in a minute to 30 in a minute, during torpidity. 



SUB-SECTION VII. 



THE ORDER OF RODENTIA, OR GNAWERS. 



The Order of Rodentia comprises all the gnawing 

 Mammalia They are readily distinguished by their 

 teeth. In each jaw they have two chisel-shaped inci- 

 sors, between which and the molars there is a wide space 

 without teeth. The incisors are covered with enamel 

 only in front, so that their posterior edges wear away 

 faster than the anterior edges, thus always keeping these 

 teeth sharp, however much they are used ; and they 



