128 



YERTEBRATA I MAMMALIA. 



all the Rodents on account of their spines, which serve 

 them for a defensive armor. These spines lie flat upon 

 the bodj when the animal is at rest, but are raised when 

 the animal is excited. Our species have spines only a few 



FIG. 148. 



Crested Porcupine, Hystriz cristata, Linnaeus. 



inches m length, but a species (Fig. 148) of Southern 

 Europe has very long spines, some of which attain a foot 

 in length. Porcupines have a total length of about two 

 and a half feet. 



All of the families of Rodents thus far noticed to- 

 gether with the Agoutis or Dasyproctidse, the Capybaras 

 or Hydroehceridjfi, and the Chinchillas or Chinchillidce, 

 all of South America have only two incisors in the upper 

 jaw and two in the lower. 



But the little hare-like animals called Pikas or Lagomy- 

 idse of the northern regions, and the Rabbits and Hares or 

 Leporidte of all parts of the world, differ from all other 



