PORCUPINES AND SPINY MICE. 39 



terminate in a brush of flattened spines, and are thus 

 evidently less specialized ci'eatures. 



America is tenanted by a group of porcupines easily 

 distinguished from their Old World cousins by having 

 the soles of their feet covered with rough tubercles, instead 

 of being perfectly smooth, and also by their comparatively 

 short spines being mingled with a number of long hairs, 

 by which they may be partially concealed. The Canada 

 porcupine (Erethizori} differs from all the other American 

 species in having a short stumpy tail, and also in its non- 

 arboreal habits ; its spines being almost hidden by the 

 hairs. In parts of North America these porcupines are so 

 abundant as to be a positive nuisance, and an enterprising 

 engineer, with true American " cuteness," hit upon the 

 original idea of utilizing their bodies as fuel for his engine 

 apparently with the most satisfactory results. The 

 lighter-built tree-porcupines (Synetheres), which are mainly 

 characteristic of the southern half of the American conti- 

 nent, are easily distinguished by their long tails, which, 

 as in so many South American mammals, are prehensile. 

 These porcupines are thoroughly arboreal in their habits, 

 and it is therefore easy to understand why their spines 

 are so much shorter than those of their terrestrial Old 

 World cousins, who have to rely solely on these weapons 

 for their protection. 



In addition to the members of the porcupine family, 

 there are several other groups of rodents which develop 

 a more or less complete coating of spines. Among the 

 most remarkable of these groups are the spiny mice 

 (Acomys) of Syria and Eastern Africa, one of which, when 

 it has its spines erected, is almost indistinguishable at the 

 first glance from a diminutive hedghog. The spiny rat 

 of Celebes (Echinothrix) is another member of the mouse 

 family having the fur thickly intermingled with spines. 

 In a third rodent family (Octodontidse), nearly all the 

 members of which are South American, there is also a 

 genus (Echinomys}, taking its name from the number of 

 flattened spines mingled with the fur of the back charac- 

 terizing all its representatives. It will thus be obvious 

 that even in a single mammalian order we have several 



