243 



CHAPTER XXXV. 



RODENTS continued — HYSTRICID.E CAPYBARA — CA^'IES CHI^-CHILLAS OCTODONS ECHIMYINA 



AGOUTIS PORCUPINES. 



The Hystricid.^ (Map 72) take their name from the Porcinjines ; but by much the larger 

 portion of them is composed of other ingredients. Besides "the Porcupines, the family contains the 

 Cavies or Guinea-Pigs, the Chinchillas, the Chilian Squirrels or Octodons, the Spiny Eats or 

 Echimjdna, and the Pacas and Agoutis, or Dasji^roctidac. All these are South-American forms ; and, 

 with the exception of the Porcupines, so entirely so, that only two species belonging to them are 

 found anywhere else than in the New World, and only five or six out of South America. The Por- 

 cupines are different. They are found in all the four quarters of the world, but are divided into 

 two well-marked groups ; one pecidiar to the New World, and the other to the Old. 



Cavies. (Cavini.) (Map 73.) I take the Cavies first, and first of the fiimily I take the 

 puzzling Capybara as having most afiinity to the Toxodon. This animal may be called a Pachyder- 

 matous Rodent. Even its outward appearance indicates this double relationship. When viewed 

 at a distance, from its manner of walking as well as from its colour, it resembles a pig ; when 

 seated on its haunches, and attentively watching any object with one eye, it reassumes the 

 appearance of its congeners, Cavies and Rabbits.* It has, more of the Pachyderm in its con- 

 stitution, however, than merely a resemblance to a pig. It has the body of its molar teeth com- 

 pletely traversed by nine or ten plates of enamel, reminding us of the plates of which the Elephant's 

 tooth is composed, and which also are united by cement somewhat in a similar manner. Other 

 analogies with the Pachyderms, even in their habits, can be traced, indicating a certain amount 

 of connexion between the two orders. For example, when the animal is swimming in the water, 

 and has young ones, they are said to sit on its back, as the young of the Hippopotamus do on 

 its back. 



Aprojjos to this species, Mr. Waterhouse says, " As in the class Mammalia, the largest 

 known species are aquatic, so in the minor divisions of the class we find, as a general rule, the 

 the largest species have aquatic habits. Few species of the order Rodentia attain a size approaching 

 to that of the Beaver or Coj-pu, whilst in the Capybara we have presented to us by far the largest 

 species of the group, — a gigantic Water Cavy."J If Waterhouse had thought of the Toxodon 

 as a Rodent he would have had a still stronger case in point. 



But although the sjiecidation is ingenious, and receives support from some cases, on a view 

 of the whole class it applies in too few instances to allow us to regard it as a normal law 



* DAmviN, " Journal of a Naturalist," p. 50. 

 + Waterhouse, op. cit. 



