IIYSTRICID.'E — CIIINCniLLAS. 245 



northward, where the country is very sterile, the animal again occurs. Its southern limit is be- 

 tween Ports Desire and St. Julian, about 48° 30'." * 



The rest of the Cavies are chiefly found in Brazil, from whence probably comes the common 

 Guinea-Pig, whether it be descended from the C. aperea, or be a distant species. Eight species are 

 met with in Brazil ; three in. Bolivia, east of the Andes ; one in Guiana ; two in Paraguay ; 

 and two, including the Dolichotis, in Patagonia. None are fomid in Chili. One, C. Cutleri of 

 Von Tschudi, is said to occur in Peru, west of the Andes ; with one other questionable exception, 

 no species of the HystriciDjE is found there. 



Dr. Giebel and other authors include the Paca and Dasj^jroctas among the Cavies. I am not 

 sure but that they may be right ; but on the whole, where I have no decided opinion of my own, I 

 prefer to follow Mr. Waterhouse's arrangement, because he has made it a special and successful 

 subject of study. 



Chinchillas. (Chinchillin.e.) (Maj) 74.) I have already expressed mj' dissent from the idea 

 of series of animals existing parallel in rank, except in so far as that implies degrees of affinity. Two 

 brothers maj^ produce families which are parallel in rank, being alike in degree of affinity, and to 

 such an extent I admit the parallelism ; but something more seems to be intended by Owen and 

 Waterhouse, and some others, who have adopted the idea, when they speak of parallel or equivalent 

 groups. They speak of them as if Nature had planned out parallel series, in which representative 

 analogies were to be found aj)plicable to the various essential characters of each. Mr. Waterhouse 

 dwells upon this in his preliminary remarks on the Marsupial order. And in this family, in 

 pointing out the affinities of the Chinchillas to their different allies, he repeats the same idea. 

 He says, " As, however, the Chinchillas and Hares are essentially of two very distinct types of the 

 Rodent structure, and the characters just alluded to (imperfect palate, &c.) are for the most part 

 characters indicative of a low grade of organization, it would seem that the amount of resemblance 

 which exists between these two groups, the Cavies and the Hares, rather arises from these lowest 

 members of the Hystricida; being nearly parallel in rank, in the animal scale, with the LeporidaD, 

 and does not indicate an affinity of a very near degree."t It rather apjjcars to me that, as in 

 the resemblances between cousins, such parallelisms are an indication of no distant affinity, at all 

 events certainly involve no general or special law other than that which produces similarity of form 

 and structure by descent. The existence of such parallelism is only the evidence of a common origin. 



With the excej^tion of the Yiscacha, which inhabits the plains of the Pampas, all the 

 Chinchillas (in whole amounting to only three or four species) inhabit the Ipftj' regions of the Andes 

 of Chili, Bolivia, and Peru. The Viscacha is so stout and heavy, and resembles the light and 

 active Chinchillas so little in outward appearance, that .it has been mistaken for a Marmot. But, 

 as Mr. Waterhouse has pointed out, it is in fact a burrowing Chinchilla, in the same way that the 

 Marmot is a burrowing Squirrel. In all essential points of structure it is formed on the same model. 

 Mr. Darwin says that it is found as far south as the Rio Negro, in hit. 41° S. L. but not beyond. It 

 cannot, like the Dolichotis Patagonica, subsist on the gravelly and desert plains of Patagonia, 

 but prefers a clayey or sandy soil, which produces a different and more abundant vegetation. 

 Near Meudoza, at the foot of the CordQlera, it occurs in close neighbourhood -with the allied 



* Darwin, " Zoology of H.M.S. Beagle," and "Journal of a Naturalist," p. 70. 

 t Waterhouse, op. cit. ii. 209. 



