CHAP. XVII.] MAMMALIA. 243 



and Guatemala. In the Nearctic region, they are most abundant 

 in the central and western parts of the continent, and they ex- 

 tend to the Arctic Ocean and to Greenland. They are found in 

 every part of the Palsearctic region, from Ireland to Japan ; three 

 species range over all India to Ceylon, and others occur in 

 Hainan, Formosa, South China, and the mountains of Pegu ; the 

 Ethiopian region has only four or five species, mostly in the 

 southern extremity and along the East coast. An Indian species 

 is now wild in some parts of Java, but it has probably been in- 

 troduced. 



Extinct Leporidce. — Species of Zcpus occur in the Post-Plio- 

 cene and Newer Pliocene of France; but only in the Post- 

 Pliocene of North America, and the caves of Brazil. 



General Remarks on the Distribution of the Rodentia. 

 With the exception of the Australian region and Madagascar, 

 where Muridse alone have been found, this order is one of the most 

 universally and evenly distributed over the entire globe. Of the 

 sixteen families which compose it, the Palsearctic region has 10 ; 

 the Ethiopian, Nearctic, and Neotropical, each 9 ; and the Orien- 

 tal only 5. These figures are very curious and suggestive. We 

 know that the rodentia are exceedingly ancient, since some of 

 the living genera date back to the Eocene period ; and some an- 

 cestral types might thus have reached the remote South Ameri- 

 can and South African lands at the time of one of their earliest 

 unions with the northern continents. In both these countries 

 the rodents diverged into many special forms, and being small 

 animals easily able to conceal themselves, have largely survived 

 the introduction of higher Mammalia. In the Palsearctic and 

 Nearctic regions, their small size and faculty of hibernation may 

 have enabled them to maintain themselves during those great 

 physical changes which resulted in the extermination or banish- 

 ment of so many of the larger and more highly organised Mam- 

 malia, to which, in these regions, they now bear a somewhat 

 inordinate proportion. The reasons why they are now less 

 numerous and varied in the Oriental region, may be of two 

 kinds. The comparatively small area of that region and its 



