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 Pakearctic 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 Lcpus 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 Muridae 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 Pakearctic 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 Paleearctic 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 
p. 2 
