GENERAL CHARACTERISTICS. 
i3 
by their means alone that we are able to explain several apparent anomalies in the 
geographical distribution of living groups. How, for instance, could we possibly 
explain the present existence of tapirs only in such widely remote areas as the 
Malay Peninsula and Islands and South America, unless we had learnt by geological 
explorations that these animals formerly roamed over large portions of Europe 
and Asia, from whence their descendants gradually migrated to the regions where 
they now remain ? 
The former occurrence of an epoch of great cold in the northern hemisphere 
known as the Glacial period, furnishes us with an explanation of how nearly related 
animals are now confined to isolated mountain chains; their ancestors having been 
enabled, during the prevalence of the cold, to spread over the plains of the temperate 
regions, from whence they retreated with the advent of warmer conditions to seek 
a congenial climate in the nearest mountain region. 
Orders of Mammals may be divided into eleven main groups or orders, 
Mammals. which may be arranged as follows, and will be treated of in the same 
sequence, viz.:— 
1. Apes, Monkeys, and Lemurs— Primates. 
2. Bats— Chiroptera. 
3. Insectivores— Insectivora. 
4. Carnivores— Carnivora. 
5. Hoofed Mammals— Ungulata. 
6. Manatis and Dugongs— Sirenia. 
7. Whales and Porpoises— Cetacea. 
8. Rodents— Rodentia. 
9. Sloths, Anteaters, etc.— Edentata. 
10. Pouched Mammals—M arsupialia. 
11. Egg-laying Mammals— Monotremata. 
It is not to be supposed that all these groups are separated from one another 
by differences of equal importance. For instance, No. 10 differs from the preceding 
groups by characters of far more importance than do any of those nine from one 
another; while the members of No. 11 differ fundamentally, not only from the first 
nine groups, but almost equally markedly from No. 10. 
Having said thus much by way of introduction, we proceed to the considera¬ 
tion of the first order of Mammals. 
