CHAPTER XXIII. 
SUMMARY OF THE DISTRIBUTION, AND LINES OF MIGRATION, OF 
THE SEVERAL CLASSES OF ANIMALS. 
Having already given summaries of the distribution of the 
several orders, and of some of the classes of land animals, we 
propose here to make a few general remarks on the special 
phenomena presented by the more important groups, and to 
indicate where possible, the general lines of migration by which 
they have become dispersed over wide areas. 
Mammalia. 
This class is very important, and its past history is much 
better known than that of most others. We shall therefore 
briefly summarise the results we have arrived at from our ex- 
amination of the distribution of extinct and living forms of 
each order. 
Primates . — This order, being pre-eminently a tropical one, 
became separated into two portions, inhabiting the Eastern and 
Western Hemispheres respectively, at a very early epoch. In 
consequence of this separation it has diverged more radically 
than most other orders, so that the two American families, Cebidse 
and Hapalidee, are widely differentiated from the Apes, Monkeys, 
and Lemurs of the Old World. The Lemurs were probably still 
more ancient, but being much lower in organisation, they 
became extinct in most of the areas where the higher forms of 
Primates became developed. Remains found in the Eocene 
formation indicate, that the North American and European 
