Taylor : doMinancy iK naturk. 
11 
occupying South America and also probably contributing its quota 
to the life of the islands and continent of Antarctica. Direct access 
to the great plains of Eastern North America being cut off by the lofty 
Rocky Mountains and other important ranges, an entry thereto is 
made by a portion of the migrants by way of Yucatan and Florida, 
and they also occupy the West Indian Islands, which were formerly 
more or less connected together. Those entering Florida became 
diffused over the Eastern United tStates, the weakest races being 
eventually driven to occupy the Central or Missourian region. 
Fig. 5.— Map showing the approximate routes traversed by the //^//czV/i:^' and other organisms 
by which life has probably overspread the earth from the assumed evolutionary area. 
The stronger waves represent the main courses of the migratory streams, the closer rippling 
indicates the relative slowness of the advance. 
Another important route is travelled by those species which have 
occupied the Eastern Mediterranean region and have crossed into 
Asia Minor, spreading towards the east by way of Afghanistan and 
Persia and only a few reaching India. 
Others from Asia Minor entered North-east Africa, passiuir along 
its northern coasts or up the valley of the Nile to the south of 
the Sahara desert and opening up the whole African continent to 
colonization. Other routes directly connecting Europe with Africa 
formerly existed and would also contribute in the diffusion of 
European life. 
A north-western route, formerly connected Europe with North 
America by a Tertiary bridge, but its apparently short duration 
prevented any but northern species taking advantage of it and the 
comparatively modern date of its existence has prevented an extended 
diffusion of some of the plants, mollusks, earthworms, etc., assumed 
to have reached America in this way. 
Although climatic barriers are generally considered one of the chief 
factors in limiting distribution this cause is not uearly so effective as 
is usually supposed, and although any immediate transference, 
