354 THE HISTORY OF CREATION. 
primeval home, or its natal place. This is a necessary 
consequence of the relations of population and over-popula- 
tion (pp. 161 and 256). The more an animal or vegetable 
species increases, the less is its limited natal place sufficient 
for its sustenance, and the fiercer the struggle for life; the 
more rapid the over-population of the natal spot, the more 
it leads to emigration. These migrations are common to all 
organisms, and are the real cause of the wide distribution 
of the different species of organisms over the earth’s surface. 
Just as men leave over-crowded states, so all animals and 
plants migrate from their over-crowded primzeval homes. 
Many distinguished naturalists, especially Lyell’ and 
Schleiden, have before this repeatedly drawn attention to 
the great importance of these very interesting migrations of 
organisms. The means of transport by which they are 
effected are extremely varied. Darwin has discussed these 
most excellently in the eleventh and twelfth chapters of 
his work, which are exclusively devoted to “geographical 
distribution.” The means of transport are partly active, 
partly passive; that is to say, the organism effects its 
migration partly by free locomotion due to its own activity, 
and partly by the movements of other natural bodies in 
which it has no active share. 
It is self-evident that active migrations play the chief 
part in animals able to move freely The more freely an 
animal’s organization permits it to allmovein directions, the 
more easily the animal species can migrate, and the more 
rapidly it will spread over the earth. Flying animals are of 
course most favoured in this respect,among vertebrate animals 
especially birds, and among articulated animals, insects. 
These two classes, as soon as they came into existence, can 
