44 CONTROLLED NATURAL SELECTION 
Fig. 1 is a pictorial representation of this 
conception; E,, E,, E,, &c., are the factors 
of the environment, shaded, to show their 
serial nature ; the area enclosed by dark lines 
is the environment of the species. Fig. 2 is 
a simplified illustration. The environment of 
MEE ET 
Fig. 2. 
a species can be classified into common and 
specific. The common environment is shared 
with other species (many animals breathe air 
and drink water) ; its specific environment it 
occupies, solus. 
If, as has been considered, structure means 
