‘ 
INDEFINITELY FROM THE ORIGINAL TYPE. 43 
because it would make itself felt at the very first 
step, by rendering existence difficult and extinction 
almost sure soon to follow. An origin such as is 
‘here advocated will also agree with the peculiar 
character of the modifications of form and structure 
which obtain in organized beings—the many lines 
of divergence from a central type, the increasing 
efficiency and power of a particular organ through 
a succession of allied species, and the remarkable 
persistence of unimportant parts, such as colour, tex- 
ture of. plumage and hair, form of horns or crests, 
through a series of species differing considerably 
in more essential characters. It also furnishes us 
with a reason for that ‘more specialized structure ” 
which Professor Owen states to be a characteristic 
of recent compared with extinct forms, and which 
would evidently be the result of the progressive 
modification of any organ applied to a special pur- 
pose in the animal economy. 
Conclusion. 
We believe we. have now shown that there is a 
‘tendency in nature to the continued progression of 
certain classes of varieties further and further from 
the original type—a progression to which there ap- 
pears no reason to assign any definite limits—and 
that the same principle which produces this result 
in a state of nature will also explain why domestic 
varieties have a tendency, when they become wild, ' 
to revert to the original type. This progression, 
