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, 



