310 THE ACTION OF NATURAL 
the selected portion of each succeeding generation will 
therefore be stronger, swifter, and more thickly furred 
than the last; and if this process goes on for thousands 
of generations, our animal will have again become 
thoroughly in harmony with the new conditions in 
which it is placed. But it will now be a different = 
creature. It will be not only swifter and stronger, 
and more furry, it will also probably have changed in 
colour, in form, perhaps have acquired a longer tail, 
or differently shaped ears; for it is an ascertained 
fact, that when one part of an animal is modified, 
some other parts almost always change, as it were in 
sympathy with it. Mr. Darwin calls this “‘ correlation 
of growth,” and gives as instances, that hairless dogs 
have imperfect teeth ; white cats, when blue-eyed, are 
deaf; small feet accompany short beaks in pigeons; 
and other equally interesting cases. 
Grant, therefore, the premises: 1st. That peculiari- 
ties of every kind are more or less hereditary. 2nd. 
That the offspring of every animal vary more or less 
in all parts of their organization. 3rd. That the 
universe in which these animals live, is not absolutely 
invariable ;—none of which propositions can be denied ; 
and then consider, that the animals in any country 
(those at least which are not dying out) must at each 
successive period be brought into harmony with the 
surrounding conditions; and we have all the elements 
for a change of form and structure in the animals, 
keeping exact pace with changes of whatever nature 
in the surrounding universe. Such changes must be 
