I INTRODUCTORY 5 
apparatus— means higher temperature, comparative 
superiority to external conditions, greater vitality, 
and greater enjoyment of life. And the changes from 
first to last have not been additions of new organs, but 
adaptations of existing materials. 
The differences between a bird and a reptile are so 
striking, they lie so much on the surface, that we are 
in danger of seeing the differences only and passing 
over the resemblances, some of which are obscure and 
require a minute knowledge of anatomy. But there is 
no reason why the pedigree should be taken on trust. 
Much of the evidence that enables us to trace it is 
easily intelligible. 
After trying to make clear the development of the bird 
from reptile ancestors, I shall go on to describe (1) his 
structure in more detail and the work done by the 
different organs, (2) what cannot be dissociated from 
his structure, his life and habits. 
