PREFACE 
THE aim of this book is an ambitious one. It 
attempts to give good evidence of the development 
of birds from reptilian ancestors, to show what 
modifications in their anatomy have accompanied 
their advance to a more vigorous life, and, after ex- 
plaining, as far as possible, their physiology, to make 
clear the main principles of their noble accomplish- 
ment, flight, the visible proof and expression of their 
high vitality. After this it deals, principally, with 
the subjects of colour and song, instinct and reason, 
migration, and the principles of classification, and, 
lastly, gives some hints as to the best methods of 
studying birds, The field is a wide one, but this is 
not in every way a drawback. Specialisation has its 
evils as well as its advantages. Many of our best 
ornithologists write admirably of the life and habits 
of birds, but leave out of sight their anatomy and 
physiology. Thus they separate things which in 
nature are mutually dependent. The anatomists 
and physiologists, on their side, limit themselves 
sternly to their own departments. Their works, 
