404. THE STRUCTURE AND LIFE OF BIRDS cHapP. 
this system the field of our knowledge would be very 
limited. By our own observation we lay hold of 
isolated pieces of information, which, unaided, we 
should never be able to put in their proper setting. 
When we see a Golden Plover in autumn we want to 
know whence and whither he is travelling. When 
we find that the Gray Crow visits the realms of the 
Black Crow, but does not stay to nest there, we want 
a map to show us how these two, so alike that they 
may, perhaps, be considered to form one species, 
have divided the greater part of the Old World 
between them. When we see how our Cuckoos have 
perfected the parasitic habit, we, naturally, wish to 
know of other birds which are advancing towards or 
have attained the same unamiable perfection. Not 
only does the reading of books on natural history 
enable us to connect isolated observations and vastly 
extend the range of our knowledge; it enables us 
also to observe more. Our power of seeing grows 
with our knowledge, if we only keep it alive and do 
not deaden it through want of exercise. When you 
travel in a country for the first-time, if you have 
some previous knowledge of it gained from other 
travellers or from books, you will see far more than 
if you come to it quite raw. 
If the study of birds is to have a solid foundation 
it must include some study of their anatomy. This, 
though we speak of it metaphorically as the founda- 
tion, need not necessarily come at the beginning. 
The point to be insisted on is, that to leave it out is 
to leave out what is indispensable. Flight is, in any 
case, a very difficult subject ; it is more difficult if 
