404 THE STRUCTURE AND LIFE OF BIRDS chap. 



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. W 7 hen 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 



