INTRODUCTION xxv 



and examine the different kinds included in each, but 

 boldly, after an introduction on the general structure of 

 birds, the phylogeny of birds is discussed, that is to 

 say, their genetic relationship to the reptiles and the 

 evidences thereof, and a " family tree" showing- the 

 main lines of the descent of birds and the relationships 

 to one another of the numerous groups of birds is given. 

 Then we have a chapter on Geographical Distribution 

 followed by others on the Seasonal Life of Birds, on 

 Migration, on Peculiar Interrelations (such as those 

 of the Cuckoos), on the Relations of the Sexes (including 

 courting, display, fighting, song and music). Then we 

 come to chapters on Nidification, Eggs, Care of Off- 

 spring, Nestling Birds and what they teach (a subject 

 greatly studied by Mr. Pycraft), the Life-history of 

 Birds, Variation, Natural Selection and Artificial Selec- 

 tion in the case of Birds, Sexual Selection, Adaptations 

 and Convergence of form in distinct groups (the latter 

 better called " homoplasy "). These and similar topics 

 are discussed by Mr. Pycraft at greater length than would 

 be possible in a systematic treatise on birds ot the usual 

 scope. ^ The survey of bird-life thus given is a very 

 complete one, and many interesting features of it, liable 

 to be too briefly treated in a book arranged on classi- 

 ficatory lines, are here duly dealt with. The illustrations 

 are of great value, for they are not old but new, and 

 they are admirably executed. 



I may cite here a few of the more interesting views 

 which Mr. Pycraft advances in the present volume. 

 In regard to the subject of migration (see page 89), he 

 has promulgated one or two new ideas. He holds 

 that the trend of migration is, throughout the world, due 

 north and south, as far as physical conditions render 

 this possible. It appears as a consequence of this that 



