CHAPTER XV 



CLASSIFICATION 



STRICTLY speaking, classification is not part of the 

 subject of this book. But since it is based on 

 structure, it cannot be entirely passed over. And, in 

 fact, it cannot be properly studied without a great 

 deal being learnt beyond the distinguishing marks of 

 species, genera, and families. 



The aim of the classifier is to discover the relation- 

 ship of bird to bird and arrange them in natural 

 groups. If the system be one that enables the learner 

 easily to identify a specimen, so much the better, but 

 that is not the object in view. The term relationship 

 has gained a far more definite meaning, since the theory 

 of evolution has been generally adopted. If two 

 animals are described as related to one another, the 

 meaning is that they are descended from the same 

 ancestors. If taken in the broadest sense, this is a 

 mere truism, since it is held that all species have been 

 developed from one. It must be understood to mean 

 that, if the two lines of descent be followed upward, 



