xviii INTRODUCTION 



no more make the tail of a bird than hair makes the 

 tail of a dog. Now if we examine this bony plate in 

 the embryo, say, of a duck, we shall find that it is 

 really made up of six or seven separate vertebrae, 

 which have become, as it were, telescoped. Each of 

 these represents one of the feather-bearing vertebras 

 in the tail of Archsopteryx ; but by the process of 

 telescoping — this process of shrinking — they have 

 brought the bases of the feathers they supported close 

 together in the fan-wise shape we have just described. 



Here, then, we have a lesson in the evolution of 

 birds — a transformation that will go far to help realise 

 how similar changes could bring about the evolution 

 of the ancient reptile into the modern bird. Some 

 day, without doubt, a yet older form of bird mil be 

 discovered, which will show even more reptilian char- 

 acters. 



Another strong proof of the identity of the two 

 forms in origin is found in the study of the develop- 

 ment of the egg into the chick. It is well known that 

 the gradual changes which may be studied here re- 

 peat to some extent the history of the species from the 

 earliest to the latest form, and the fact that the early 

 embryonic development of birds agrees with the be- 

 lief that they are descended from the same ancestral 

 form as the reptiles, is supported by the conclusion 

 arrived at by embryologists. 



Birds, then, in the possession of feathers, are tmique 

 in the scheme of nature; so that by this character 

 alone they are distinguished from all other backboned 

 animals. There can be no doubt that they owe their 

 descent to some reptilian ancestor. Let us now pass 



