10 THE STORY OF BIRD-LIFE. 



laboriously fitted and pieced together, not once 

 but many times. We have to work in this, much 

 as detectives work, and many of our '' clues " are 

 about as useful ! 



From the evidence which we have collected 

 so far, we gather that what we now know as a 

 bird has reached its present form by a slow 

 process of change from some other, which was 

 probably, more or less, like what we designate 

 to-day a reptile, e.g. lizard. We say more or 

 less, advisedly ; for the lizard, in its turn, has an 

 equally mysterious origin. One reason then for 

 thinking the bird in some way reptilian is because 

 it shares many things in common with this group, 

 things which occur nowhere else outside, things 

 that are shared by both, probably by virtue of 

 descent from a common stock. 



The bird has risen in the world so as to rank, 

 by common consent of men of science — who fill 

 the part of Nature's Herald's Office — higher than 

 the reptiles. These represent, to-day, its poor 

 relations. 



This gradual change of form, from a more or 

 less like and uniform beginning, the ancestral 

 stock, and the division of this stock into two 

 great classes reptiles and birds, we call evolution. 

 Exactly how this evolution has come about even 

 those best qualified to speak do not entirely 

 agree. 



The hypothesis most generally in favour at 

 the present day is that of Darwin and Wallace, 

 and known as "Natural Selection." According 

 to this hypothesis the interaction of living organ- 

 isms, one upon another, involves a " struggle for 



