INTRODUCTORY 7 



in the embryo of, say, a duck, we shall find that it is really made up 

 of six or seven separate vertebrae, which have become, as it were, 

 telescoped. Now, each of these represents one of the feather-bearing 

 vertebrae in the tail of the Archseopteryx ; but by this process of " tele- 

 scoping," this shrinking in length, they have brought the bases of 

 the feathers they supported close together in the fan-wise fashion 

 we have just described. Here, then, we have a lesson in the evolution 

 of birds — a transformation which will go far to help tov/ards realising 

 how similar changes could bring about the evolution of the reptile 

 into the bird. Some day, without doubt, some yet older form of 

 bird will be discovered, and this will show yet more reptilian characters. 



Birds, then, in the possession of feathers, are unique in the scheme 

 of nature ; so that by this character alone we may distinguish them 

 from all the remaining backboned animals, while there can be no 

 sort of doubt but that they owe their descent from some reptilian 

 ancestor. Let us now pass on to consider one or two other pecu- 

 liarities of birds — peculiarities which have gone on developing and 

 perfecting since the time of splitting off from the reptile stock. 



Surely the most important of these is to be found in the fore- 

 limb. This we know as the " wing." Even stripped of its feathers, 

 we could trace the wing of the bird from the fore-leg of any other 

 animal. Yet it cannot be used as an absolutely distinctive character, 

 since in some of the Ostrich tribe, for example, it has become de- 

 generate, and so reduced in size as to be hardly recognised ; while, 

 if we take fossil forms into consideration, we shall find that it be- 

 comes still more dwarfed, until, as in the Moas, it is lost altogether. 



The principal features in which it differs from the fore-limb of 

 other animals are to be found in the bones of the wrist and hand. 

 In the wrist only two separate bones can be found, though in the 

 embryo the rudiments of several can be made out ; these disappear, 

 however, before hatching takes place. The bones of the hand and 

 fingers are reduced to three in number — the thumb and first and 

 second fingers. The first portion of these finger-bones — which 

 answer to the bones that, extending between the wrist and the bases 

 of the fingers, make up the palms of our hands — are firmly welded 

 together, the base of the thumb being hardly traceable. The second 

 and third are welded together at each end, enclosing a space, while 



