birds' flight, and birds' wings. 57 



humiliation to us. For many generations man 

 has been sighing, with David, for the wings of 

 the dove — or some other bird — that he too 

 might rise as they rise, and soar as they soar, - 

 at will from one new sphere to anotheV; that 

 he might at will change the fog-laden atmos- 

 phere of a crowded city for the bright blue 

 skies and sunshine of the open country. But 

 he has sighed in vain. Many have been the 

 attempts and as many the failures to accomplish 

 this and success seems almost as far otf as 

 ever. 



The power of flight, as a moment's reflection 

 will remind us, is by no means confined to the 

 birds. The butterflies and moths, flies and 

 beetles, and the bats, in our own class — the 

 mammalia — are all superb fliers. All fly by means 

 of wings, but — and this has probably never be- 

 fore occurred to many of my readers — these 

 wings are not in all cases of precisely the same 

 nature and origin. The wing of the butterfly or 

 of the bee, when compared with that of the bird 

 or the bat, is said to be an "analogous structure"; 

 but the wings of the bird and bat homologous 

 structures. To put it more plainly, when we 

 say that the wing of the butterfly is analogous 

 to, or is the analogue of, the wing of the 

 bird, we mean that the two organs perform 

 the same function — of sustaining the body in 

 the air, but that they are of difl'erent origin; 

 whilst the wing of the bat and bird are of 

 the same origin, or are homologous. For in- 

 stance, the bat and the bird, like the horse 

 or the dog, or ourselves, have each four limbs, 



