The Framework of the Bird 97 



the front view of a section would be something Hke this, 

 the dorsal fin being above and the lateral 

 fins on each side. Now owing to certain laws 

 of mechanics, whenever such a creature as this 

 moved about in the water, the stress of bal- 

 ancing would be thrown most heavily on two points in 

 these side fins, and gradual!}- at these two nodes the fin 

 became more strongly developed; while between these 

 points it degenerated and finally disappeared. So in 

 modern fishes we find the quartet of limbs alone left of 

 this continuous fin or fold of skin. 



Look at a little embryo in the egg, taking one which 

 has been incubated for six or seven days, and see the 

 curious paddle or fin-like wings and feet — simply four 

 rounded flaps projecting from the body — as unlike the 

 limbs of the chick when it emerges from the egg as can 

 be imagined (see Fig. 367). The ridge or fin of skin in 

 the early, soft-backboned creatures could have been of 

 no use whatever, except in balancing. In fact if we 

 watch a trout carefully, we will see that it is the tail-fin 

 which does almost all the propelling, the front- and hind- 

 limb fins simply acting as guides and balances. 



So in this instance (as indeed in almost every organ 

 in ourselves as well as in birds) we learn that the original 

 function was entirely unlike that which the part now 

 serves. The idea of miraculous change, which is sup- 

 posed to be an exclusive prerogative of fairy-tales, is a 

 common phenomenon of evolution, and the shadows of 

 these miracles of the past are forever coming and going, 

 over the growth of the tiny bird hidden in the egg. 



