The Framework of the Bird 97 
the front view of a section would be something like 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 cn two points in 
these side fins, and gradually 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. 
