PR O OFS OF E VOL TJTION. 
25 
across the dry land in this way. Thus the swim- 
bladders of certain of the early fishes gradually 
developed into lungs, the gill-arches into ears; 
the head enlarged; the circulation increased; a 
warmer current filled the veins; the tail-fin, not 
having much to do, dwindled to an ornamental 
appendage,— and then and there a quadruped was 
born. 
Again, when Nature wanted a bird, she didn't 
make one out of raw material, as we are told, 
full-winged to soar away, but “worked over” the 
old fabric, just as thrifty housewives do, and do so 
wondrously well. Therefore, if wings are needed, 
the fore-limbs must go — they must be transformed 
into wings. Ages pass on; the earth is filled 
with birds, beasts, and creeping things, but the 
quadruped is king. He has grown to enormous 
size and strength, and appears in almost endless 
varieties. The struggle for existence has preserved 
the strongest, the most cunning, and those most 
highly skilled in the art of food-getting. The 
fierce warfare through which all living creatures 
have passed, would naturally sharpen all the 
-senses, and stimulate, little by little, the power to 
observe and discriminate as to friend and foe, and 
