WHAT EVOLUTION IS 75 



would respond by extra growth. In 

 this way the skin between the toes 

 would become firmer, tougher, and 

 more extensively developed. These 

 effects would be increased in the de- 

 scendent stock, and as they accu- 

 mulated generation after generation, 

 the passage would be accomplished 

 from the webless foot of the land 

 bird to the webbed foot of the water 

 bird. 



Lamarck conceived that the gi- 

 raffe's neck, to take another of his 

 examples, was lengthened by a similar 

 process. These animals were sup- 

 posed to browse among the branches 

 of trees. In their endeavors to reach 

 the leafy food, they would naturally 

 exert the muscles of the neck and this 

 activity would induce an extra flow of 

 blood to that region. In consequence 

 the muscles, bones, and other parts of 

 the neck would increase in size, just 



