USE OR DISUSE OF ORGANS. 133 



Upland geese, that do not frequent water, 

 have webbed feet although they never swim. 

 The water - hen lives habitually in water, 

 but has not developed webbed feet like the 

 duck, neither has the water-ousel, although 

 it gets its food by diving. The ostrich 

 frequently uses its wings, but has not 

 developed the faculty of flight, and Darwin 

 explains the failure in these words : "A 

 moment's reflection will show what an 

 enormous supply of food would be necessary 

 to give this huge bird of the desert force 

 to move its huge body through the air " ; 

 that is to say, in this case use did not 

 develop cause failed of its normal effect 

 because of the consequence. But this is an 

 argument in favour of design and against 

 Darwin's theory. 



These examples of use and disuse to bring 

 about modifications of structure conclusively 

 prove that there is no general law that use 

 or disuse of parts develops specific variation. 



Acquired Habits. 



Darwin does not give any examples of 

 animals acquiring habits. 



He assumes that certain habits have been 



