THE LAMARCKIAN THEORY 241 



organ, develops it and causes it to acquire a size and 

 strength it does not possess in animals which exercise 

 it less. A bird driven through want to the water to, 

 find the prey on which it feeds, will separate its toes 

 whenever it strikes the water or wishes to displace it- 

 self on its surface. The skin uniting the bases of the 

 toes acquires, through the repeated separating of the 

 toes, the habit of stretching; and in this way the broad 

 membrane between the toes of ducks and geese has 

 acquired the appearance we observe to-day. Similar 

 efforts to swim, that is to repell the water and move 

 in it, have stretched the membranes between the toes 

 of frogs, sea-turtles, otters, beavers, etc. . . . 

 Likewise, . . . the shore birds which do not care 

 to swim, but must approach the water in order to ob- 

 tain food, are continually in danger of sinking into 

 the mud; but wishing to act so that their body shall 

 not fall into the liquid, they try their best to extend 

 and lengthen their feet. Owing to the habit those 

 birds acquire, of extending and lengthening their feet, 

 they find themselves raised as upon stilts, having grad- 

 ually grown long legs, bare of feathers up to their 

 thighs or even higher." G 



Lamarck mentions other examples such as the 

 tongue of the ant-eater, the eyes of fishes which are 

 bilateral in the majority of species and asymmetrical in 

 those that swim on one side and receive a greater 



« Vol. I, p. 248. 



