54 



Darwin, and after Darwin. 



Now I have chosen the case of the whale and 

 porpoise group, because they offer so extreme an 

 example of profound modification of structure in 

 adaptation to changed conditions of life. But the 

 same thing may be seen in hundreds and hundreds 

 of other cases. For instance, to confine our attention 



FIG. 4. Paddle of Whale compared with Hand \.( Man. Drawn 

 from nature (X. Coll. Surf. Mus.). 



to the arm, not only is the limb modified in the whale 

 for swimming, but in another mammal the bat ^it 

 is modified for flying, by having the fingers enor- 

 mously elongated and overspread with a membranous 

 web. 



In birds, again, the arm is modified for flight in 

 a wholly different way the fingers here being very 



