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 
Fic. 4.—Paddle of Whale compared with Hand of Man. Drawn 
from nature (XR. Coll. Surg. 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 
& 
