ADAPTATION 53 
waves of sound are apparently transmitted to the 
drum of the ear directly through the bones of the head. 
The external openings of the nostrils are placed quite 
on the upper surface of the head, so that the animal 
can breathe whilst almost completely submerged ; and 
the larynx is so modified that the function of swallowing 
does not interfere with that of breathing. Perhaps the 
most remarkable feature of all is the enormous develop- 
ment of the head, and especially of the mouth. The 
huge jaws, in combination with the extraordinary plates 
of whalebone which fringe the edges of the mouth and 
act as a sieve, enable the animal to get its nutriment 
from the minute free-swimming creatures with which 
the surface waters of the ocean abound. Associated 
with this special method of feeding is the fact that 
teeth are only to be recognised in the embryo, and 
afterwards entirely disappear. 
The whales differ in all these points from any other 
mammals, and failing almost any of these differences, 
would not be able to live in the special conditions in 
which they find themselves. It must therefore be 
admitted that we have here a case of very close adapta- 
tion of an animal to its natural surroundings, and one 
which extends to almost every detail of its structure. 
Darwin himself, moreover, has been at special pains to 
show how some of the most remarkable of these 
structural adaptations may possibly have arisen 
through natural selection. 
One of the most remarkable cases of mutual adapta- 
tion, in which an animal and a plant are associated 
together, is shown by the method of fertilization 
