Criticisms of Theory of Natural Selection. 355 
that a wing could be of no conceivable use until it had 
already acquired enormous proportional dimensions, 
as well as an immense amount of special elaboration 
as to its general form, size of muscle; amount of blood- 
supply, and so on. For, obviously, not until it had 
attained all these things could it even begin to raise 
the animal in the air. But observe how fallacious is 
this argument. Although it is perfectly true that a 
wing could be of no use as @ wing until sufficiently 
developed to serve the purpose of flight. this is merely 
to say that until it has become a wing it is no use as 
a wing. It does not, however, follow that on this 
account it was of no prior use for any other purpose. 
The first modifications of the fore-limb which ended 
in its becoming an organ of flight may very well have 
been due to adapting it as an organ for increased 
rapidity of locomotion of other kinds—whether on 
land as in the case of its now degencrated form in the 
ostrich, or in water as in the case of the expanded fins 
of fish. Indeed, we may see the actual process of 
transition from the one function to the other in the 
case of “ flying-fish.” Here the progressive expansion 
of the pectoral fins must certainly have been always 
of use for continuously promoting rapidity of loco- 
motion through water; and thus natural selection 
may have continuously increased their development 
until they now begin to serve also as wings for carry- 
ing the animal a short distance through air. Again, 
in the case of the so-called flying squirrels we find the 
limbs united to the body by means of large extensions 
of the skin, so that when jumping from one tree to 
another the animal is able to sustain itself through a 
long distance in the air by merely spreading out its 
Aa 2 
