352 Darwin, and after Darwin. 
be regarded as intentionally preparatory to the 
various uses which they subsequently acquire. 
Now this argument, forcible as it appears at first 
sight, is really at fault both in its premiss and in its 
conclusion. By which I mean that, in the first place 
the premiss is not true, and, in the next place, that 
even if it were, the conclusion would not necessarily 
follow. The premiss is, “that every modification of 
structure must have been functionless at first, when it 
began to appear;” and the conclusion is, that, gud 
functionless, such a modification cannot have been 
caused by natural selection. I will consider these two 
points separately. 
First as to the premiss, it is not true that every 
modification of structure must necessarily be function- 
less when it first begins to appear. There are two 
very good reasons why such should not be the case in 
all instances, even if it should be the case in some. 
For, as a matter of observable fact, a very large 
proportional number of incipient organs are useful 
from the very moment of their inception. Take, for 
example, what is perhaps the most wonderful instance 
of refined mechanism in nature—the eye of a verte- 
brated animal. Comparative anatomy and embryology 
combine to testify that this organ had its origin in 
modifications of the endings of the ordinary nerves 
of the skin. Now it is evident that from the very 
first any modification of a cutaneous nerve whereby it 
was rendered able, in however small a degree, to be 
differently affected by light and by darkness would be 
of benefit to the creature presenting it; for the 
creature would thus be able to seek the one and shun 
the other according to the requirements of its life. 
