74 Darwin, and after Darwin. 
details in the bodies of the higher apes. There is no 
bone, muscle, nerve, or vessel of any importance in the 
one which is not answered to by the other. Hence 
there are hundreds of thousands of instances of the 
most detailed correspondence, without there being 
any instances to the contrary, if we pay due regard 
to vestigial characters. The entire corporeal structure 
of man is an exact anatomical copy of that which we 
find in the ape. 
My object, then, here is to limit attention to those 
features of our corporeal structure which, having 
become useless on account of our change in attitude 
and habits, are in process of becoming obsolete, and 
therefore occur as mere vestigial records of a former 
state of things. For example, throughout the verte- 
brated series, from fish to mammals, there occurs in 
the inner corner of the eye a semi-transparent eye-lid, 
which is called the nictitating membrane. The object 
of this structure is to sweep rapidly, every now and 
then, over the external surface of the eye, apparently 
in order to keep the surface clean. But although the 
membrane occurs in all classes of the sub-kingdom, 
it is more prevalent in some than in others—e.g. 
in birds than in mammals. Even, however, where it 
does not occur of a size and mobility to be of any use, 
it is usually represented, in animals above fishes, by a 
functionless rudiment, as here depicted in the case of 
man. (Fig. 10.) 
Now the organization of man presents so many 
vestigial structures thus referring to various stages of 
his long ancestral history, that it would be tedious so 
much as to enumerate them. Therefore I will yet 
further limit the list of vestigial structures to be given 
