146 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
furnished by the general proof of evolution elsewhere, but there is 
likewise the more special correspondence between the whole of our 
anatomy and that of our nearest zodlogical allies. Now the force of 
this latter consideration is so enormous that no one who has not 
studied human anatomy can be in a position to appreciate it. For 
without special study it is impossible to form any adequate idea of the 
intricacy of structure which is presented by the human form. Yet it 
is found that this enormously intricate organisation is repeated in all 
its 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 the process of becoming obsolete, 
and therefore occur as mere vestigial records of a former state of 
things. For example, throughout the vertebrated 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. 19). 
Now the organisation 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 as examples, 
by not only restricting these to cases which occur in our own organisa- 
tion; but of them I shall mention only such as refer us to the very 
Jast stage of our ancestral history—viz., structures which have become 
obsolescent since the time when our distinctively human branch of 
the family tree diverged from that of our immediate forefathers, the 
Quadrumana. 
