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 zoological 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- 

 l^ion; but of them I shall mention only such as refer us to the very 

 last 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. 



