84 ORGANIC EVOLUTION 



that the relations of the embryo to the mother 

 pursue the same intricate course in both cases. 

 Judged by embryolog} 7 , man is a true " placental 

 mammal." Both in the anthropoid ape and in man, 

 we find the nutrition of the embryo effected first by 

 one makeshift — which immediately recalls a plan 

 that was very far from being a makeshift in the 

 case of their common, though distant, ancestors — 

 and then by another, which tells the same tale. 

 Finally, there is established, in each case, that par- 

 ticularly efficient and versatile mode of connection 

 between mother and foetus which is termed the 

 placenta. 1 The comparative study of placentation 

 alone, throughout all the series of mammals from the 

 marsupials (represented by the kangaroo) upwards, 

 would alone suffice to establish the theory of com- 

 mon descent for all such mammals, even were no 

 other lines of d posteriori evidence forthcoming. 

 Here I merely allude to the subject, as it must be 

 referred to in more detail when we come to consider 

 — in another volume — the evolutionary teaching as 

 to the origin of morality. 



Ere we leave the subject of embryology in its 

 relation to human descent I may refer briefly to 

 the history of the human tail. Every now and 

 asrain anatomists hear of the occurrence of a tail in 

 an adult human being ; but such external tails are 

 only very rarely found to contain vertebrae and are 

 usually no more than loose " tags " of fat-enclosing 

 skin. 



1 This wonderful organ is known to human mothers and nurses 

 as the " after-birth," and, when its indispensable work is done, 

 is usually contemptuously thrown " on the back of the fire." 



