440 THE EVOLUTION OF MAN. 



human body includes no single organ which is not in- 

 herited from Apes ; but, by means of our fundamental law 

 of Biogeny, we can trace the origin of our several systems 

 of organs yet further down to various lower ancestral 

 grades. Thus, for instance, we can say that we have 

 inherited the earliest organs of our body, the outer-skin 

 (epidermis) and the intestinal canal, from the Gastraeads, 

 the nervous and muscular systems from the lower Worms 

 (Archelminthes), the vascular system, body -cavity (cceloma), 

 and blood from Soft Worms (Scolecida), the notochord and 

 the gill-intestine from Chorda Animals, the differentiated 

 organs of sense from the Cyclostoma, the limbs and the 

 Mullerian ducts from Primitive Fishes (Selachii), and the ex- 

 ternal reproductive organs from Primitive Mammals (Pro- 

 mammalia). When we stated the " law of the ontogenetic 

 connection of systematically allied forms," and determined 

 the relative age of the organs, we saw how we could draw 

 such phylogenetic conclusions as these from the ontogenetic 

 succession of the organ-systems (vol. i. p. 390 ; ii. 357). 



By the help of this important law and of Comparative 

 Anatomy, we were also enabled to determine definitely 

 "man's place in nature," or, as we may say, to assign to 

 man his position in the system of the animal kingdom. It 

 is now usual, in the more recent zoological systems, to 

 distribute the whole animal kingdom into the seven tribes, 

 or phyla, which are again sub-divided, in round numbers, 

 into about forty classes ; and these classes into about 

 two hundred orders. According to his whole organization, 

 Man is undoubtedly, primarily, a member of but a single 

 tribe, that of Vertebrates ; secondly, he is a member of but 

 a single class, that of Mammals ; and, thirdly, a member 



