Q2 THE EVOLUTION OF MAN. 



organs ; but I shall be compelled to explain the ontogenetio 

 and the phylogenetic origin of the organs simultaneously; 

 for the further we penetrate into the details of organic 

 development, and the more minutely we study the origin 

 of the separate parts, the more clearly do we see how 

 inseparably the evolution of the germ is connected with 

 that of the tribe. The Ontogeny of the organs is intelligible 

 and explicable only through their Phylogeny ; just as the 

 germ-history of the entire body (the "person") is rendered 

 intelligible only by the history of the tribe. Each germ- 

 form is determined by a corresponding ancestral form. This 

 is as true of the parts as of the whole. 



In endeavouring, with the help of this fundamental law 

 of Biogeny, to obtain a general view of the main features in 

 the development of the separate organs of man, we must, in 

 the first place, consider the animal, and then the vegetative 

 organ-systems of the body. The first main group of organs, 

 the animal organ-systems, is formed by the sensory apparatus, 

 together with the motor apparatus. To the former belong 

 the skin-covering, the nervous system, and the organs of the 

 senses. The motor apparatus consists of the passive organs 

 of movement (the skeleton) and the active organs (the 

 muscles). The second main group of organs, the vegetative 

 organ-system, is formed by the nutritive and the repro- 

 ductive apparatus. To the nutritive apparatus belongs 

 especially the intestinal canal with all its appendages, 

 together with the vascular and renal systems. The repro- 

 ductive apparatus includes the various sexual organs (the 

 germ-glands, germ-ducts, organs of copulation, etc.). 



In earlier chapters (IX. and X.) it has been stated that 

 the animal organ-systems (the instruments of sensation and 



