350 THE EVOLUTION OF MAN. 



vertebrse, to which the ribs are attached, five lumbar- 

 vertebrae, five cross-vertebrae (inserted into the pelvis), and 

 four or five tail- vertebrae. Each of these represents a 

 corresponding section of the nervous, muscular, and vascular 

 systems, etc. 



A further consequence of the mode of development of 

 the metamera is, that nearly the whole front half of 

 the lyre-shaped germ-shield (Figs. 103, 107) mustre present 

 the future head. The seven primitive vertebrae which 

 occupy the third quarter of the whole length, form the Jieck, 

 so that all the rest of the body originates from only the 

 fourth and last quarter. This proportion seems strange at 

 first, but its phylogenetic explanation, as the result of the 

 terminal budding, is simple. The head portion of the 

 vertebrate animal must accordingly be regarded phyloge- 

 netically and originally as the oldest portion of the body — 

 as a group of a few (six to ten) closely coalescent metamera, 

 which, by continued budding at the posterior extremity, 

 have produced the remainder of the body. The tail, on 

 the other hand, is the most recent part, the latest in order 

 of development. 



As has been already observed, the articulation affects 

 the entire body of the Vertebrate, although the skin shows 

 no external signs of articulation. The primitive vertebral 

 pieces are, therefore, not merely rudiments of future 

 vertebrae ; they are real metamera, or trunk-segments. 

 Each metameron first appears as a nearly cube-shaped, 

 solid, roundly-hexagonal body, entirely composed of cells. 



Fig. 110. — Human skeleton, from the front. 



Fig. 111. — Human skeleton, from the right side. The arms have been 

 removed. (Both figures after H. Meyer.) 



