256 



THE EVOLUTION OF MAN. 



FIG. 54. 



FIG. 55. 



FIG. 56. 



FIG. 52. The ideal Primitive Vertebrate type, seen from the left side : 

 rnr, medullary tube ; x, chorda ; na, nose ; cm, eyes ; g, ear- vesicle ; md, 

 mouth ; k, gill-body ; ks, gill-openings ; kg, gill-arches ; ma, stomach ; I, 

 liver; d, small intestine; a/, anns; v, intestinal vein; hz, heart; a, body- 

 artery; n, primitive kidney canal; e, ovary; h, testicles; c, body-cavity 

 (visceral cavity) ; 7ns, muscles ; lh, leather-skin (coriuni) ; oh, outer-skin 

 (epidermis) ; /, skin-fold, acting as fin. 



FIG. 53. Same as above, viewed from the ventral side. 



