400 



THE EVOLUTION OF MAX. 



romainder of the body-cavity (cceloina). Of tliese latter — 

 the true coelom-cells — those which invest the intestinal 

 tube and the mesentery (" endocoilar ") originate from the 



c~ 



Fig. 316. — Transverse section through the pelvic resfion and the hind 

 limbs of an embryo Chick in the fourth day of incubation, enlarged about 

 40 times : h, horn-plate ; u', medullary tube ; n, canal of the medullary 

 tube; u, primitive kidneys; x, notochord; e, hind limbs ; h, allantois canal 

 in ventral wall ; t, aorta ; v, cardinal veins ; a, intestine ; d, intestinal- 

 glandular layer; /, intestinal-fibrous layer; ^, germ-epithelium ; r, dorsal 

 muscles ; c, body-cavity, or Ccelom. (After Waldeyer.) 



intestinal-fibrous layer (in Fig. 5, Plate IV., coloured red) ; 

 those which line the inner surface of the external wall of 

 the abdomen (" exocodar ") are, on the contrary, the product 

 of the skin-fibrous layer (coloured blue in Fig. 5, Plate IV.) ; 

 but the sexual cells which make their appearance at the 

 boundary line between the two forms of coelom-cells, and 



