198 



THE EVOLUTION OF MAN. 



Worms, we find an independent nerve-system, distinct and 

 separate from the outer skin-covering. This is the " upper 



Fig. 209. — Gastrula of Gastrophysema (Gastrsead-class) . 



Fig. 210. — Transverse section through an embryonic Earth-worm : hs, 

 skin-sensory layer; hm, skin-fibrous layer; df, intestinal-fibrous layer; dd, 

 intestinal-glandular layer ; a, intestinal cavity ; c, body-cavity, or Cceloma ; 

 n, nerve-ganglia ; u, primitive kidneys. 



Fig. 211. — A Gliding Worm (Rhabdoccelum) . From the brain or upper 

 throat ganglion (g) nerves (n) radiate towards the skin (/), the eyes (au), 

 the organ of smell {na), and the mouth (m) : h, testes ; e, ovaries. 



