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. Gastrnla of Gastrophyseina (Gastrsead-class). 



FIG. 210. Transverse section through an embryonic Earth-worm : hf, 

 skin-sensory layer; hm, skin-fibroas layer; <?/, 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 (aw), 

 the organ of smell (?ia), and the month (m) : h, testes; e, ovaries. 



