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 Gastrophysema (Gastraead-class). 



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

 skin-sensory layer; ^m, skin-fibrons layer; (?/, intestinal-fibrous layer; dd, 

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

 ^^, nerve-ganglia; u, primitive kidneys. 



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

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

 the organ of smell {no), and the mouth (in) : h, testes; e, ovaries. 



