198 



THE EVOLUTION OF MAX. 



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). 



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

 skin-sensory layer; ^in, skin-fibroas layer; <?/, intestinal-fibrous layer; dd, 

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

 w, nerve-ganglia; u, primitive kidneys. 



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

 throat ganglion (;/) nerves (n) radiate towards the skin (/), the eyes (aw), 

 the organ of smell [no), and the mouth (m) : 7i, testes; e, ovaries. 



