272 



THE OLD MOUTH AND THE NEW. 



-St. 



Fro. 179. 



Fig. 180. 



Figs. 179 and 180. — Diagrams showing the location of the principal viscera, such as the enteric pouches, coxal 

 glands, malpighian tubules, lung books and gills. A, Scorpion; B, spider. 



Fig, i8r. Fig. 182. 



Figs. 181 and 182. — Hypothetical forms leading to the condition in vertebrates. 



