272 



THE OLD MOUTH AND THE NEW. 



oil. 



Fro. 179. 



FIG. 180. 



FIGS 179 AND 180 Diagrams showing the location of the principal viscera, such as the enteric pouches, coxa! 



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



lil-i 



FIG. 181. FIG. 182. 



FIGS. 181 AND 182. Hypothetical forms leading to the condition in vertebrates. 



