THE CONQUEST OF THE DRY LAND 227 



they found food enough by eating the soil for 

 the sake of the plant remains in it, and by col- 

 lecting plant crumbs on the surface. The 

 more they worked, age after age, the more 

 soil they made, and the more plants there 

 were with crumbs to eat. In their newly dis- 



FIG. 28. DIAGRAM OF SOME BURROWERS. 



An Earthworm to the right, a Mole-cricket to the left, a 



Mole in the middle. 



covered country below the ground the earth- 

 worms lived, if not in ease, at least in safety. 

 Meanwhile, however, evolution was in prog- 

 ress. The second great invasion of the dry 

 land had occurred, which led on to creatures 

 like centipedes and burrowing, carnivorous 



