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- 
Fic. 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 
