198 



PHYLUM ANNELIDA. 



mineral matter to more useful form ; while, in covering the 

 surface with earth brought up from beneath, the earthworms 

 have been ploughers before the plough. Darwin calculated 



in 



5 

 5 



' 







that there were on an average over 53,000 earthworms in an 

 acre of garden ground, that 10 tons of soil per acre pass 

 annually through their bodies, and that they cover the 



