DEFENCES OF THE EARTHWORM. 71 



As to protective structures, tlie eartliworin is prol)a])ly one of 

 the most defenceless of animals. Nevertheless there are certain 

 structures which are clearly for this purpose. The cuticle wliicli 

 covers the surface is a thin but tough memljraiie wliidi ju-otects 

 the delicate skin from direct contact with hard oljjects. It 

 passes into the mouth and lines the alimentary canal as far down 

 as the beo^inninc: of the stomach-intestine. In the irizzard. 

 where food is ground up, the cuticle is prodigicjusly thick and 

 tough, and must form a very effective protection for tlie soft 

 tissues beneath it. The main defence of the animal lies, how- 

 ever, not in any special armor, but in those instincts which lead 

 it to lie hidden in the earth during the day and to venture forth 

 only in the comparative safety of darkness. 



