DEFENCES OF THE EARTHWORM. 71 



As to protective structures, the earthworm is probably one of 

 the most defenceless of animals. Nevertheless there are certain 

 structures which are clearly for this purpose. The cuticle which 

 covers the surface is a thin but tough membrane which protects 

 the delicate skin from direct contact with hard objects. It 

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

 as the beginning of the stomach-intestine. In the gizzard, 

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

 tough, and must form a very effective protection for the 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. 



