CHAP. I. THEIR SENSES. 29 



devoured. Nevertheless, worms do not in- 

 variably leave their burrows when the ground 

 is mcide to tremble, as I know by having 

 beaten it .with a spade, but perhaps it was 

 beaten too violently. 



The whole body of a worm is sensitive to 

 contact. A slight puff of air from the mouth 

 causes an instant retreat. The glass plates 

 placed over the pots did not fit closely, and 

 blowing through the very narrow chinks thus 

 left, often sufficed to cause a rapid retreat. 

 They sometimes perceived the eddies in the 

 air caused by quickly removing the glass 

 plates. When a worm first comes out of its 

 burrow, it generally moves the much ex- 

 tended anterior extremity of its body from 

 side to side in all directions, apparently as an 

 organ of touch ; and there is some reason to 

 believe, as we shall see in the next chapter, 

 that they are thus enabled to gain a general 

 notion of the form of an object. Of all their 

 senses that of touch, including in this term 

 the perception of a vibration, seems much the 

 most highly developed. 



In worms the sense of smell apparently is 

 confined to 'the. perception, of certain odours, 



