CH. I] 



EARTHWORMS AND LEECHES 



is very necessary in the rapid retrograde movement of a 

 worm darting back into its burrow. If a worm is placed 

 on a highly polished horizontal surface the contractions 

 of its body do not result in any definite movement but 

 merely in writhings. On the other hand, worms can climb 

 along over nearly vertical surfaces provided these are 

 rough. I have seen them moving at a good speed up 

 a " dry wall " built of Bargate stone a coarse-grained 

 sandstone whose surface is admirably adapted to afford 



Fig. 2. A genital seta (grooved) from 26th segment of L. terrestris; 

 actual length 1'75 mm. ; and, below, an ordinary seta of the same 

 individual ; actual length 1-42 mm. The faintly indicated tube 

 round the right-hand (inner) portion of the figures represents the 

 seta sac. 



hold for the numerous seta3. If a living worm be held 

 in the hand the manner of using the setae in ordinary 

 locomotion is easily seen : as the body is elongated the 

 setae are retracted and disappear from sight, but directly 

 the contraction of the longitudinal muscles of the body- 

 wall begins the seise shoot forth from their pits and can 

 be seen plainly by the unaided eye and their points felt 

 by the skin of the hand. . 



Digestion. In addition to the food obtained from the 

 soil worms devour leaves, both fresh and decaying, and 



