EARTHWORMS AND LEECHES 



[CH. I 



is provided with a sure anchor on which 

 it can pull and at the slightest alarm 

 shoot back like stretched elastic into the 

 security of its burrow. At other times 

 the flat tail is employed trowel-wise in 

 smoothing the excrement against the 

 walls of the burrow or in disposing the 

 castings on this side and on that of the 

 mouth of the burrow. 



Locomotion is primarily effected by 

 the alternate rhythmic contractions of the 

 longitudinal and of the circular muscles of 

 the body- wall which contract and elongate 

 successive regions of the cylindrical body. 

 The eight bristles (setae or chaetae) with 

 which each segment is furnished are how- 

 ever of scarcely less importance, inasmuch 

 as they serve as so many little cogs to catch 

 in irregularities of the surface and thus 

 bring about movement in a definite direc- 

 tion. Muscles are attached to the inner 

 parts of the setae and can cause them to 

 shift their positions ; an arrangement that 



Fig. 1. Latero-ventral view of Lumbricus terrestris, 

 slightly smaller than life-size. From Hatschek 

 and Cori. 



1. Prostomium. 2. Mouth. 3. Anus. 4. Open- 

 ing of oviduct. 5. Opening of vas deferens. 

 6. Genital chaetae. 7. Lateral and ventral 

 pairs of chastse. 



xv, xxxn and xxxvn are the 15th, 32nd and 37th 

 segments. The 32nd to the 37th form the 

 clitellum. 



XXXII 



XXXVII 



Fig. 1. 



