444 



ZOOLOGY 



SECT. 



series of ring-like constrictions ; the segments, which are very 

 numerous, amounting to about 150, are somewhat longer towards 

 the anterior end than they are further back. 



At the extreme anterior end is a rounded lobe, the prostQWflwn, 

 immediately behind and below which is the opening of tnemouth. 

 Next to the prostomium is the most anterior segment, the peri- 

 stomium, which bounds the mouth behind. The eyes and tentacles 

 present in Nereis are not represented. On the most posterior 



B 



Fi(J, 363. Lumbricus. A, entire specimen, lateral view ; B, ventral view of anterior portion 

 of the body, magnified. 1, prostomium ; 15, 33, fifteenth and thirty-third segments. 

 Each of the black dots represents a pair of setse. (After Vogt and Jung.) 



segment, the anal segment, is a small median opening, the anal 

 aperture. A limited region of the body in front of the middle, 

 comprising five or six segments, has a swollen appearance ; this is 

 termed the clitellum. There are no parapodia like those of Nereis, 

 but running along the lower surface of the worm are to be recognised 

 with the aid of a lens four double rows of short bristles or setse 

 (Fig. 364), a pair of each row occurring in each segment, which thus 

 possesses eight altogether. The extremities of all these setae are 

 directed backwards, and they act as fulcra for the forward move- 



