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 prostomium, 

 immediately behind and below which is the opening of the mouth. 

 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 



FIQ. 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 setae. (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 setae 

 (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- 



