GENERAL ANATOMY OF THE LEECH. 163 



a. The digestive tract consists of a buccal pouch, a 

 pharynx, a stomach, and an intestine. The buccal pouch 

 may be examined later. In the other parts, notice : 



1. The muscular, thick-walled, tubular pharynx, which 

 forms about the first tenth of the total length of the di- 

 gestive tract. It is bound, by radiating muscular fibres, 

 to the body wall. 



It is much larger in the middle than at the ends, where 

 the wall contains circular muscles, which may by their 

 contraction entirely close the tube. 



3. The " stomach " is a large sacculated pouch, which 

 joins the pharynx abruptly, and nearly fills the body cav- 

 ity. Its walls are much thinner than those of the pha- 

 rynx, and are only very slightly muscular. It occupies 

 about five-sixths of the total length of the body, and is 

 divided, by deep constrictions which run nearly to the 

 middle line, into eleven pouches or chambers, each of 

 which, except the last, fills the body cavity of one somite, 

 while the constrictions which separate the pouches cor- 

 respond to the partitions between the somites. These 

 partitions may be seen to run into the spaces between the 

 pouches, so as to form imperfect dissepiments between the 

 cavities of adjacent somites. 



The cavity of the stomach is made up : 



(i.) Of a central tube, which is continuous with the 

 pharynx along the middle of the body, and is greatly con- 

 stricted at each dissepiment. 



(ii.) Of the cavities of the sacculi upon each side of 

 this central tube. 



The squeezing to which the blood is subjected in this 

 " stomach," in order to separate the fluid from the solid 

 portions, is effected by the pressure of the outer wall of 

 the body, only slightly aided by the muscles of the stom- 

 ach itself. 



