64 



The vSecretion of tlie digestive glaud is capable, 

 therefore, of acting upon proteids, starch and fats, or, in 

 other words, it contains proteolytic, amylolytic and 

 lipolytic ferments, like the pancreatic juice of vertebrates. 

 The action of these ferments is to convert colloid materials 

 like starch and proteid into the diffusible materials, sugar 

 and peptone, which are eventually absorbed ; and the 

 intestine must be considered as the place where this 

 absorption is going on, the descending limb from the 

 stomach being probably the main portion concerned. 



The intestine may be divided into three sections, 

 Avhich are of practically the same length : (1) the 

 descending portion (fig. 06, ^4/. c. 3); (2) the ascending 

 portion [Al. e. 4); and (3) the rectum (Al. c. 5). 



(1) The descending limb of the intestine arises from 

 the stomach, not posteriorly, but veutrally, at almost the 

 middle of its length, and passes anteriorly and downwards 

 from the stomach through the digestive gland to the 

 reproductive region of the visceral mass (fig. 1). At 

 the level of the foot this portion of the intestine lies 

 amidst the tubules of the gonad, in the median line, very 

 near to the surface of the visceral mass lying against the 

 adductor miiscle. From this point it curves - forwards 

 towards the free margin of the visceral mass, and in 

 P. niaxintus extends down to the extreme end of the latter, 

 where it bends suddenly and returns as the (2) ascending 

 limb. This lies close to the adductor surface all the 

 way and at first in the median line, but when the point is 

 reached where the descending portion comes near to the 

 adductor, the ascending portion is displaced and lies to 

 the right of it, so that it eventually plunges into the 

 digestive gland on the right side, and lies near the surface 

 on the right side close to the adductor muscle. It passes 

 up to the dorsal surface of the gland, where it lies in the 



