DIGESTIVE SYSTEM OF THE EARTHWORM 139 



thus increasing the area of the digestive surface. The intestine, 

 finally, is constricted at each dissepiment so that its structure 

 follows the general metamerism of the body. 



The digestive fluid secreted by the wall cells of the 

 intestine corresponds in its essential features with the pan- 

 creatic juice of mammals. Free acids cannot be detected in 

 the gut where the fluids in general show a slightly alkaline 

 reaction. According to Lesser and Taschenberg albumin is 

 broken down under action of this digestive fluid in 3 1/2 hours 

 at 37 C. if the medium is slightly alkaline, and in 28 1/2 hours 

 if it is slightly acid. According to Abderhalden and Heise a 

 peptolytic ferment is also present which accounts for the slow 

 digestion in an acid medium. The same observers also ex- 

 tracted an amylytic ferment which 

 changes starch into sugar (maltose) 

 and found traces of a fat emulsify- 

 ing ferment. 



The digestive ferments are 

 secreted by gland cells distributed 

 among absorbing cells of the gut 

 epithelium (Fig. 56). In prepara- 

 tion they may be distinctly made , f IG - 56 Cells from the en- 



. . , , . i 1.1 doderm of a worm snowing 



OUt if filled With granules which enlarged gland cells with 



' 



have an albuminous nature, but if 



emptied of granules they become so K - C. Schneider.) 



small and compressed that they are difficult to find. 



The absorption cells are columnar, ciliated, epithelial cells, 

 somewhat broader at the ciliated end. Here there is a 

 typical and characteristic closing 1 apparatus. The free sur- 

 face possesses a cuticle-like covering which bears a hedge of 

 frne, stiff rods, through which the cilia pass from their basal 

 bodies in the cell to the lumen of the gut. These cilia are 

 ibsent on the cells of the typhlosole where fat absorption is the 

 :hief role. The function of the minute rods is unknown 

 out they occur very generally on absorption cells. Granules 

 )f absorbed food-stuffs are often visible in these cells, some of 

 ,vhich may be recognized. Thus, if powdered carmine or indigo 



