150 DIGESTION IN THE LOWER ANIMALS 



broken up by the lip. From this pharynx, the food is 

 forced backward by true peristaltic movements of layers 

 of muscles in the walls of the alimentary canal until it 

 reaches the anal opening. In traversing this canal it 

 passes through several modified regions where it is acted 



Pig. 52 — Cross section of earthworm, showing central intestine (/) and the dorsal 

 fold or typhlosole (T) ; D, dorsal blood vessel ; K, ventral blood vessel ; B. C, 

 body cavity. 



upon by special apparatus or secretions, and in this way 

 the digestible material dissolved out and absorbed through 

 the walls of the canal into the body cavity of the animal, 

 where a fluid similar to the blood in our bodies receives 

 it and distributes it to all parts of the body. In the 

 earthworm the regional division of this tract is of par- 



