LIFE PROCESSES IN ANIMALS 277 



ing the body fluids. This preparation for diffusion is 

 known as digestion. In this process the food is first 

 broken up into small bits and parts of it are dissolved. 



Digestive 

 Canal 



Fig. 133. Diagram of a longitudinal section of a hydra showing 

 a simple digestive system with only one opening, the mouth. Food 

 is digested by the cells lining this digestive cavity. 



Then some chemical action takes place. This is brought 

 about by juices which are secreted by cells lining, or 

 opening into, the alimentary canal. Frequently masses 

 of these cells form organs, called glands, whose duty it is 



