THE DIGESTIVE SYSTEM 13 
end of the heart toward the head opens into the body cavity. 
When the heart contracts, the blood it contains is forced forward, 
and when it expands, more blood is admitted through the side valves. 
The Digestive System 
There is a fairly close parallel between the digestive system of in- 
sects and that of some higher animals. The various organs concerned 
Fig. 12.— Digestive system of an insect. (Diagrammatic.) Original. 
are much modified in many species, according to their food habits; 
but taking a typical group, we find the following parts : 
From the mouth the food passes through a pharynx and is con- 
veyed by a gullet or csophagus to a crop, which serves as a storage 
place. Thence it enters the gizzard, where it is ground up, and so 
passes on into the stomach, where part of the digestion and absorp- 
