94 INSECTS. 



The seizure of food is effected by some or all of these 

 parts, assisted in a few cases by armed fore legs. Masti- 

 cation, when necessary, is effected by the mandibles and 

 lacinise of the maxillae 



Two types of insect mouths may be noted, adapted 

 respectively (1) for sucking and (2) for biting. Sucto- 

 rial mouths are widely different in structure, some being 

 armed for making punctures, others wholly unarmed. In 

 some insects with suctorial mouths, the pharynx (some- 

 times other parts of the alimentary canal) is provided 

 with muscles, and capable of distention, and, thus modified, 

 it becomes a pumping organ. 



Digestion is effected jby the crop (when present), gizzard, 

 and stomach, aided by secretions from the salivary glands 

 and gastric caeca. 



Circulation is effected at first by the passage of the 

 digested food through the walls of the alimentary canal, 

 out into the blood. The blood bathes all the internal 

 organs, taking to each the material needed for cell con- 

 struction. It courses posteriorly through the body cavity, 

 enters the dorsal vessel by lateral valves, is propelled 

 forward, and passes out toward the head through the 

 single rudimentary artery. 



Respiration is effected either by spiracles or by tracheal 

 gills. The former are adapted for aerial, the latter for 

 aquatic, respiration. Spiracles are situated on the sides 

 of the body, and open into tracheae, which unite into 

 longitudinal lateral trunks, and send their numerous 

 branches to every vascular part of the body. Some 

 aquatic insects have aerial respiration ; i.e., they obtain 

 their air supply from above the surface of the water. 

 In these the spiracles usually open beneath the wings, 

 where air is stored that has been obtained at the surface 

 and carried down below. 



Tracheal gills are adapted for breathing the air that 



