INSECTA, A CLASS OF ARTHROPODS 203 



Mouth-parts (biting). 



Upper lip, Labrum, for holding food. 



True jaws, Mandibles, for chewing. 



Accessory jaws, Maxillae, to aid jaws (palpi). 



Lower lip, Labium, to hold food (palpi). 



Thorax. 



Anterior thorax, Prothorax, Movable; legs attached. 



Middle thorax, Mesothorax, Strong; wings and legs. 



Posterior thorax, Metathorax, United to mesothorax wings and 



jumping legs. 

 Legs, 



Functions: walking, clinging, leaping. 



Structure. 



Adaptations: 



Strength of muscles. 

 Length of leverage. 

 Free backward movement. 

 Spines, pads, etc. 

 Point of attachment. 



Wings. 



First pair, planes and protection, concave, stiff, straight. 

 Second pair, thin, folded fan- wise, propellers. 



Abdomen (structure). 



Adaptations for respiration, spiracles, motion of segments. 

 Adaptations for reproduction, ovipositors. 

 Adaptations for hearing, ears. 



Activity requires energy. 



Energy requires food to supply it. 



Food requires oxygen to release its energy. 



Oxygen" supply requires good breathing organs. 

 All this energy requires high nerve control. 



Internal Structure. 



Muscles, complex, strong, and very numerous. 

 Digestion, glands, crop, stomach, caeca, intestine, rectum. 

 Excretion, malpighian tubes. 



Circulation, open system, dorsal, light color blood. 

 Respiration, spiracles, trachea, motion of abdomen. 

 Nervous system, high, senses well developed. 



Development of nervous system : 



Protozoa, direct to protoplasm, sense heat, light, contact. 



Hydra, special nerve cells in groups (ganglia), motor control. 



Worms, ganglia connected, beginning of brain. 



Crustacea, fewer ganglia, cephalization, sense organs. 



Insecta, very high brain ganglia, iew others, great motor control, instinct. 



