120 



Itivertebrata. 



to the eyes and appendages, while the thoracic ganglia 

 supply the limbs. Some cave-dwelling insects have 

 no eyes, others have these organs rudimental. The 

 digestive canal of insects consists of a stomach to 

 FIG. es. which the long oesophagus or 



gullet leads from the mouth ; 

 to this a thin walled sac or 

 sucking stomach may be ap- 

 pended as in butterflies, in 

 others there is a gizzard with 

 hard horny tooth-like pro- 

 cesses, and this is followed 

 by the glandular thin- walled 

 true digestive stomach which 

 ends in an intestine, whose 

 length depends on the nature 

 of the food, being longer in 



Nervous system of Beetle, f 



showing central double nerve thOSC that feed On SOlld than 

 cord and chain of ganglia. 



matter, and longer in the herbivorous than in the 

 predaceous forms. Glandular tubes opening into 

 the end of the intestine exist in many insects, and 

 from their first describer are known as Malpighian. 



Some insects are luminous. In the glow-worm 

 (Lampyris noctilucd] there is a large fatty body in 

 FIG. 69. the abdomen richly supplied with 



tracheae and nerves from which a 

 bright light is emitted. The fire-fly 

 (Elater noctilucus) sends out light 

 from two oval spots on the thorax. 

 Grasshoppers and crickets emit 

 sounds by rubbing one part of the 



