290 ARTICULATA : INSECTA. 



altogether forming a net- work of veins and veinlets. The five main 

 veins, beginning at the front edge, are the costal, the sub-costal, the 

 median, the sub-median and internal. Sometimes the median divides 

 into two. The front or costal vein is undivided ; the sub-costal and 

 median are divided into several branches ; the sub-median and inter- 

 nal are generally simple. 



The piercer mentioned above is properly an ovipositor, 

 and is in some cases a jointed tube, and is used for con- 

 ducting eggs into holes where they are to be left to be 

 hatched ; in other cases it is a scabbard containing a cen- 

 tral borer, or saws in some cases, which are used in making 

 holes in which eggs are to be deposited. The sting with 

 which many insects, as bees and wasps, are provided is 

 merely a modified ovipositor, and consists of a sheath cov- 

 ering a sharp instrument for inflicting wounds, and con- 

 necting with it inside of the body is a sac of poison. 



The digestive system of insects is quite complicated. It 

 consists of a mouth variously modified in the different 

 groups, a pharynx, a gullet, a first stomach or crop, a sec- 

 ond stomach or gizzard, a small intestine, etc. In some 

 kinds the mouth parts are modified for biting and chew- 

 ing purposes; in others they are so modified as to be 

 adapted for sucking organs. The parts called mandibles 



Mandibles of different Insects. 



A, Beetle ; B. Grasshopper ; C> Dragon-fly ; D' Wasp ; E- Bedbug, (in which 

 mandibles, maxilla, and labium are united to form the beak or jointed sucker) ; F- 

 Musquito (with bristle-like mandibles) ; C- Cock-chafer. 



are situated on each side of the mouth opening, and they 

 vary greatly in form and size. They usually consist of 



