REPRESENTATIVE INSECTS 



351 



gus to the crop and gizzard which are dilatations of the tract filling 

 a great portion of the thorax. The gizzard is muscular and lined 

 with chitinous ridges which strain the coarse particles of food and 

 prevent their entering the next division of the system, the stomach. 



\— Ab 



Fig 203 Nervous system of Rhomaelia microptera. Ah., first abdominal 



ganglion ; C, circumesophageal commissure ; Sp., supraesophageal ganglion ; Su., 

 subesophageal ganglion. (From White, General Biology. Tiie C. V. Mosby Co.) 



The food is acted upon in the stomach by the secretions of the gas- 

 tric caeca, which are glandular bodies opening into the anterior 

 end of the stomach. They secrete a weak acid which helps in the 



