DIQESTION IN INSECTS. 317 



kaline fluid, probably aiding in digestion. In tne stomach 

 (Yentriculus) the portion of the food which has resisted the 

 action of the crop is submitted to the action of a neutral or 

 alkaline liquid, never acid, secreted by special local glands 

 or by the lining epithelium. In the ileum and colon ac- 

 tive absorption of the liquid portion of the food takes place, 

 and the intestine proper (ileum and colon) is thus the seat 

 of the secondary digestive phenomena. The reaction of the 

 secretion is neutral or alkaline. The rectum is the ster- 

 coral reservoir. It may be empty or full of liquids, but 

 never contains any gas. The liquid products secreted by 

 the urinary tubes are here accumulated, and in certain cir- 

 cumstances here deposit the calculi or crystals of oxalic,, 

 uric, or phosphatic acid. Insects, says Plateau, have no 

 special vessel to carry off the chyle, such as the lacteals or 

 lymphatics of vertebrates ; the products of digestion — viz., 

 salts in solution, peptones, sugar in solution, and emulsion- 

 ized greasy matters — pass through the fine coatings of the 

 digestive canal by osmosis, and mingle outside of this canal 

 with the currents of blood which pass along the ventral and 

 lateral parts of the body. 



Into the pyloric end of the stomach empty the urinary 

 tubes, their secretions passing into the intestine. These are 

 organs exclusively depuratory and urinary, relieving the 

 body of the waste products. The liquid which they secrete 

 contains urea (?), uric acid, and urates in abundance, hip- 

 puric acid (?), chloride of sodium, phosphates, carbonate of 

 lime, oxalate of lime in quantity, leucine, and coloring mat- 

 ters. 



The nervous system of the locust, as of other insects, con- 

 sists of a series of nerve-centres, or so-called brains (ganglia), 

 which are connected by two cords (commissures), the two 

 cords in certain parts of the body in some insects united into 

 one. There are in the locust ten ganglia, two in the head, 

 three in the thorax, and five in the abdomen. The first 

 ganglion is rather larger than the others, and is called the 

 *' brain." The brain rests upon the oesophagus, whence ita 

 name, supra-cesophageal ganglion. From the brain arise the 

 large, short, optic nerves (Fig. 376, not lettered, but repra- 



