DIGESTION IN INSECTS. 317 
kaline fluid, probably aiding in digestion. In tne stomach 
{ventriculus) 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 tne 
‘*brain.”? The brain rests upon the oesophagus, whence its 
name, supra-cesophageal ganglion. From the brain arise the 
large, short, optic nerves (Fig. 276, not lettered, but repre- 
