28 TRANSFORMATIONS OF INSECTS. 
and evolve the fluid from their cellular structures. But the 
glands of the herbivorous insects are not visible on the outside 
of the stomach, and are contained in its walls instead. The 
secretion of the gastric juice is determined by the stomach being 
more or less filled, just as in man, and when this is the case 
the little glands give forth their cellular and fluid contents in 
great abundance. When the stomach is empty, the digestive 
fluid is very scanty, loses its acidity, and is even occasionally 
alkaline. Now this repeated secretion of a special acid fluid 
which continues during the life of the caterpillar—for it is con- 
stantly eating, except when moulting, or perhaps when in the 
dark—is discontinued during the chrysalis state, and the glandular 
structures become atrophied and often lost altogether, especially 
in those perfect insects which do not take food. 
The intestine follows the stomach, and its commencement is 
indicated by a constriction and by the attachment of the liver 
canals; the constriction has a fold internally which prevents the 
too rapid passage of the food out of the stomach into the intestine. 
It is very remarkable that the variation in the length and shape 
of the intestine should not depend upon the food or upon the 
habits of the insect, and that it should not differ much in these 
respects in the larva, the chrysalis, and the perfect insect. The 
intestinal canal ends in pocket-shaped enlargements or in simple 
odd-shaped swellings, one of which is shown in the case of 
Dytiscus. 
The salivary glands are situated on each side of the cesophagus, 
and look like twisted tubes, or sacs with cellular walls. Usually 
there are two or three pairs of glands, and they are of two kinds. 
For instance, in the grasshopper, whose salivary glands are large, 
they consist of one pair of bunches of bag-like swellings, and of 
another pair of elongated tubes. Both kinds secrete special 
fluids, and their admixture is effected in the canal which is 
common to the two sorts of glands, and the saliva flows straight 
into the mouth. The saliva is slightly alkaline, and not only 
lubricates the morsel during deglutition, but assists in the diges- 
tion of it also. In the Lepidoptera, or butterfly tribe, the salivary 
glands are simple elongated tubes, which are largely developed in 
the caterpillar, and more or less atrophied in the chrysalis and 
