STRUCTURES IMPLICATED IN METAMORPHOSIS. 
27 
be distinguished in insects which are great eaters, such as the 
crickets, grasshoppers, and locusts, as well as in those which make 
some provision for the larvae which are to come after them. 
Many have the power of disgorging their food from the crop ; 
and the bee empties the honey which it has collected from its 
favourite flowers out of this receptacle into the cells of the hive. 
Sometimes the crop forms a side pocket to the gullet, and becomes 
almost an appendix. This is the case in the Lepidoptera (the 
butterflies and moths). Occasionally in the Diptera (the fly tribe) 
the sac or crop, when thus more or less separated, is provided 
with a long neck which opens into the gullet close to the mouth. 
When thus formed it has something to do with the suction of food, 
but the mechanism by which it acts as a sucking-pump is not 
exactly understood. 
Usually the stomach follows upon the oesophagus, but a con- 
striction is noticed in most insects at the end of the gullet, which 
is made up of hard muscular tissue ; it is the gizzard, and its 
inside is thrown into long folds more or less dense, and is often 
covered with hard growths which triturate the semi-masticated 
food before it passes into the stomach. 
A gizzard only being necessary to herbivorous and carnivorous 
insects is not found in those which live by suction or whose food 
does not require unusual breaking up. 
The stomach varies greatly in its length and general dimen- 
sions ; sometimes, as in the grasshopper, it is a large and some- 
what heart-shaped sac terminating in the form of a tubular canal, 
and its walls are thick. More frequently it is elongated, and is 
either smooth or covered with a multitude of such glands, as in 
the water beetles and other carnivorous kinds. It is the principal 
organ of digestion, and the food is mixed there with the gastric 
juice. This liquid, always acid when digestion is going on, 
possesses the same qualities as that of the higher animals, and 
reduces the aliments into a pulp, and finally into chyme. The 
gastric juice is more freely secreted in some insects than in others, 
and is most abundant in those which live upon animal food. 
The glands which produce the juice in these carnivorous insects 
are very well developed and may be recognised as tiny blunt 
projections upon the outside of the stomach ; they are hollow, 
