STRUCTURES IMPLICATED IN METAMORPHOSIS. 2/ 



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 bv 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, 



