ANATOMY AND PHYSIOLOGY 



93 



most specialized insects exhibit the following modifications (Figs. 145, 

 146) of the three primary regions : 



Fore intestine (stomodceum) : mouth, pharynx, oesophagus, crop, pro- 

 ven triculus (gizzard), cardiac valve. 



M id intestine (mesenteron) : ven triculus (stomach) . 



Hind intestine (proctodceum) : pyloric valve, ileum, colon, ~fcc turn, 

 anus. 



Stomodaeum. The mouth, the anterior opening of the food canal, is 

 to be distinguished from the pharynx, a dilatation for reception of food. 

 In the pharynx of mandibulate insects the food is acted upon by the 

 saliva; in suctorial forms the pharynx acts as a pumping organ, in the 

 manner already described. 



The oesophagus is commonly a simple tube of small and uniform caliber, 

 varying greatly in length according to the kind of insect. Passing be- 

 tween the commissures that connect the brain with the subcesophageal 



FIG. 145. Alimentary tract of a grasshopper, Melanoplus differential-is, c, colon; cr, 

 crop; gc, gc, gastric caeca; i, ileum; m, mid intestine, or stomach; mt, Malpighian, or kidney, 

 tubes; o, oesophagus; p, pharynx; r, rectum; s, salivary gland of left side. 



ganglion (Fig. 113), the oesophagus leads gradually or else abruptly into 

 the crop or gizzard, or when these are absent, directly into the stomach. 

 In addition to its function of conducting food, the oesophagus is sometimes 

 glandular, as in the grasshopper, in which it is said to secrete the "mo- 

 lasses" which these insects emit. 



The crop is conspicuous in most Orthoptera (Fig. 145) and Cole- 

 optera (Fig. 146) as a simple dilatation. In Neuroptera (Fig. 147) its 

 capacity is increased by means of a lateral pocket the food reservoir; 

 this in Lepidoptera, Hymenoptera and Diptera is a sac (Fig. 148, c) 

 communicating with the oesophagus by means of a short neck or a long 

 tube, and serving as a temporary receptacle for food. In herbivorous 

 insects the crop contains glucose formed from starch by the action of 

 saliva or by the secretion of the crop itself; in carnivorous insects this se- 

 cretion converts albuminoids into assimilable peptone-like substances. 



Next comes the enlargement known as the proventriculus, or gizzard, 



