102 



ENTOMOLOGY 



tending along the axis of the body and consisting of three regions, 

 namely, fore, mid and hind gut. These regional distinctions are funda- 

 mental, as the embryology shows, for the middle region is entodermal 

 in origin and the two others are ectodermal, as appears beyond. 



There are many departures from this primitive condition, and the 

 most specialized insects exhibit the following modifications (Figs. 147, 

 148) of the three primary regions: 



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

 ven triculus (gizzard), cardiac valve. 



Mid intestine (mes enter on) : ven triculus (stomach). 



Ifind intestine (proctodaum) : pyloric valve, ileum, colon, rectum, 

 anus. 



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

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



FIG. 147. Alimentary tract of a grasshopper, Melanoplus differ entialis. c, colon; cr, 

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

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



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. Pass- 

 ing between the commissures that connect the brain with the subceso- 

 phageal ganglion (Fig. 115), 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 "molasses" which these insects emit. 



The crop is conspicuous in most Orthoptera (Fig. 147) and Cole- 

 optera (Fig. 148) as a simple dilatation. In Neuroptera (Fig. 149) its 

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

 this in Lepidoptera, Hymenoptera and Diptera is a sac (Fig. 150, c) 

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



