130 ANIMAL PHYSIOLOGY. [LESSON 37. 



600. It has been remarked that the crop is absent in insects pro- 

 vided with a suctorial mouth, but all these possess a peculiar organ 

 not found in other insects ; this is, sometimes, a bladder-shaped disten- 

 sion of the oesophagus ; in others it forms a distinct bag, which opens 

 into the oesophagus ; and in still another order it hangs appended to 

 the oesophagus by means of a long, thin duct, frequently far in front 

 of the stomach. 



601. This organ is the sucking, or pumping stomach ; its func- 

 tion does not consist in being a receptacle for nutriment, but in pro- 

 moting the procuration of it, by distending at the pleasure of the in- 

 sect, and by the rarefaction of the air contained in it, facilitating the 

 ascent of fluids in the terminal proboscis, and oesophagus. But the 

 action of this organ will be more fully explained hereafter. 



602. THE PROVENTB.ICULUS, or gizzard, is the third division of 

 the alimentary canal ; it is a small, narrow, and tubular cavity, fur- 

 nished with teeth, spines, or horny ridges. It lies in front of the 

 mouth (or commencement) of the stomach ; it is found in all insects 

 prone to feed on hard substances, which require thorough comminu- 

 tion previous to digestion. 



Externally it has a roundish or ovate appearance, and is more 

 distinctly muscular than any other portion of the intestinal canal. 



603. THE STOMACH is that portion of the canal which extends 

 from the end of the oesophagus, or of the crop, or of the gizzard, to 

 the opening of the evacuating ducts of the biliary vessels. Some 

 authors call it duodenum, because digestion commences in it, but from 

 the analogy of the higher animals it is probable that the stomach 

 ends prior to the connection with the bile vessels, and that their se- 

 cretion is poured into the first of the intestines proper. The subject, 

 however, is open to doubt, especially as we find commonly in the bi- 

 valve, and other Mollusca, that the bile is poured directly into the 

 stomach. 



The divisions from the stomach are fewer and more simple than 

 those which precede it ; with the exception of the colon they are 

 much narrower than the stomach, and more delicate in their struc- 

 ture. 



604. THE DUODENUM. When this intestine is present, it is sepa- 

 rated from the stomach by a distinct constriction, which is probably 

 a pylorus ; immediately beyond this the bile vessels enter the in- 

 testine. 



605. THE ILEUM. Wherever the duodenum is wanting, the ileum 

 follows immediately upon the stomach, from which it is also sepa- 



