DIGESTIVE ORGANS OF INSECTS. 185 



we shall presently see, they open into large recep- 

 tacles, sometimes more capacious than the stomach 

 itself, which have been supposed to serve the pur- 

 pose of reservoirs of the biliary secretion ; pouring 

 it into the stomach on those occasions only when it 

 is particularly wanted for the completion of the 

 digestive process.* 



The distinction into small and great intestine is 

 more or less marked, in different insects, in pro- 

 portion to the quantities of food consumed, and to 

 its vegetable nature; and in herbivorous tribes, 

 more especially, the dilatations in the lower part of 

 the canal are most conspicuous, as well as the 

 duplicatures of the inner membrane, which consti- 

 tute imperfect valves for retarding the progress of 

 the aliment. It is generally at the point where 

 this dilatation of the canal commences, that a second 

 set of hepatic vessels is inserted; having a structure 

 essentially the same as those of the first set ; but 

 generally more slender, and uniting into a small 

 number of ducts before they terminate. The 

 number and complication of both these sets of 

 hepatic vessels, appear to have some relation to 

 the existence and developement of the gizzard, and 

 consequently also to the nature and bulk of the 

 food. Vessels of this description are, indeed, con- 

 stantly found in insects ; but it is only where a 

 gizzard exists, that two sets of these secreting 

 organs are provided ; and in some larvae, remark- 



* A doubt is suggested, by Leon Dufour, whether the hquid 

 found in those pouches is real bile, or merely aliment in the progress 

 of assimilation. Ann. Sc. Nat. ii. 478. Many of the Hemiptera 

 possess a gall-bladder, which is either single or double, and which 

 opens into the cavity of the large intestine. 



