DIGESTIVE ORGANS OF INSECTS. 209 



In some insects these tubes are of larger dia- 

 meter than in others ; and in many of the Or- 

 thoptera, as we shall presently see, they open 

 into large receptacles, sometimes more capacious 

 than the stomach itself, which have been sup- 

 posed to serve the purpose 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 

 proportion 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 mem- 

 brane, which constitute 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 



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

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

 gress of assimilation. Ann. 3c. Nat. ii. 478. 

 VOL. II. P 



