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. Sc Nat. ii. 473. 



VOL. II. P 



