370 PHYSIOI-OGY. 



nutrimental canal throughout the animal kingdom. They thus repre- 

 sent in their crop and proventriculus the form of the canal of birds, 

 and by means of the blind appendages of the duodenum they are like- 

 wise connected with the fishes. 



223. 



In all the higher and in many of the lower animals, namely, the 

 Mollusca, the formation of the chyle is produced by the addition of a 

 peculiar fatty alkaline fluid, namely, the gall, which is secreted by a 

 large lobate gland, called the liver, the duct of which empties itself 

 into the duodenum, sometimes behind the pylorus, but in general in the 

 vicinity of the opening of the ventral salivary glands. The object of 

 this fluid appears to be to decrease the acidity of the chyme, and 

 then by the intermixture of its component parts to prevent a preju- 

 dicial corrupt decomposition of the food upon passing through the 

 intestinal canal ; to transmit the fat in suspension, in which it is more 

 readily absorbed; and to assimilate the nutriment by means of the gall 

 and other animal matters it contains ; audjastly to stimulate the peris- 

 taltic motion *. We may now ask if an analogue of these glands is to 

 be found in insects, and whether its secretion when it exists is of such 

 influential effect as the gall in general. 



With respect to the existence in insects of such glandular secretory 

 organs which empty themselves into the intestinal canal, we may 

 observe, that but one kind of them is found, which is peculiar to all 

 excepting Chermes and Aphis, and this is the above described ( 111) 

 biliary vessels. All other secreting organs which are found in the 

 intestine of insects are peculiar to certain orders and families O7ily. 

 We have characterised them above as salivary organs, and given a 

 detailed account of their form and presence ( 112). 



These gall vessels are actually gall-secreting organs, according to 

 Cuvier, Posselt, Ramdohr, Carus, and the earlier opinions of Treviranus 

 and Meckel. This opinion may be supported by 



1. The general form of the secreting organs in insects. 



2. By their situation, and by their insertion in the intestinal canal 

 corresponding with that of the gall-secreting organs of other 

 animals. 



* Gmelin's Theor. Chimie, vol. ii. part ii. p. 1517. The result of the comprehensive 

 experiments of Tiedcmann and Gmelin upon digestion. 



