OF DIGESTION. 367 



efforts was thrown np, whereupon the caterpillar died. After this, air 

 in the shape of bladders broke out. This air appears to be constantly 

 found in the stomach during digestion, and is probably partially 

 swallowed with the food, and is partly evolved from the food in the 

 stomach. The first takes place, according to Rengger, that the gastric 

 juice which is spirted forth as a defence may be the more easily ejected, 

 yet the constant biting and swallowing small pieces of leaves necessarily 

 occasions the passage of some air into the stomach. During the pupa 

 state, the intestine contains only air, or even nothing : we also find in 

 perfect insects, for example, in the Ephemera, Libdhdce, Grylli, &c., 

 much air in the stomach and the whole intestinal canal. 



The digestion of fluids which haustellate insects imbibe, takes place, 

 doubtlessly, in the same manner as the firmer manducated nutriment, 

 with the alterations only which arise from the difference of food. The 

 more elaborated the juices are, the more simple is the structure of the 

 intestinal canal, whence it follows that the digestion of the nectar of 

 flowers takes place in the Hymcnoptera in a single cylindrical, but 

 compact, transversely ridged duodenum, whence the chyme, together 

 with the addition of the secretion of the many biliary vessels, passes 

 into the true ilium. In the bugs, this simple duodenum, as the above 

 description of their digestive apparatus ( 105) has shown, is separated 

 into several intestinal divisions, the first of which corresponds with the 

 crop, the second with the proventriculus, and the third with the true 

 duodenum. In addition to this great perfection of the chymifying 

 portion of the intestinal canal, we must include the long and multi- 

 farious salivary vessels as preparatory organs, which very much facilitate 

 the progress of digestion by the contribution of their secretion. The 

 juices are thereby made capable of assimilation, and the assimilating 

 portion is absorbed by the parietes of the ilium. It arises thence, also, 

 that that portion of the intestine which lies beyond the duodenum is, 

 at least in the bugs, extraordinarily short, whereas in the Hymenoptera 

 and in the flies it is of the same length, or, as in the Lepidoptera, even 

 longer. The smallness of the stomach connected with the duodenum 

 in the Lepidoptera, makes us surmise that they take but little, or, 

 indeed, many of them in their perfect state no food at all, or that, 

 as their food consists of the nectar of flowers, it requires but little 

 change. Thence their small stomach and long narrow ilium ; and, 

 next to the saliva, the secretion of the biliary vessels may contribute 

 considerably to the transformation of this honey. Among the Coleoptera 



