THE ILEUM AND THE COLON 317 



The ileum Though in most insects slender, and therefore called 



the small intestine, the ileum is in locusts (Fig. 298) and grasshop- 

 pers (Anabrus, Fig. 299) as thick as the stomach. In many carnivo- 

 rous beetles (Dyticus, Fig. 320, il, and Necrophorus) it is very 

 long, but rather slender and short in the Carabidse and Cicindelidae, 

 as well as those insects whose food is liquid, such as Diptera. In 

 the Lepidoptera it varies in length, being in Sphinx quite long and 

 bent into seven folds (Fig. 309), while it is very short in the Psocidse, 

 Chrysomelidse, and Tenthredinidse. 



In the locust the ileum is traversed by six longitudinal folds with 

 intervening furrows ; outside of each furrow is a longitudinal muscu- 

 lar band. Seen from the inner surface the epithelium has an unusual 

 character, the cells in the middle of each of the flat folds being quite 

 large, polygonal in outline, while towards the furrows the cells be- 

 come very much smaller. The walls are double when seen in trans- 

 verse section, the inner layer consisting of epithelial cells resting on 

 connective tissue, the outer layer formed of circular muscles. The 

 cuticula is thin, but probably chitinous; it resembles that on the 

 gastro-ileal folds, except that there are no spinules, but unlike 

 the cuticula of the stomach it extends equally over the folds and the 

 furrows. (Minot.) In the cockroach the junction of the small in- 

 testine with the colon is abrupt, a well-developed annular fold 

 assuming the nature of a circular valve. (Miall and Denny.) 



The gastro-ileal folds In the locust the intestine is separated 



from the chylific stomach by what Minot calls u the gastro-ileal 

 folds," which form a peculiar valve. The urinary vessels open just 

 underneath and in front of this valve. In Melanoplus, and probably 

 in the entire family of Acrydiidse, they are indicated as " dark spots, 

 round in front and lying at the anterior end of the ileum so as to 

 form a ring around the interior of the intestine." They are 12 in 

 number, and all alike. They are pigmented and round in front 

 where they are broadest and stand up highest ; they narrow down 

 backwards, the pigment disappears, and they gradually fade out into 

 the ileal folds. Directly beneath them, and just at the posterior end 

 of the stomach, there is a strong band of circular striated muscular 

 fibres. The epithelium of these folds is covered with minute conical 

 spines, which are generally, but not always, wanting between the 

 folds. (Minot.) 



The colon This section of the intestine (Fig. 319) is sometimes 



regarded as a part of the rectum. In the locust the six longitudinal 

 folds of the ileum are continued into the colon, but their surface, 

 instead of being smooth as in the ileum, is thrown up into numerous 



