120 



ENTOMOLOGY 



stomach, however, is absorption, which is effected by the 

 general epithelium. Physiologically, the so-called stomach of 

 an insect is quite unlike the stomach of a vertebrate, being more 

 like an intestine. 



Proctodaeum. At the anterior end of the hind intestine 

 there is usually a pyloric valve, which prevents the contents of 

 the intestine from returning into the stomach. This valve may 

 operate by means of a sphincter, or constricting, muscle, or 

 may, as in Collembola (Fig. 144), con- 

 sist of a backward-projecting circular 

 ridge, or lip, which closes upon pressure 

 from behind. 



In its primitive condition the hind 

 intestine is a simple tube (Fig. 144). 

 Usually, however, it presents two or 

 even three specialized regions, namely 

 and in order, ileum, colon and rectum 

 (Fig. 145). The hind intestine varies 

 greatly in length and is frequently so 

 long as to be thrown into convolutions 

 (Fig. 150). The ileum is short and 

 stout in grasshoppers (Fig. 145) ; long, 

 slender and convoluted in many carniv- 

 orous beetles ; and quite short in cater- 

 pillars and most other larvae; its func- 

 tion is absorption. The colon, often 

 absent, is evident in Orthoptera and 

 Lepidoptera and may bear (Benacus, 

 Dytiscus, Silphidse, Lepidoptera) a con- 

 spicuous caecal appendage (Figs. 148, 150) of doubtful func- 

 tion, though possibly a reservoir for excretions! The colon 

 contains indigestible matter and the waste products of diges- 

 tion, including the excretions of the Malpighian tubes. The 

 rectum (Fig. 145) is thick-walled, strongly muscular and often 

 folded internally. Its office is to expel excrementitious matter, 

 consisting largely of the indigestible substances chitin, cellulose 



Digestive system of Belos- 

 toma.- c, caecum; i, ileum; 

 m, mid intestine; mt, Mal- 

 pighian tubes; r, salivary 

 reservoir; s, salivary gland. 

 After LOCY, from the 

 American Naturalist. 



