9 6 



ENTOMOLOGY 



ward-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 in- 

 testine varies greatly in length and is frequently so long as to be thrown 

 into convolutions (Fig. 150). The ileum is short and stout in grass- 

 hoppers (Fig. 145); long, slender and convoluted in many carnivorous 

 beetles; and quite short in caterpillars and most other larvae; its func- 

 tion is absorption. The colon, often absent, is evident in Orthoptera and 



r-... 



FIG. 150. Digestive system of Bclos- 



FIG. 151. Wall of mid intestine of silk 



toma. c, caecum; i, ileum; m, mid intestine; worm, transverse section. &, basement mem- 

 mt, Malpighian tubes; r, salivary reservoir; brane; c, circular muscle; i, intima; I, longi- 

 s, salivary gland. After LOCY, from the tudinal muscle; n, n, nuclei of epithelial 



A merican Naturalist. 



cells; s, secretory cell. 



Lepidoptera and may bear (Benacus, Dytiscus, Silphidae, Lepidoptera) a 

 conspicuous csecal appendage (Figs. 148, 150) of doubtful function, 

 though possibly a reservoir for excretions. The colon contains indigest- 

 ible matter and the waste products of digestion, 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 excrementi- 

 tious matter, consisting largely of the indigestible substances chitin, 

 cellulose and chlorophyll. The rectum terminates in the anus, which 

 opens through the last segment of the abdomen, always above the genital 

 aperture. 



