ENTOMOLOGY 



In most insects a cardiac valve guards the entrance to the stomach, 

 preventing the return of food to the gullet. This valve (Figs. 146, 151) 



cm 



FIG. 150. Alimentary tract of a moth, Sphinx, c, food reservoir; cl, colon; cm, 

 caecum; , ileum; m, mid intestine; mt, Malpighian tubes; o, oesophagus; r, rectum; s, salivary 

 gland. After WAGNER. 



is an intrusion of the stomodaeum into the mesenteron, forming a circu- 

 lar lip which permits food to pass backward, but closes upon pressure 

 from behind. 



Mesenteron. The ventriculus, otherwise known as the mid intestine, 

 or stomach, is usually a simple tube of large caliber, 

 as compared with the oesophagus or intestine, and into 

 the ventriculus may open glandular blind tubes, or 

 gastric caca (Figs. 147, 148) ; these, though numerous 

 in some insects, are commonly few in number and 

 restricted to the anterior region of the stomach. The 

 gastric caeca of Orthoptera secrete a weak acid which 

 emulsifies fats, or one which passes forward into the 

 crop, there to act upon albuminoid substances. In 

 the stomach the food may be acted upon by a fluid 

 secreted by specialized cells of the epithelial wall. 

 In various insects, certain cells project periodically 

 into the lumen of the stomach as papillae, which by a 

 process of constriction become separated from the 



PIG. 151. Cardiac r 



valve of young muscid parent cells and mix bodily with the food. Thisphe- 

 nomenon takes place in the larva of Pty chapter a (van 



valve, in an older Gehuchten), also in nymphs of Odonata (Needham). 



larva the valve pro- ,. " / 



jects into the mid in- and is probably of widespread occurrence among m- 



sects - The chief function of the stomach is absorp- 

 tion, 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 kind intestine there is 

 usually a pyloric valve, which prevents the contents of the intestine 



