IO4 



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) 



mt 



cl 



' cm 



PIG. 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 cceca (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 

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

 ^ rV proventricuiu? U ^ ; nomenon takes place in^ the larva of Ptychoptera (van 

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



larva the valve pro- . . 7 .. , 



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

 *estine. After KOWA- sectSi The chief function of the stomach is absorp- 



LEVSKY. 



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 hind intestine there is 

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



PIG. 151. Cardiac 



