ANATOMY AND PHYSIOLOGY 



mid intestine, or stomach, is usually a simple tube of large 

 caliber, as compared with the oesophagus or intestine, and into 



FIG. 148. 



cl 



FIG. 149. 



* cm 



Alimentary tract of a moth, Sphinx, c, food reservoir; cl, colon; cm, caecum; i, ileum; 

 in, mid intestine; mt, Malpighian tubes; o, oesophagus; r, rectum; s, salivary gland. 

 After WAGNER. 



the ventriculus may open glandular blind tubes, or gastric 

 cceca (Figs. 145, 146) ; these, though 

 numerous in some insects, are commonly 

 few in number and restricted to the ante- 

 rior 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 epithe- 

 lial 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 

 parent cells and mix bodily with the food. 

 This phenomenon takes place in the larva 

 of Ptychoptera (van Gehuchten), also in 

 nymphs of Odonata (Needham), and is 

 probably of widespread occurrence among 

 insects. The chief function of the 



Cardiac valve of young 

 muscid larva, o, oesoph- 

 agus; p, proventriculus; 

 v, valve. In an older 

 larva the valve projects 

 into the mid intestine. 

 After KOWALEVSKY. 



