n8 



ENTOMOLOGY 



FIG. 147. 



The crop is conspicuous in most Orthoptera (Fig. 145) and 

 Coleoptera (Fig. 146) as a simple dilatation. In Neuroptera 

 (Fig. 147) its capacity is increased by 

 means of a lateral pocket the food reser- 

 voir; this in Lepidoptera, Hymenoptera 

 and Diptera is a sac (Fig. 148, c) commu- 

 nicating with the oesophagus by means of 

 a short neck or a long tube, and serving as 

 a temporary receptacle for food. In her- 

 bivorous insects the crop contains glucose 

 formed from starch by the action of saliva 

 or the secretion of the crop itself ; in car- 

 nivorous insects this secretion converts 

 albuminoids into assimilable peptone-like 

 substances. 



Next comes the enlargement known as 

 the provcntricnlns, or gizzard, which is 

 present in many insects, especially Orthop- 

 tera and Coleoptera (Fig. 146), and is 

 usually found in such mandibulate insects 

 as feed upon hard substances. The pro- 

 ventriculus is lined with chitinous teeth or 

 ridges for straining the food, and has 

 powerful circular muscles to squeeze the 

 food back into the stomach, as well as 

 longitudinal muscles for relaxing, or open- 

 ing, the gizzard. Some authors maintain that the proventricu- 

 lus not only serves as a strainer, but also helps to comminute 

 the food, like the gizzard of a bird. 



In most insects a cardiac valve guards the entrance to the 

 stomach, preventing the return of food to the gullet. This 

 valve (Figs. 144, 149) is an intrusion of the stomodaeum into 

 the mesenteron, forming a circular lip which permits food to 

 pass backward, but closes upon pressure from behind. 



Mesenteron. The ventriculus, otherwise known as the 



Digestive system of 

 Myrmeleon larva. c, 

 caecum; cr, crop; m, mid 

 intestine; mt, Malpighian 

 tubes; s, spinneret. 

 After MEINERT. 



