26 



ECONOMIC ENTOMOLOGY 



Fig. 30. — Dorsal view of ali- 

 mentary canal of the larva of the 

 budmoth {Tmetocera ocellana). 

 Ph., Pharynx; Oes., oesophagus; 

 SM., suspensory muscles; Tr., vis- 

 ceral tracheal of left side; MT., 

 Malpighian tubules; Mes., mesen- 

 teron; Int., small intestine; In., 

 intestinal nerve; R., rectum. 



directly into the stomach which is long. 

 Further digestion occurs here through 

 the action of secretions of the c(Bcal tubes, 

 often called the gastric cceca, which con- 

 sist of glandular pouches emptying into 

 the anterior end of the stomach. Most 

 of the digested food is here absorbed 

 and passes into the circulation. Pos- 

 terior to the stomach is the intestine 

 which consists of three parts — ileum, 

 colon, and rectum. Into the ileum open 

 the Malpighian tubes which are excretory 

 in function, similar to the kidneys of 

 higher animals. The undigested portions 

 of food are expelled through the rectum 

 and anus. 



Some variations may be noted. The 

 oesophagus is long in those insects that 

 suck their food, and short in herbivo- 

 rous forms. In sucking insects the giz- 

 zard may be absent, and the crop is often 

 a side pocket of the oesophagus (Fig. 30). 



Structurally, the wall of the alimen- 

 tary canal consists of: 



1. An epithelial layer of cells which 

 secrete the intima or lining layer. 



2. The delicate basement membrane. 



3. Circular muscles. 



4. Longitudinal muscles, which aid in 

 constricting and enlarging the canal 



(Fig. 31)- 



From an embryological point of view 

 the alimentary tract consists of three 

 primary regions: 



1. The Stomodceum, embracing the 

 fore part as far as the stomach. 



2. The Mesenteron, or mid-intestine 

 embracing the stomach, and 



