330 PHYL UM AR THRO POD A. 



cavity, in which there is a tongue-like ridge, and into 

 which there opens the duct of the salivary glands ; () the 

 narrow gullet or oesophagus ; (c) the swollen crop ; (d) the 

 gizzard, with muscular walls, six hard cuticular teeth, and 

 some bristly pads. 



There is a pair of diffuse salivary glands on each side of the crop, and 

 between each pair of glands a salivary receptacle. The ducts of the 

 two salivary glands on each side unite ; the two ducts thus formed 

 combine in a median duct, and this unites with another median duct 

 formed from the union of the ducts of the receptacles. The common 

 duct opens into the mouth. 



(2) The mid-gut (mesenteron) is lined by endoderm. It 



FIG. 177. Transverse section of insect. After Packard. 



ft., Heart; g:, gut; ., nerve-cord; st., stigma; tr., trachea; ;., wing; 

 f., femur of leg. 



is short and narrow, and with its anterior end seven or 

 eight club-shaped digestive (pancreatic) outgrowths are 

 connected. 



(3) The hind-gut (proctodaeum) is lined by a chitin- 

 ous cuticle. It is convoluted and divided into narrow 

 ileum, wider colon, and dilated rectum with six internal 

 ridges. 



Bespiratory system. The tracheal tubes, which have 

 ten pairs of lateral apertures or stigmata, ramify through- 

 out the body, and have a spirally thickened chitinous 

 lining. 



Circulatory system. The chambered heart lies along 

 the mid-dorsal line of abdomen and thorax. It receives 

 blood by lateral valvular apertures from the surrounding 



