292 PERIPATUS, MYRIOPODS, AND INSECTS. 



to adjacent parts. There are three pairs of ganglia in the 

 thorax, and six in the abdomen, of which the last is the 

 largest. From the oesophageal commissures two visceral 

 nerves are given off, which form in a somewhat complex 

 manner the innervation of gullet, crop, and gizzard. Besides 

 the large compound eyes, there are other sensory structures 

 — some of the hairs on the skin, the maxillae (to some 

 extent organs of taste), the antennae (tactile and olfactory), 

 the anal cerci (tactile), and possibly the oval white patches 

 on the head. 



Alimentary system. — (i) The fore-gut (stomodaeum) is 

 lined by a chitinous cuticle continuous with that of the 



outer surface of the 

 body. It includes 

 — (a) the buccal 

 or mouth cavity, 

 in which there 

 is a tongue - like 

 ridge, and into 

 which there opens 

 the duct of the 

 salivary glands ; (6) 

 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 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 chitinous 

 cuticle. It is convoluted and divided into narrow ileum, 

 wider colon, and dilated rectum with six internal ridges. 



Respiratory system. — The tracheal tubes, which have 



Fig. 129. — Transverse section of insect. — 

 After Packard. 



\/t., Heart ; g., gut ; «., nerve-cord ; st., stigma ; tr., 

 trachea; w., wing;./, femur of leg. 



