296 PERIPATUS, MYRIOPODS, AND INSECTS. 



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 Systetti. — (i) The fore gut (stomatodasum) 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 ; {b) the narrow 

 gullet or oesophagus ; (c) the swollen crop ; {d) the gizzard 



Fig. 96. — Transverse section of Insect. (After Packard.) 



h, Heart ; i'', gut ; «, nerve cord ; st^ stigma ; z'r, trachea ; 7y, 

 wing ; f, femur of leg. 



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 recep- 

 tacle. 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 



