FORE-GUT OF CORYDALIS CORNUTUS L. 585 



oesophagus to the gizzard. This contraction is brought about by 

 the circular and longitudinal muscles. On cutting the lateral 

 muscles of the pharynx the expansion preceding the wave-like 

 contraction ceases, although the latter movement continues. 



The oesophagus 



The oesophagus, except for a gradual increase in size, extends 

 as a straight, cylindrical tube from the pharynx to the middle 

 of the second thoracic segmeilt where it passes into the gizzard 

 (fig. l,k). Viewed externally it presents no important structural 

 characters. The arrangement of the circular and longitudinal 

 muscles, to be discussed more in detail later, can readily be ob- 

 served in the freshly opened larva (fig. 3). On each side of the 

 oesophagus runs a large nerve (fig. 3, n), a branch of the so-called 

 visceral nervous system. Close to each nerve a tracheal branch 

 runs forward as previously described in discussing the respiratory 

 system. 



In histological structure the oesophagus, as in all insects so 

 far studied, presents the usual three layers: (1) the epithelium 

 with its intima; (2) the basement membrane lying directly 

 beneath the epithelium; (3) the muscular layer consisting of cir- 

 cular and longitudinal fibers. 



The epithelium with its intima and the basement membrane 

 are thrown into numerous irregular folds (fig. 8) . At times these 

 folds almost completely close the lumen. The folding allows 

 considerable contraction or distension of the oesophagus and does 

 not, I think, function in the reduction of the food. The resiliency 

 of the intima aids materially in the distension of the oesophagus 

 for the reception of food. 



The epithelium consists of a thin layer of flat cells with boun- 

 daries very indistinct or lacking. The nuclei are oval in outline, 

 with their long axes usually parallel to the basement membrane 

 (fig. 17). The cytoplasm presents a granular appearance. This 

 part of the fore-gut may secrete a digestive fluid, as Plateau 

 ('74) found in several species of insects examined by him but I 

 found no evidence of it. Its chief function seems to be the for- 



