22 



from the mouth to the anus, and is remarkable on account 

 of its extremely simple structure. AVith the exception of 

 a pair of salivary glauds there are no accessory organs in 

 association with it. 



The fore-gut consists of the pharynx and the 

 oesophagus. The pharynx is a capacious cavity and 

 occupies about one-sixth of the total length of the fore- 

 gut. Its dorsal or anterior wall is formed by the labrum 

 and its ventral wall or floor by the labium or lower lip 

 (Plate III., fig. 27). The pharynx is evaginated into four 

 backwardly directed pockets, two on either side for the 

 reception of the mandibles and first maxillse (Plate lY., 

 fig. -35). The lingua occupies a median position in the 

 floor of the pharynx, and the maxillulpe are closely applied 

 to the upper surface of the former. 



The oesophagus is a narrow tube of a very uniform 

 calibre throughout its length (Plate III., fig. 27). At the 

 point where it joins the mid-gut it projects for a short 

 distance into the cavity of the latter in the form of a 

 papilla (Plate III., fig. 28). The lumen of the oesophagus 

 is roughly H-shaped in transverse section, owing to four 

 inwardly directed bulgings of its epithelial walls (fig. 29). 



The walls of the fore-gut consist of three laN^ers ; the 

 innermost is a chitinous intima, the middle one is an 

 epithelium, and the outer one is muscular. The chitinous 

 lining, which is secreted by the underlying epithelial 

 layer, is continuous with the cuticle of the integument. 

 It is very thin and, with the exception of a few scattered 

 tooth-like projections in the region of the pharnyx and 

 the anterior part of the oesophagus, its surface is perfectly 

 smooth. Whether the epithelial layer is of the nature of a 

 true epithelium or not is uncertain. It has not been 

 possible to detect any cell-boundaries even after a 

 prolonged treatment of sections with suitable staining 



