431 



it is roughly prismatic, and is triangular in section. Its walls 

 consist of three thickened epithelial plates (fig. 160), each 

 bent slightly inwards along its longitudinal median axis. The 

 three plates are lined internally by a very tough but elastic 

 chitin plate, which envelops them closely. The thickened 

 epithelia do not meet along the three angles of the prism, 

 and the intestinal epithelium here is much thinner. The 

 thick chitin plates are likewise absent here. 



Two setfi of muscles are present. There is an inner 

 circular which connects the two longitudinal edges of each 

 plate. A pull on them will evidently increase the angle at 

 which the plate is bent upon its longitudinal axis. Outside 

 the circular muscle layer lies a number of longitudinal fibres. 

 All are striated. 



The gizzard is then seen to be a very ingenious con- 

 trivance. In section its lumen is triradiate. A contraction 

 of the circular muscles causes increased bending of the three 

 chitin plates, and they move towards each other and tend to 

 close up the lumen. The resulting organ ought therefore to 

 prove a very efiicient masticatory structure for an insect in 

 which feeding is so reduced as in chalcid wasps. 



Tlie drum-shaped chamber immediately behind the gizzard 

 is smaller than the latter. Its walls are composed of minute 

 cells; these form a thickening several cells deep which pro- 

 jects into the stomach and forms the valve referred to above. 



The epithelial cells of the great stomach are large and 

 "brick-shaped" in appearance, measuring as long as 23ja. 

 The cytoplasm is granular and vacuolated; the nucleus very 

 large and faintly granulated. A great nucleolus may occa- 

 sionally be present. A distinct cuticular lining is absent. 



The small intestine (fig. 167) is lined by a single layer 

 of irregular elongated columnar cells, each with a very large 

 nucleus, and occasionally a great nucleolus; in places its 

 epithelium is very irregular, and the chitinous lining formed 

 within it presents these same irregularities. The irregularity 

 evidently allows of greater distension. There is in places a 

 highly developed coat of thick circular muscle fibres; longi- 

 tudinal fibres are also present, being long and spindle-shaped 

 and presenting a thickened nuclear swelling at their middle. 

 The fibres are, as usual, striated. 



Tlie epithelium of the dilated rectum (fig, 168) consists 

 of very large, rather flattened cells, frequently presenting a 

 great nucleolus. The usual chitin lining is present. The very 

 powerful muscle coating is in the form of a single layer of 

 broad, flattened, contractile plates presenting the usual 

 striations. 



