590 ROBERT MATHESON 



The oesophageal valve 



In Corydalis the oesophageal valve is not so marked as that 

 found in many other insects. It is formed by the invagination 

 of the fore- into the mid-gut. This invagination is short and is 

 lined internally by a thick intima which is folded into fowr large, 

 tooth-like ridges (fig. 12). Externally to the basement mem- 

 brane lie the circular muscles. Outside of these are found longi- 

 tudinal muscles, continuations forward of the mid-gut fibers. 

 They group themselves as they pass between the caeca and most 

 of them are attached to the four chitinous ridges. Others con- 

 tinue forward and are attached at various points behind the giz- 

 zard. These longitudinal muscles, besides their function of 

 opening the lumen, undoubtedly serve to hold the valve in place 

 and prevent its evagination by the pushing back of any con- 

 gested food in the mid-gut. The epithelium lining the valve is 

 of the ordinary type found in the fore-gut except for a group of 

 cells located at the point of union between the fore- and mid-gut 

 epithelium (fig. 10, g.e.). These cells clearly present a glandular 

 appearance but stand in marked contrast to the glandular epithe- 

 lium of the mid-gut (fig. 10, ep.). What the particular function 

 of this group of cells is would be difficult to conjecture as I do 

 not find any peritrophic membrane and they do not show any of 

 the characteristics of an imaginal ring as described for so many 

 insects. 



METAMORPHOSIS OF THE FORE-GUT 



Pupation 



The mature larvae leave the water in the latter part of May or 

 June and pupate in cavities under stones near the stream. Davis 

 ('03) found that the pupal life lasted from seven to fourteen days, 

 the average being nine days. The larvae from which my material 

 was obtained were received about the 23d of May, 1910, and were 

 placed in a dish with a small amount of water. The dish was then 

 placed in a box of moist earth over the surface of which were 

 placed several flat stones. The larvae immediately crawled out 



