FORE-GUT OF CORYDALIS CORNUTUS L. 591 



of the water and began burrowing under the stones. In a short 

 time many of them had completed their pupal chambers. 



The time spent in the pupal chamber varies from one day to 

 two weeks (Davis '03) . In my specimens the first larva pupated 

 on June 5, twelve days after the formation of the pupal chamber. 

 The remainder pupated at various intervals up to the 12th or 

 13th of June. Specimens were taken at various intervals, from the 

 time the pupal chambers were formed until the emergence of 

 the adults. They were killed with chloroform and the alimentary 

 canal removed under normal salt solution. Various fixing agents 

 were used, all with good results. 



Shortly after the formation of their burrows the larvae become 

 sluggish. The changes in the intestine which may be observed by 

 simple dissection are worthy of mention. At first the greater part 

 of the fore-gut is filled with a dense, blackish fluid, evidently 

 undigested food material, as this condition is found in the larvae , 

 while feeding and growing. Very early the fore-gut becomes 

 emptied and remains empty throughout the entire prepupal and 

 pupal period except at the posterior end where some of the con- 

 gested material, formed by the breaking down of the epithelium 

 of the mid-gut is found. Figure 11 shows the condition of the 

 fore- and mid-guts at the time of pupation. In this case the intima 

 of the gizzard was not shed at the time of the molt, the only 

 example of this found. It remained lodged at the anterior end of 

 the oesophagus. 



The histological changes undergone by the various systems of 

 organs during metamorphosis have not been fully investigated 

 except in a few scatterred species of insects. Even here the 

 changes observed are so complex that nearly every worker has' 

 offered a different interpretation of the phenomena. Owing to 

 this wide divergence in the interpretation of the histological 

 changes it will first be necessary to give a hasty review of the work 

 already done before taking up in detail my observations on Cory- 

 dalis. In this review I shall confine myself to the work that has 

 been done on the fore-gut. 



