FORE-GUT OF CORYDALIS CORNUTUS L. 595 



the larval epithelium is forced cephalad to become the imaginal 

 oesophagus. 



Vaney ('02), in his studies on dipterous larvae, finds imaginal 

 rings present in the following; — Chironomus, Anthomyia, Stra- 

 tiomyia, Tanypus and Gastrophilus. In Stratiomyia he also found 

 in front of the oesophagus a small buccal disc, while in Gastro- 

 philus there is one just caudad of the pharynx. Only in Gastro- 

 philus did he study the metamorphosis of the fore-gut. There 

 was deg'eneration of the larval epithelium in situ and its destruc- 

 tion by phagocytes. The imaginal epithelium arises exclusively 

 from the imaginal ring and the post-buccal disc. 



Deegener ('04), in his studies on the metamorphosis of Cybister 

 roeselii, records a prominent imaginal ring situated at the point of 

 union of the fore- and mid-gut epithelium. He divides the meta- 

 morphosis into two distinct periods; — (1) the shedding of the 

 larval intima and the formation of the pupal epithelium; (2) the 

 molting of the pupal intima and the rebuilding of the imaginal 

 epithelium. The first period is completed about twenty-four 

 hours after pupation. The epithelium of the anterior portion of 

 the oesophagus becomes that of the pupa, with but shght changes 

 in the nuclear chromatin and cellular cytoplasm. The epithe- 

 lium of the posterior portion breaks down and is forced into the 

 lumen by the rapid forward growth of the imaginal ring. The 

 degenerated larval cells form a deeply staining mass lying between 

 the molted larval intima and the developing pupal epithelium. 

 The imaginal ring cells divide mitotically with extreme rapidity. 

 The spindles are always located in the plasma layer next the 

 lumen, their long axes parallel to that of the intestine. Numerous 

 degenerating nuclei are observed directly in front of the imaginal 

 ring. Deegener thinks that the larval cells fail in the struggle with 

 the imaginal, become broken down and absorbed by the more 

 actively growing embryonic cells. . 



The pupal epithelium is completed about the end of the third 

 day after pupation. Then immediately begins the formation of 

 the definitive fore-gut. The posterior part, through growth and 

 a great increase by the division of the imaginal ring cells, becomes 

 differentiated into the crop and gizzard of the adult. The ante- 



