FORE-GUT OF CORYDALIS CORNUTUS L. 593 



blow-fly (Musca vomitoria) he found an imaginal ring situated 

 at the point of union of the fore- and mid-gut epithehum. This 

 peculiar ring of cells was present in the youngest larva examined. 

 During metamorphosis the fore-gut becomes shortened and the 

 larval epithelium is replaced by the active proliferation of the 

 cells forming the imaginal ring. These proliferating cells form 

 the entire imaginal epithelium except the most cephalic part 

 which he considered as consisting of transformed larval epithe- 

 lium. The cast-off larval epithelium is destroyed by phagocytes. 



Van Rees ('89) in studying the same insect as Kowalevsky, 

 comes to essentially the same conclusions and verified in a remark- 

 able way the results of the Russian naturalist. 



Rengel ('96) in his studies on Tenebrio mohtor dismisses the 

 fore-gut with the statement that it retains its relative length and 

 shape through the life of the insect. 



Mobuscz ('97) comes to the conclusion that not only the mid- 

 gut but also the fore- and hind-guts undergo deep-seated changes 

 during the larval molts and at pupation. 



Karawaiew ('98) finds no imaginal ring present in the fore- 

 gut of Lasius flavus. During pupation the lumen of the caudal 

 portion of the fore-gut becomes greatly reduced. The epithelium, 

 which near the middle of the oesophagus consists of a single layer 

 of cells, becomes several layers thick at the caudal portion. He 

 was unable to explain this condition. From this region the crop 

 and gizzard develop through growth and differentiation. In 

 general he found but slight changes in the epithelium except at 

 the caudal end where the transformations are not fully explained. 



Vesron ('98) as the result of his studies on the metamorphosis 

 of the silk-worm adopts a new interpretation of the function of 

 the imaginal ring. He regards it simply as a center of growth 

 throughout the life of the insect. It originates in the ectoderm 

 from the germinal band and forms the point of invagination of 

 the stomodeum. During the larval life this imaginal ring pro- 

 liferates at each successive molt, thereby increasing the intestinal 

 epithelium. At the time of pupation it again proliferates in 

 exactly the same way as at the larval molts. The cells thus arising 

 from the imaginal ring unite with those previously formed, with- 



