592 EGBERT MATHESON 



The epithelium of the fore-gut 



Weismann ('64), the pioneer worker on the post-embryonic 

 development of insects, thought that the entire fore-gut in the 

 Muscidae was broken down during metamorphosis by a sort of 

 fatty degeneration, the degenerated epithehum falling into the 

 lumen of the intestine and forming the yellow body. Weismann 

 did not solve the method of regeneration of the fore-gut, though 

 he thought the entire intestine developed from the cellular mass 

 formed by the broken down larval tissues. This, he believed, 

 took place by a sort of free-cell formation; the particles isolating 

 themselves, forming enveloping membranes, losing their fatty 

 granulations, and each acquiring a nucleus. To these formations 

 Weismann gave the name of 'Kornchenkiigeln.' From such 

 cells the imaginal intestine developed. Later Kowalevsky ('87) 

 showed that the 'Kornchenkiigeln' are only phagocytic leucocytes 

 which have been swollen by the engulfment of large quantities 

 of larval tissues and they take no part in the formation of the 

 imaginal tissues. 



In Corethra according to Weismann ('66), the digestive epithe- 

 lium passes directly over to the imago without undergoing any 

 important modifications. 



Ganin ('76) states that: 



The fore-gut of the larva together with all its appendages are com- 

 pletely broken down (Anthomyia, Musca, Seatophaga, Eristalis, Stra- 

 tiomyia, Formica, Myrmica, Lithocolletis, Chrysomela, and Tenebrio). 

 The food for the formation of the imaginal epithelium is furnished by 

 the broken down larval cells. The products of the broken down epithe- 

 lium float freely in a thick fluid between the intima and the basement 

 membrane. If we observe closely the histological structure of the fore- 

 gut (at the end of the so-called proventriculus — oesophageal valve) we 

 find in each mature larva, at the point where the mid-gut epithelium 

 ends, a narrow strip of peculiar tissue which is sharply differentiated 

 from the rest. This narrow strip consists of very small, round, trans- 

 parent cells which possess all the characteristics of young, embryonic 

 tissues. The later developmental stages demonstrate that from this 

 small group of cells is built up the entire imaginal epithelium although I 

 was not able to trace the re-formation to the mouth. 



Kowalevsky ('87) is the first worker to give a complete and 

 detailed account of the metamorphosis of the fore-gut. In the 



