596 ROBERT MATHESON 



rior part, with but slight changes in its nuclear and cytoplasmic 

 contents, becomes that of the imago. Deegener states that the 

 intima, both pupal and imaginal, is formed by a direct transfor- 

 mation of the inner plasma layer of the epithelium. 



Verson ('05) presents the detailed results of his work on Bom- 

 byx mori. In respect to the fore-gut he affirms the conclusions 

 given in his previous paper (1898). 



Thompson ('05) finds that in Culex the oesophageal epithelium 

 undergoes no metamorphosis. It is handed over intact' to the 

 imago with only an increase in the number of its component cells. 



Van Leeuwen ('07) in his studies on Isosoma graminicola finds 

 no imaginal ring present, though he states that the posterior part 

 consists of cells, differing from the rest and containing many 

 small nuclei. It is here that the most important changes during 

 metamorphosis occur. There is a marked lengthening of the 

 caudal part of the fore-gut during the pupal period by mitotic 

 cell division. The anterior division degenerates in situ and is 

 replaced by a hypodermal invagination. In the caudal region are 

 developed the sucking stomach and gizzard. 



Lubben ('07) finds but slight changes in the fore-gut of Trichop- 

 tera during metamorphosis. There is no imaginal ring present 

 (in the sense of Kowalevsky) though the entire oesophageal valve 

 might be considered one, as he states Deegener ('04) does for 

 the beetle intestine. In this portion there is considerable cell 

 increase. The main changes are the flattening of the pupal 

 epithelium, a considerable increase in length and the formation 

 of the characteristic imaginal gizzard. He doubts whether the 

 intestine functions in the adult. 



Russ ('08) in his studies on Anabolia laevis, one of the Trichop- 

 tera, finds a well marked imaginal ring present, which consists of 

 tall, cylindrical cells heaped upon one another in several layers. 

 The anterior part of the oesophagus, except for slight changes, 

 becomes that of the imago. Except in the very mouth region he 

 finds in this part a partial renovation through the divisions of the 

 larval cells. In the caudal portion the larval epithelium degen- 

 erates, being absorbed and replaced by the actively growing 

 embryonic cells. The pupal epithelium of the entire fore-gut 



