444 



form the cavity of the gizzard and ''drum-shaped" chamber. 

 The more anterior part is more widely dilated. Here the 

 crop will develop. 



The development of the crop is very curious. The epi- 

 thelial cells entirely lose their columnar character; they 

 flatten out more and more, and in the pupa one day old have 

 become highly wrinkled. The flattening continues, and 

 instead of a small conical chamber with very thick walls 

 there is formed a highly distensible collapsed bag with very 

 thin paper-like walls (fig. 156). The cell differentiation 

 closely resembles that observed in the cells of the differ- 

 entiating wing epithelium. 



The gizzard rapidly differentiates. Already at the end 

 of the first day its lumen has become triradiate; this is 

 brought about by the epithelium arranging itself in the form 

 of three short longitudinal plates, bent along their longi- 

 tudinal midline. The epithelial cells are still embryonic in 

 appearance. The myoblasts have already arranged them- 

 selves in their definite positions. Their future development is 

 exactly the same as occurs in the case of other muscles and 

 need be referred to no more. 



In the thirty-six hour pupa the three bent epithelial plates 

 are beginning to secrete chitin on their inner walls; and the 

 posterior portion, where chitinisation does not occur j^ is 

 observed to be marked off as a small rounded chamber, into 

 which a short ''filament" projects from the hinder wall 

 (fig. 156). 



During the next day the chitinisation strengthens, and 

 with the appearance of the muscle striations the gizzard attains 

 its adult proportions. 



Cell proliferation of the drum-shaped chamber occurs 

 also at this time, and at last a communication between foregut 

 and stomach is established (fig. 157). 



(C) The Metamorphosis of the Hindgut. 



Tlie walls of the rectum undergo the same changes during 

 larval life as occur elsewhere in the larva, i.e., there is a 

 growth in cell size, in the absence of cell division ; the muscle 

 fibres during the second instar gradually acquire striation. 



But about half a day after feeding ceases, the cells of the 

 anterior end of the rectum, which constitute the imaginal disc, 

 become active, and proliferating greatly at last bring about a 

 junction of the cavities of the midgut and hindgut. The actual 

 opening is large and funnel-shaped. Not till this time, there- 

 fore, does the embryonic proctodaeal invagination open into 



