C 



443 i 



extensive-destruction of Jfhem^^^ occurs. The process com- 

 mences shortly after pupation, but is quit^e different from what 

 occurred in the larval midgut. The whole epithelium of the 

 anterior half of the midgut begins to break up into a mass 

 of rough granules. The muscle fibres of the intestine, losing 

 their striations, join in the general process of disintegration, 

 and^~what was af^w hours earlier an actively functioning 

 tissue, is now a loose accumulation of granular debris. This 

 time, however, the leucocytes act, and swarming into the 

 disintegrated mass rapidly absorb it (fig. lboJ\; after six hours 

 not a trace of the temporary midgut remains. The small 

 conical projection of the foregut takes part in the general 

 destruction, and nothing of the renovated midgut remains 

 except the posterior half, in which no disintegration whatever 

 has occurred. This portion remains with but little change u-jTi^. ^ 

 as the stomach of the adult insect. Its structure has been vC^) 

 referred to already. .^% tux^ 



But before the anterior half of the midgut has had time ^^^Xi^^ 

 to disappear entirely, the cells of the inner layer of the great 

 conical circumoesophageal imaginal ring have sprung into 

 activity; they grow rapidly, moving evidently by amoeboid 

 action, along the pathway afforded by the disintegrating 

 mass, and, extending right through the thorax and anterior 

 abdominal segments, at last reach, in the eight-hour pupa, 

 the anterior end of the hinder half of the midgut which has 

 survived these violent scenes unchanged. From this newly 

 formed structure the post-oesophageal part of the foregut 

 soon begins to differentiate. 



In the thoracic and propodeal regions it is formed, and 

 persists,* as a very fine, almost capillarv, tube, 8/x to lOju, in 

 diameter (cf. fig. 156). The cells, which are at first irregular 

 and embryonic in appearance, soon elongate, grow spindle- 

 shaped, and dispose themselves longitudinally. They seem 

 to lose part of their cytoplasm later in pupal life, and in the 

 adult insect appear almost devoid oif it. 



But the abdominal portion of the foregut undergoes a 

 much more complex differentiation. In the eight-hours pupa 

 its posterior extremity is seen as a thick-walled, somewhat 

 conical and slightly dilated chamber (fig. 155). This will 

 develop into the crop, the gizzard, and the ''drum-shaped" 

 chamber. Its epithelium is composed of. long columnar cells, 

 which gradually merge, in the region of the petiole, into 

 those of the narrow capillary portion. Surrounding the 

 structure is already to be seen a number of cells forming a 

 distinct layer of myoblasts. The lumen does not yet com- 

 municate with that of the stomach, but ends blindly. The 

 hinder part of this lumen is rather constricted and will 



