332 THE DEVELOPMENT OF THE NYMPH. 



existed. B}- opening the pupa on the third day, or even after 

 the legs of the nymph reach the middle or posterior third 

 of the abdomen, it is easy to remove the whole alimentary 

 canal, and it will be seen that the hind-gut is scarcely changed 

 in length, and is almost exactly as it was in the resting larva, 

 whilst the Malpighian tubules, increased in thickness and paler 

 in colour, still exist, although their cells are much vacuolated 

 and eroded. At this period it will be found that the intestinal 

 coil formed by the metenteron and the Malpighian tubes lie in 

 a cavity, bounded dorsally by the remains of the fat bodies of 

 the larva and ventrally by the chyle stomach, which is strongly 

 curved, its ventral surface convex and its dorsal surface concave 

 (PI. XIX.). 



In sections (PI. XVIII., Fig. 2) it will be seen that the chyle 

 stomach is covered by a layer of parablast cells on its ventral 

 surface, and that these cells connect it with the remaining lobe 

 of the fat body and surround the whole intestinal coil, between 

 the origin of the Malpighian tubules and the posterior three or 

 four millimetres of the gut. The cavity bounded by these 

 parablast cells also contains a quantity of coagulated fluid. 



On the fourth day these changes are complete, and the chyle 

 stomach is found to be split open on its dorsal aspect, so that 

 its cavity is continuous with the provisional cavity in which the 

 hind-gut and Malpighian tubes lie (compare PL VIII., Fig. 2, and 

 PI. XIX.). The cylindrical tube of new imaginal epithelium 

 becomes thinner and thinner on the dorsal aspect of the chyle 

 stomach, until at length it forms a crescent in section. The 

 ends of this crescent grow upwards over the wall of the pro- 

 visional cavity, and enclose the whole hind-gut and the remains 

 of the Malpighian tubes, which form the so-called corpus 

 luteum. 



The posterior part of the metenteron at the same time 

 becomes converted into an impervious cord of parablast, which 

 connects the temporary mesenteron with the posterior extremit\- 

 of the nymph. This cord is eventually contracted ; thus it acts 

 as a kind of gubernaculum, by which the new proctodaeal 

 rectum, formed by an invagination of the posterior segment of 



