446 



The cells in the mid-region of the hindgut are, in the 

 early pupa, in a state of rapid proliferation ; and this, con- 

 tinuing into the next day, produces a considerable bending of 

 the anterior region. That portion behind the centre of pro- 

 liferation is the rectum; the portion anterior to it, the small 

 intestine. The amount of this proliferation seems to vary 

 considerably, so that, while the intestine is sometimes quite 

 bent upon itself, at other times the bending is far less marked. 



Having arrived at its maximum size, the cells of the 

 small intestine begin to differentiate; but the differentiation 

 never becomes very marked, and the epithelium remains as 

 a single layer of elongated loosely arranged cells, on whose 

 surface an equally irregular chitin sheath is secreted. The 

 organ is evidently capable of considerable stretching. 



r-^ Already in the fresh pupa the rectal region of the hind- 

 \ gut is distinguishable from the small intestine by the "spindle 

 1 shape" of its epithelial cells. The tube is already more dis- 

 tended than the anterior portion, but six hours later attains 

 r^its adult proportions. It is not till six to eight hours after 

 pupation that the larval muscles j&nally disappear by phago- 

 ] ,cytosis, after having undergone globular degeneration. 

 The adult muscles develop in the usual manner. 



The Rectal Glands. 



During the last hours of larval life the cells of the 

 anterior region of the rectal portion of the hindgut begin to 

 proliferate and grow in the -form of two small clumps of 

 elongated cells into the cavity of the enlarging rectum (fig. 

 161). These are the rudiments of the single pair of rectal 

 glands, and have already attained to a considerable size in 

 the fresh pupa. 



The rectal glands grow considerably in size. The elongated 

 cells dispose themselves in a single layer with their long axes 

 vertical to the surface of the gland; the whole structure has, 

 in the eight-hour pupa, a short cylindrical shape. It is solid 

 except below, where there is a cavity lying loosely in which 

 is a large number of much smaller cells. They are the 

 elongated filamentous cells already described. A cuticle is in 

 process of secretion. The rectal gland lies in close contact 

 with the wall of the rectum from which it has been developed, 

 and there appears to be no communication through it, 

 between the cavity of the rectal gland and the haemocoele. 



During the rest of the first day the rectal gland elongates 

 considerably, by growth of its cells, not by their proliferation. 

 The small basal cells now dispose themselves in a ring at the 

 base of the gland; in the twenty-one hour pupa some have 



