508 



On the fourth day of larval life the foregut and rectum 

 degenerate and are rapidly regenerated by cells growing from 

 the imagina^l rings. The oesophagus is also partly regenerated 

 from the head integument, which creeps in through the mouth. 

 Tlie cells of the midgut disintegrate by a remarkable process 

 of globular degeneration and fall into the lumen of the gut ; 

 the epithelium is rapidly regenerated by the "imaginal" 

 cells of the midgut. The hepatic caeca become bodily drawn 

 in through the walls of the degenerating larval midgut. This 

 is produced by pressure from the regenerating epithelium. 

 The function of this epitiielium is to absorb the disintegrated 

 cells. The anterior portion of the epithelium then itself 

 breaks up into a fine debris and is absorbed by leucocyt-es; 

 the posterior part remains as the stomach. Meanwhile the 

 imaginal ring of the oesophagus has formed a great cone of 

 cells, which temporarily has closed the midgut in front. The 

 cells of this cone now grow back through the thorax and fuse 

 with the stomach; they differentiate to form gizzard and crop. 

 The malpighian tubes grow out from the anterior part of the 

 hindgut in the defaecating larva. The hindgut bends upon 

 itself on account of rapid cell proliferation ; the anterior part 

 is the small intestine, the hinder the short rounded rectum. 

 Within its walls is formed a pair of rectal glands, by thicken- 

 ing of the epithelium. 



The salivary glands, after disintegrating, are pliago- 

 cytised. A single salivary gland is formed by ingrowth of 

 cells from the regenerated oesophageal epithelium. Only one 

 salivary gland occurs in the imago. 



F . The Ductless Glands. 



(1) The Oen-ocytes. — The larval oenocytes grow in size 

 but do not proliferate; at metamorphosis they simply dis- 

 integrate. Leucocytes may at times aid in their removal. Tlie 

 imaginal oenocytes are formed from small clusters of cells 

 which grew inwards from^ the ectoderm in the early larva. 

 They separate and scatter themselves between the fat cells. 



(2) The Lateral Intestinal Glands are a pair of long 

 chains of glandular cells lying just beneath their lateral 

 hepatic caeca. Tliey disintegrate during metamorphosis. 



(3) The Dorsal A hdominal Glands. — The imaginal anlage 

 of these is a band of cells lying in the young larva dorsally 

 on tPie end of the midgut. They grow and proliferate late 

 in larval life and resemble empty fat ceils. During late pupal 

 life they assume a glandular appearance. They persist through- 

 out imaginal life and are not pericardial cells or young fat 

 cells. 



