509 



Q. The Fat-hody. 



The cells of the fat-body do not proliferate during larval 

 life. They grow in size and store fat and other (protein ?) 

 foodstuffs in their cytoplasmic meshwork. Before defaecation 

 excretory crystals may accumulate within them, though these 

 soon disappear when the malpighian tubes form, and are cast 

 into the stomach, where they accumulate during the pupal 

 period. 



Tlie storage products gradually disappear during pupa- 

 tion, as the imaginal tissues grow at their expense. Fre- 

 quently the remnants of the fat cells, deprived of their storage 

 substances, are phagocytised. Others persist throughout pupal 

 and imaginal life. There is no regeneration of fat-body. 

 Some of the fat cells are seen to have a capacity for limited 

 phagocytosis. 



H. The Gonach. 



These occur in the youngest larvae as a pair of club- 

 shaped masses attached to the ventral body wall. They 

 begin to grow at metamorphosis and develop directly into the 

 adult organs. The male organs often show ripe sperms 

 already in the third day of pupal life. The ovaries continue 

 to develop during imaginal life. 



/. The XervGus System. 



In the larva there is a brain above the oesophagus con- 

 nected to a ventral nerve cord consisting of tM^elve ganglia, 

 the last of which consists of three fused ganglia. A single 

 stomotogastric ganglion is present. The nerve cord and brain 

 are composed of larval cells and imaginal neuroblasts. Dur- 

 ing metamorphosis the former degenerate, and the latter 

 proliferate. In the nerve cord the dead cells which form 

 masses of necrotic tissue there, are quickly absorbed; into 

 the degenerate strands of fibres that run along the cord, the 

 new nerve cells send their growing nerve fibres, and no dis- 

 oontinuity is to be observed. In the peripheral nerves, the 

 fibres break into globules which, passing out, dissolve in the 

 blood or are phagocytised. All these changes take place 

 within the splanchnopleural covering of the nerve cord, w^hich 

 itself metamorphoses by imaginal cells replacing dead larval 

 cells, and no discontinuity occurs in it. It follows, therefore, 

 that no' discontinuity is to be observed in the nerve cord and 

 peripheral nerves as a whole, although the most profound 

 ■changes are taking place within it. These changes are com- 

 pleted before pupation; a migration of nerve cells (i.e., of 

 ganglia) then commences and the concentrated nervous system 

 of the imao-o is formed. 



