459 



have greatly diminished in size; they still contain a few 

 grains and fat globules (fig. 96), but while in the adult larval 

 fat cells these reserve products give the cells their charac- 

 teristic appearance, the cytoplasm merely acting as a supporting 

 tissue for them, in the late pupal period these conditions are 

 reversed. The faintly granular cytoplasm now predominates, 

 and only scattered grains and fat globules remain. The fat 

 cells, however, now no longer resemble those of the first instar 

 before the reserve materials accumulated. They float as 

 irregular shapeless masses within the cavity of the head, and 

 although a few survive the pupal period, most have degener- 

 ated before then; their reserve substances have all passed 

 back into the blood from which they originally came, and the 

 brain and the great eyes have doubtless grown at their 

 expense. 



These degenerate shapeless cells are finally, in the four-"^ 

 day pupa, removed by the leucocytes (fig. 97) ; not before this 

 time, however, does any phagocytosis occur. "" """ "^ 



In the thoracic region the fat-body undergoes similar 

 degeneration, and though a, few fat cells in the ventral portion 

 of the thorax persist, even throughout imaginal life, yet the 

 greater number disappear entirely during the fourth day of 

 pupal life ; at the expense of their reserve substances the great 

 wing-moving musculatures have developed. 



In the newly formed pupa the thoracic region contains 

 numerous fat cells (fig. 154), but as the longitudinal muscles 

 grow they begin to push these aside. Tliose cells which have 

 been so unfortunate as to become entangled amongst the 

 growing muscles become stretched into elongated masses, very 

 well seen in the thirty-six hour pupa; the others retain their 

 usual shape. But the result is always the same; the cells 

 gradually give up their reserve products (fig. 98), and like 

 the fat cells of the head, remain as irregular hulks, whether 

 compact or branched, or greatly elongated and compressed . 

 between the thoracic muscles. Here in t he fourth -day pupa j 

 they are fallen upon by the leucocytes and soon are no longer / 

 seen. 



Similar degeneration may be observed in those fat cells 

 which were forced into the cavities of the appendages. 



In the abdomen the degeneration during pupal life is 

 much less complete; indeed, although occasional leucocytes 

 may be observed lying amongst the cells of the fat-body as 

 late as the fourth-day pupa, yet these seem to have no effect 

 upon the fat cells. TTie latter remain practically at a constant 

 size; the fat globules which they contain may diminish in 

 \ number, but do not disappear. The grains, however, dis- 

 appear to a large degree; the large grains are far less 



