Apr. 5,1924 
Anatomy of the Apple Maggot 
17 
insect; but the fat cells of a mature honeybee larva stain rapidly in iodin 
and retain a rich, red-brown color after long washing in alcohol. This is the 
common test for glycogen. The same test gives weaker results on the fat body of a 
tent caterpillar (Malacosoma), and no reaction at all on that of the apple maggot. 
No one, however, has yet shown by chemical analysis of any fly larva whether it 
contains glycogen or not. 
The accumulation of proteid or albuminoid bodies in the fat cells was described 
by Berlese (4) for the blow-fly, and has now been noted by all subsequent observers, 
though the usual test has been that the bodies in question are colored by eosin 
and other protoplastic stains. The writer, however, applied the test with 
Millon’s fluid to the fat 
cells of the honeybee 
pupa and obtained the 
proteid reaction with 
characteristic pink color 
in the non-fatty inclu¬ 
sions of the cytoplasm. 
The fat body, then, is 
a very important organ 
in insects with complete 
metamorphosis, its func¬ 
tions being necessary to 
the proper reconstruc¬ 
tion of the imago, and 
we can readily under¬ 
stand why an insuffi¬ 
ciency of food or an 
improper diet during the 
larval period may result 
in a delay of the time of 
pupation, in the produc¬ 
tion of undersized adults, 
or in the death of the 
insect during its attempt 
at transformation. 
Some writers have 
noted, moreover, that, 
while metamorphosis is 
in progress, some of the 
fat cells appear to act as 
substitutes for the Mal¬ 
pighian tubules when the 
latter are undergoing re-, 
construction, for at this 
period, according to 
P&rez (39), some of them 
frequently contain crystals that later disappear. In the honeybee and other 
Hymenoptera, some of the cells of the fat body are apparently specialized as 
excretory organs, since they regularly contain small crystalline bodies in their 
cytoplasm. No such crystalline deposits were noted in any of the fat cells of 
Rhagoletis at any stage. 
Other cells, known as oenocytes, are usually found associated with the fat cells 
in insects, and are often regarded also as excretory in function. But the writer 
did not find such cells in the apple maggot, though they might show in histo- ’ 
88285—24f-2 
Fig. 6.—Fat cells of the larva and pupa. A, fat cells of half-grown larva 
of third instar, seen in optical section, the cytoplasm filled with oil 
droplets; 43-64 microns in diameter. B, a single cell of the same, more 
enlarged. C, surface view of fat cells of mature larva, showing oil 
globules crowded beneath surface film of granular protoplasm; 100-120 
microns in diameter. D, optical section of fat cells from larva con¬ 
tracting to puparium; 215 microns in longest diameter. E, optical 
section of fat cells just after formation of puparium, the cytoplasm 
now coarsely granular with proteid contents, oil less abundant. F, 
optical section of fat cells 48 hours after formation of puparium, the 
oil contents greatly reduced, the proteid granules increased in size 
and numbers; 135 microns in diameter. G, free spherical fat cells 
of fifth day (115 hours) filled with large proteid grains; 130-150 microns 
in diameter. H, surface view of fat cells at end of 14 days, proteid 
contents decreasing, fat increasing in globules that swell out at the sur¬ 
face; 150 microns in diameter. I, surface view of fat cell at end of 
18 days, cell full of fat globules bulging out on all sides, in small 
amount of finely granular cytoplasm; 172-215 microns in diameter 
