Apr. 5, 1924 
Anatomy of the Apple Maggot 
27 
All of these tissues are regenerated without destroying the continuity of the 
organs concerned. The pupa is never without a hypoderm, never without an 
alimentary canal (PL 6, B). The new cells advancing from the imaginal buds 
follow closely on those disappearing, or overlap them. The new forms of the or¬ 
gans result from the forces of heredity inherent in the new cells or somehow im¬ 
posed upon them. 
In the organs of mesodermal origin, however, especially in the muscles, the 
tissues are much more profoundly affected by the processes of metamorphosis; 
yet, even here, in the simpler forms of metamorphosis, the muscles are mostly 
remodelled in situ, and in the higher flies, where the general dissolution is most 
intense, some of the muscles are said to be modified only by the addition of new 
fibers. Most of the larval muscles in the Muscoidea, however, go into complete 
histolysis, while the new ones are built up with little relation to those of the larva. 
In the apple maggot the 
beginning of histolysis in 
a muscle is first evident in 
a few fibers that lose their 
cross striation and appear 
to melt together into a 
homogeneous granular 
mass. This mass then 
breaks up into small frag¬ 
ments, which are at first 
densely packed but which 
are soon dissociated by a 
clear substance that ap¬ 
pears among them as if 
formed from the liquefy¬ 
ing of some other parts of 
the muscle tissue, prob¬ 
ably the sarcoplasm. In 
this way the muscle disin¬ 
tegrates, resulting in the 
appearance of clear plas- 
mic areas along its edges 
and between its fibers, 
filled with granular frag¬ 
ments of the formerly 
striated tissue. As dis¬ 
solution progresses deeper 
and deeper into the body 
of the muscle, the plaslnic 
lacunae enlarge and engulf 
an ever-increasing number of the fragments. Finally, the lacunar plasma dissolves 
along its outer edges and the muscle fragments float off free into the blood. 
Among the bodies in the plasmic areas of a disintegrating muscle we may 
distinguish several sorts. The most numerous are simple, oval, granular pieces 
of the fiber substance, the sarcolytes of other writers. Then there are smaller 
bodies containing nuclei, virtually nucleated cells derived from the muscle tissue. 
These are the caryolytes of Berlese (4, 5) . Finally, there are often large numbers 
of free muscle nuclei, or nuclei surrounded by only a very small amount of clear 
protoplasm. Figure 8, A, shows a piece of a larval pharyngeal muscle in which 
histolysis is well advanced, and in which is seen the formation of the various 
elements of disintegration, first deep in the muscle tissue, then liberated into the 
Fig. 8.-—Histolysis of muscle tissue. A, piece of pharyngeal muscle in 
histolysis just after formation of puparium, showing disintegration 
of muscle into fragments or sarcolytes and the liberation of the latter 
at the dissolving edge. B, showing various elements given off from 
muscle in histolysis; a, free muscle fragments or sarcolytes; b, globules 
of fragments; c , free muscle nuclei; d, a muscle “cell” or muscle 
nucleus in a piece of muscle substance. C, a globule of sarcolytes, 
about 34 microns in diameter. D, free sarcolytes or muscle frag¬ 
ments, 25 to 30 microns in length. E, cell containing several small 
bodies, perhaps a free muscle nucleus after division into secondary 
nuclei, 8 to 10 microns in diameter. F, sarcolyte globule in early stage 
of disintegration. G, globules in more advanced stages of disintegra¬ 
tion. H, globules in last stages of breaking up into free sarcolytes 
