362 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
For this reason, they stand in sharp contrast with the nearby metamor- 
phosing muscles. No other evidence of degeneration manifests itself 
until the pupal stage is reached. Then there begins a gradual atrophy 
of the muscles, during which the substance of the muscle becomes some- 
what broken, as is shown in Figure 39 (Plate 7). This figure, drawn 
from a cross section, is of muscles ¢, 7 (Plate 1, Figure 2), and Figure 
37 (Plate 7) is a longitudinal section of one of the similar group of 
mesothoracic muscles, both taken from pupae a few days old. The size 
of the area of cross section has diminished nearly one half at this stage ; 
this, however, does not mean a proportional shrinkage in volume, because 
the length of the fibres increases at pupation. Cross sections at this 
stage show Cohnheim’s areas, but only where viewed with a higher 
magnification than that used in making Figure 39. Longitudinal sec- 
tions (Figure 37) show fibrillation distinctly and cross striation faintly. 
The nuclei are apparently unchanged, retaining the nucleoli found in the 
nuclei of the larval muscles. In longitudinal sections they commonly 
project from the surface of the fibres, as shown in the figure. Sarco- 
lemma can usually be distinguished even at this stage. Tracheal cells 
are sometimes found in the fissures of the muscle substance (Figure 
39, cl.tr.), though this is not common. There can be little question 
of the identity of these cells with the tracheal cells of the remainder of 
the body, or of the fact that they are not leucocytes. There is no 
evidence of phagocytosis at any stage. 
From this period of the young pupa, until the old pupa, there is a 
gradual atrophy of the muscle substance of each fibre, until only a 
slender strand is left. This strand has in connection with it all the 
nuclei of the original fibre, these nuclei showing little evidence of de- 
generation until practically all of the remainder of the fibre has entered 
into solution. They then undergo a typical chromatolysis, as shown in 
Figure 38, nJ. Inside the nuclear membrane, the chromatin grains col- 
lect into masses of various sizes which at first stain deeply. These 
masses seem to persist for a short time after the dissolution of the 
nuclear membrane, for there may be found such chromatin masses (chr.) 
around which no nuclear membrane can be distinguished. No trace of 
these muscles can be found in pupae shortly before the emergence of the 
imago. The possibility that leucocytes may engulf some of these degen- 
erating nuclei ought to be mentioned. Such an engalfment of loose 
débris would agree with the well-known habits of leucocytes, and it might 
be contended that such appearances as are represented in Figures 41, 
44, and 45 (Plate 7) are due to this cause. No direct evidence can be 
. 
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