358 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
duration in some muscles than others, and is not found in all of the 
muscles at the same instant. 
During the period of these destructive changes in the contractile 
muscle substance, the angular strands become more rounded and 
separated, precisely as in the wing muscles during the same period. 
However, the nuclei, with rare exceptions, remain at the periphery of 
the strands. The tracheal cells are never formed as numerously as is 
shown for the wing muscles in Figure 19, and, in fact, are fewer at all 
stages than in the wing muscles at the corresponding stages. 
The reconstructive changes begin in the pupa, at varying times for the 
different muscles, the same as has been shown concerning the beginning 
of the destructive changes. It is difficult to determine much about the 
reconstruction of the fibrillae of these muscles, because the fibrillae are 
so small. In fact, it is not certain that they have been recognized. In 
cross sections of these muscles from old pupae there appear irregular 
polygonal areas of small size (less than 1 yp in diameter), which, how- 
ever, are presumably Cohnheim’s areas, rather than the cross sections of 
separate fibrillae. These become more evident in later stages, and show 
plainly in the imaginal muscles (Figure 18). Longitudinal fibrillation 
appears at the same time that the polygonal areas begin to show, whereas 
cross striation is not seen until the day before the emergence of the. 
imago. A longitudinal section of a stage corresponding to that shown in 
Figure 18 is given in Figure 17. This presents the usual appearance of 
the cross-striated muscles of the legs of insects. 
y- Imaginal Period. The same muscle that is shown in cross section in 
its larval state in Figure 49 (Plate 7) is represented in its imaginal state 
in Figure 50. A comparison between the two figures will reveal how 
simple the changes between the two stages really are. In the imaginal 
muscle, there is evident a superficial layer of sarcoplasm with the nuclei 
embedded in it. A sarcolemma is present about each fibre, having been 
- formed during the late pupal stages. The tracheal cells have developed 
into tracheae, which, however, do not penetrate the muscle substance as 
in the case of the indirect wing muscles. Most of the muscles of the leg 
type increase somewhat in size during metamorphosis, but this increase 
is small compared with the growth of the majority of the wing muscles. 
(3) Metamorphosis of the Intestinal Muscles. 
The intestinal muscles undergo changes precisely similar to those 
described for the leg type of muscles. My observations are in almost 
exact accord with those of Rengel (’96), so far as he has described the 
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