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 /a 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 sarcolerama 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. INIy observations are in almost 

 exact accord with those of Eengel ('96), so far as he has described the 



