362 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



For this reason, they stand in sharp contrast with the nearhy 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 ^, -q (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, d. 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, nl. 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 

 debris 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 



