breed: metamorphosis of the muscles of a beetle. 359 



changes in the muscles of the intestine. I have studied especially the 

 region of the proventriculus, where the muscle layers are well developed. 

 No differences were discovered between the changes of the muscles of this 

 region and those of the remainder of the intestine. Two general figures 

 are given. Figure 51 (Plate 7) is a portion of the wall of the proventri- 

 culus in a larva about to pupate, and Figure 52 is a similar figure from 

 an old pupa. The muscle fibres are found in two layers : a circular layer 

 inside (mu. crc), and a longitudinal layer outside {mu. Ig.). Their 

 structure is similar to that of the other larval muscle fibres, except that 

 the nuclei are more frequently found at the centre of the fibres and that 

 Cohnheim's areas are arranged similarly to those shown in Figure 20 

 (Plate 6) ; this particular figure, however, is not from one of the larval 

 fibres. The principal difference between the destructive changes in these 

 muscles and in those of the leg type is, that they are still slower in 

 being completed than the latter. The larval fibres rarely, if ever, divide 

 lengthwise to form new fibres, those in the larva being apparently as 

 numerous as those in the imago. The tracheal cells are slower in mak- 

 ing their appearance, and only a few are found in this region at the time 

 of pupation (see Figure 51, which does not show any of them); whereas, 

 even before this time, they are numerous in the regions of the other 

 metamorphosing muscles. Compare Figure 14 (Plate 6) and Figure 49 

 (Plate 7), which are from younger pupae than Figure 51. The intestinal 

 muscles show cross striation much longer than any of the other metamor- 

 phosing muscles, as the striation does not disappear until the pupa has 

 undergone nearly half of its development. Longitudinal fibrillation dis- 

 appears almost as quickly, and thus a structureless stage, shown in 

 Figure 52 {mu. crc), is reached. 



During all the time in which the destruction of the contractile ele- 

 ments is taking place, the muscle nuclei show no apparent changes. 

 No cases of amitosis have been seen, though they are common in the 

 other metamorphosing muscles ; nor is there any evidence of degenera- 

 tion and phagocytosis such as Deegener (:00) states that he finds. It 

 seems as if Deegener's statement, that there is phagocytosis of these 

 muscles, such as Kowalevsky ('87) and Van Rees ('88) found in Mus- 

 cidae, must be strongly questioned. For, in the first place, both Rengel and 

 I have failed to find evidence of it in Coleoptera. Secondly, it is evident 

 on reading Deegener's paper that this statement is based more on infer- 

 ence than actual observation. No satisfactory figure nor description is 

 given of the phenomena which take place when the leucocytes attack 

 the muscles. Apparently the only ground for the statement is that be 



