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The Destruction of the Larval Musculature. 



Like the other highly specialized larval organs, the larval 

 musculature undergoes total destruction at the end of larval 

 life. 



The muscles of the larva do not, however, all disappear 

 simultaneously. The pharyngeal dilators disappear first, at 

 about the time of larval defaecation. Certain thoracic muscles 

 begin to disintegrat/e several hours later. The abdominal 

 muscles persist till a few hours after pupation. 



(1) The Dilators of the Pharynx. 



The disappearance of these muscles is closely associated 

 with the development of the pharyngeal muscles of the imago, 

 and will be more conveniently described there. 



(2) Tlie disintegration of the upper three pairs of thoracic 

 muscles and of the oblique thoracic muscles is closely con- 

 nected with the development of the great vertical and longi- 

 tudinal thoracic muscles, and will be considered in connection 

 with these. The other thoracic muscles disappear early in 

 larval life. I have not, however, carefully examined their 

 process of destruction. It is improbable that this should be 

 unlike the process as we see it in certain abdominal muscles, 

 which I shall here describe carefully. 



(3) The Muscles of the Abdomen. 



Many of the longitudinal muscles of the abdomen of the 

 larva are disintegrated by the action of the embryonic cells 

 of developing imaginal muscles. The description of these will 

 be deferred till the regeneration of the muscular system is 

 considered. 



On account of the marked differences shown by the ver- 

 tical (oblique) and longitudinal abdominal muscles in their 

 mode of disintegration, it will be best to consider them 

 separately. 



(a) The Longitudinal Muscles. 



It is mainly in the ventral portion of the abdomen that 

 disappearance of the longitudinal muscles independent of the 

 action of developing myoblasts occurs. 



Though the process first becomes marked in freshly formed 

 pupae, yet, for a considerable time previous to this, the 

 muscles have been undergoing a process of internal degen- 

 eration . 



In the larvae at about the time of defaecation the nuclei 

 begins to appear abnormal ; . they have developed great 

 nucleoli, much larger than those usually occurring in nuclei, 

 which may be, at this stage, crowded with numerous minute 

 highly refractile crystals. Most of the muscles, however, 



