418 



Their transformation during metamorphosis has been studied 

 more frequently than that of any other organ ; nevertheless 

 our knowledge of the process, in spite even of the recent 

 work of Perez, is far from correct. Even the name "wingf 

 muscles," by which they are generally known, is inaccurate; 

 though their function is to move the wings, they usually 

 have no direct attachment to these. Most of the observa- 

 tions have been made on the blow-j9.y, Calliphora, and it is 

 therefore possible to compare the observations of the various 

 authors. 



Kowalevsky (1885) regarded the larval thoracic muscles 

 as undergoing phagocytic destruction along with the other 

 specialized larval organs; the imaginal muscles, he regarded 

 as being rebuilt from a number of mesenchyme cells, lying 

 free within the body cavity. 



Van Rees (1889) observed that three of the longitudinal 

 thoracic muscles did not disappear; on the contrary, their 

 nuclei, he believed, underwent multiplication, while the 

 mjiscle itself appeared to possess a resistance against leuco- 

 cytes. The newly formed nuclei became spherical, and 

 migrating into the muscle substance, transformed this into 

 the muscle as it occurs in the adult. 



Korotneff (1892), working with a moth (Tinea) con- 

 cluded that the mesenchyme cells found by Kowalevsky were 

 superfluous structures in that insect. He could find no trace 

 of them in the moth, and believed he could confirm Van Rees' 

 observation on the rejuvenescence of muscle nuclei. The con- 

 tractile part of the muscle fibres, as a result of constant 

 functioning during larval life, became exhausted, and under- 

 went granular degeneration, forming long plasmatic columns 

 C'Plasmastrang"). The rejuvenated nuclei penetrated into 

 the mass and formed a separate nuclear column (''Kern- 

 strang"). Tbese gradually reorganized the disintegrated 

 myoplasm, and eventually formed the adult muscles. Leuco- 

 cytes took no part in the transformation. 



Perez (1910) re-examined the metamorphosis of the 

 thoracic muscles of Calli'phora ; while confirming the observa- 

 tions of Van Rees and of Korotnelf that certain larval thoracic 

 muscles did not disappear, he attributed to these quite an 

 insignificant function in the rebuilding of the adult thoracic 

 muscles. He regarded them merely as the "scaffolding" on 

 which the imaginal muscles arranged themselves. To the 

 "rejuvenated nuclei" of Van Rees and Korotneff he 

 attributed quite a different origin. They were the mesenchyme 

 cells of Kowalevsky, and bore no relation whatever to the 

 larval nuclei. These myoblasts, as he now called them. 





