BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 343 
After the classical researches of Weismann (’62, ’64, 66), the more 
important of the earlier authors are Kiinckel d’Herculais (’72, 775), 
Ganin (76), and Viallanes (81, ’82). Later authors have shown that 
the results of these papers on the histological changes of the muscles 
during pupal life are not of great importance, so that they need not be 
mentioned in detail here. The higher (cyclorraphic) and the lower 
(orthorraphic) Diptera seem to present, together with other differences, 
two distinct types of muscle degeneration, and so the papers on each 
group are here reviewed separately. 
a. Cyclorrapha. Van Rees (’84, ’88) and Kowalevsky (’85, ’87) both 
find in Calliphora that the larval muscles undergo phagocytosis. The 
leucocytes penetrate the muscle fibres, which they break up into frag- 
ments; these, together with the muscle nuclei, are engulfed by the 
leucocytes and digested. The leucocytes with their inclusions are the 
“ Kérnchenkugeln” of Weismann (64). Van Rees finds that three 
pairs of muscles in the dorsal part of the mesothorax are exempt from 
this fate, and that they metamorphose to form the indirect wing muscles 
of the adult. 
Lowne (90-95) confirms the two preceding authors in regard to the 
phagocytosis of the larval muscles, but denies the metamorphosis of the 
three pairs of muscles of the mesothorax described by Van Rees. He 
states that all of the imaginal muscles are newly formed in the pupa, 
being produced from mesoderm cells which are derived from the imaginal 
disks. 
De Bruyne (’97) practically agrees with Van Rees and Kowalevsky, 
except that he finds that the leucocytes are not the active agents in 
breaking up the muscle substance into fragments, the muscle being 
frequently broken up before the arrival of the leucocytes. He also finds 
that some of the nuclei of the larval muscles are not immediately de- 
stroyed. These, collecting a portion of the sarcoplasm of the fibre about 
themselves, act as myoblastic phagocytes, engulfing and digesting the 
muscle fragments. He calls this “ autophagocytosis,” to distinguish it 
from ordinary or leucocytic phagocytosis. 
The results of the studies of Noetzel (’98) accord with those of De 
Bruyne in regard to the breaking up of the muscle before the arrival of 
the leucocytes. 
Berlese (99, :00, :00%, :01, :02, :02°) differs from the above authors in 
many essential points. He states that there is no phagocytosis, the 
ingestion of the sarcolytes and muscle nuclei by the leucocytes being for 
the purpose of distributing those elements to all parts of the body. The 
