breed: metamorphosis of the muscles of a beetle. 345 



Hymenojptera. The first, and one of the most important, of the re- 

 searches on Hymenoptera is that of Karawaiew ('97, '98,) on Lasius. 

 He finds that there are two kinds of nuclei in the muscle fibres of the 

 old larva, one larger than the other. During metamorphosis the larger 

 nuclei degenerate, while the small ones, which are imaginal myoblasts, 

 divide amitotically and after the fibrillar substance of the larval muscle 

 has been dissolved, form the imaginal muscles. The imaginal muscles 

 are, therefore, metamorphosed larval muscles, except in the case of the 

 appendicular muscles, which are of new formation in the pupa. 



Terre ('99, :00, :00*) confirms most of Karawaiew's results. He adds, 

 among other new observations, that the two kinds of nuclei are present 

 in the muscles of larvae which had but just escaped from the egg. 



Anglas ('99, '99*, :00, :01, :01% :02) and Perez ('99, :00) dispute 

 the observations of the two authors last cited, stating that there is an 

 invasion of the larval muscles by leucocytes. Perez speaks of this in- 

 vasion as the beginning of an active phagocytosis which destroys the 

 muscles. However, according to the statements of Anglas, the substance 

 of the muscles is digested by the secretions of the leucocytes without 

 any ingestion of solid particles. This is not true intracellular digestion 

 or phagocytosis, but, rather, an extracellular digestion, for which he pro- 

 poses the term " lyocytosis." There are no " Kornchenkugeln " formed, 

 a statement in which all of the authors concur. Anglas finds that this 

 lyocytosis totally destroys certain muscles (those of the pharynx, of the 

 anterior part of the thorax, of the posterior part of the abdomen, the rectal 

 spliincter, and the transverse muscles ) ; while in the thoracic and intes- 

 tinal muscles the nuclei of the larval muscles survive and give rise by 

 fragmentation to small nuclei. These in turn form the imaginal muscles 

 in the midst of the mass left from the destruction of tlie remainder of 

 the fibre. The abdominal muscles do not undergo so deep-seated a 

 metamorphosis, inasmuch as the leucocytes never invade their substance. 

 The imaginal muscles in this case likewise are derived from nuclei which 

 arise by the direct division of the larval nuclei. There are some muscles 

 of new formation in the pupa which are derived from indifferent mesoderm 

 cells. 



The results of Berlese's ( :01, :02'') observations agree more with 

 those of Karawaiew and Terre than with those of Anglas and Perez. 

 According to Berlese, the imaginal myoblasts of Karawaiew are the same 

 as bis " sarcocytes," and are derived from the larval muscle nuclei by 

 direct division. These may remain in the place where they are formed 

 and give rise to " myocytes," which then develop into the imaginal muscles 



