BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 345 
Hymenoptera. 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, 799%, :00, :01, :01*, :02) and Pérez (’99, :00) dispute 
the observations of the two authors last cited, stating that there is an 
invasion of the larval muscles by leucocytes. Pérez 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 ‘‘ Kérnchenkugeln ” formed, 
a statemeut 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 
sphincter, 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 the 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 Pérez. 
According to Berlese, the imaginal myoblasts of Karawaiew are the same 
as his “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 
