BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 341 
on Coleoptera will be spoken of first, and in greater detail than those on 
the other groups, as they are of more interest in connection with this 
paper. None of the researches on Coleoptera had, as a main object, the 
study of the muscular changes, and most of the investigators speak of 
them only incidentally. 
Coleoptera. The first paper in chronologcial order is that of Rengel 
(96), who describes the changes which occur in the midintestine of 
Tenebrio during metamorphosis, including a description of the changes 
of the intestinal muscles. The muscle layer of the larval intestine de- 
generates into a structureless protoplasmic zone in the late larva and 
early pupa. In this protoplasmic zone the individual muscle fibres can no 
longer be distinguished, though the nuclei of the larval fibres remain 
unaltered. No phagocytes (‘‘ Kérnchenkugeln” of Weismann, ’64) are 
present, this degeneration being entirely chemical. The intestinal mus- 
cles of the imago develop in this protoplasmic zone, but the exact 
method of their formation is somewhat in doubt. Apparently, part or 
all of the nuclei of the larval muscles remain and form the new muscles 
out of the material in which they are embedded. 
De Bruyne (97), speaking of phagocytosis in the development of in- 
vertebrates, treats of the changes in the hypodermal muscles of Tenebrio 
during metamorphosis. He finds a degeneration of the larval muscles, 
which begins with a chemical alteration of the muscle substance. The 
muscles soon break into fragments, which later are engulfed in leucocytes 
acting as phagocytes, thereby forming ‘‘ Kornchenkugeln.” These mus- 
cle fragments undergo fatty degeneration in the phagocytes, each becom- 
ing surrounded by a vacuole. The vacuoles with their contents fuse 
with one another until each phagocyte contains a few large vacuoles 
with correspondingly large fat globules inside. -These fat globules are 
then dispersed to the growing tissues, leaving the large vacuoles in the 
cytoplasm of the phagocyte. This is the beginning of degeneration for 
many of the phagocytes. 
Kriiger (98), describing the development of the wings in beetles 
(Tenebrio, Lema), states that he finds two larval muscles at the base of 
the wing (the flexor alae metathoracis, judging from his figures) which 
metamorphose into wing muscles of the imago. He concludes from this 
that the wing muscles of the adult are metamorphosed larval muscles. 
He also finds in the blood what he calls “ Weismannsche Kornchen- 
zellen.”’ 
In an article on the anatomy and metamorphosis of the intestinal 
canal of Anobium, Karawaiew (’99) states that there is no phagocytosis 
