BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 361 
from the structureless muscle substance containing the larval nuclei is 
the same as the reconstruction of the leg muscles. That is, longitudinal 
fibrillation appears first, then cross striation, the latter appearing about 
the time of the emergence of the imago. At the same time Cohnheim’s 
areas become plainly distinguishable, and have the pattern shown in 
Figure 20 (Plate 6), which is drawn from the cross section of a single 
fibre of the foreintestine of the imago. The muscle substance, when 
structureless, stains deeply with thionin, but after the fibrillae are 
formed, it stains scarcely at all. The nuclei remain as they were, while 
a new sarcolemma is formed about each fibre in the old pupa. The 
tracheal cells of this region give rise to the new tracheae and possibly, 
as stated before, to imaginal leucocytes. 
Deegener, who speaks of these tracheal cells as spindle cells (page 146, 
et seg.), derives the intestinal musculature of the imago from them. He 
gives no conclusive proof of this derivation in any case, however. In 
the region of the midintestine he was unable to distinguish these 
spindle cells with certainty, so that his conclusion that the muscles of 
this region are formed from these cells is pure assumption. He is 
forced to make such an assumption by his conclusion, — which has 
already been shown to be incorrect, — that there is a phagocytosis and 
total destruction of the larval muscles. There is no reason for suppos- 
ing that these cells form the intestinal muscles of the imago any more 
than that they form the muscles of the remainder of the body, and this, 
as has been shown, is not true. 
c. HISTOLYSIS OF THE LARVAL MUSCLES. 
The muscles which undergo histolysis in the pupa present great indi- 
vidual variation as to the time when degeneration begins. There are 
also variations in the details of the degeneration, which are of such a 
nature that they form a partial transition to metamorphosing muscles. 
However, no instance of a muscle which sometimes degenerates and 
sometimes metamorphoses into a rudimentary imaginal muscle has been 
found, though it does not seem improbable that such may be present 
in some of the beetles. 
The group of muscles of the metathorax designated in Figure 1 (Plate 
1) by the Greek letters B, y, 5, «, & 7 belong to a class of degenerating 
muscles which are very distinct from the metamorphosing muscles. This 
group will serve as a type in describing the degeneration and the differ- 
ences between these and the other degenerating muscles noted later. 
The substance of these degenerating muscles never stains with thionin. 
