BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 321 
June. As long as they were under observation, i.e., till the first part of 
July, they showed no signs of leaving the protected places about the 
fungus from which they hatched. Inasmuch as the Polyporus which 
serves the larvae as a food plant is an annual, there is probably but one 
brood during the year, the eggs not being deposited until fall. 
Thymalus is a particularly good form for histological study, inasmuch 
as material seems to be plentiful wherever there is a food supply. It is 
of convenient size and has a relatively thin cuticula at every stage. 
2. Methods. 
Since Thymalus is a small beetle, it has been necessary in studying 
the anatomy of the musculature to resort to reconstructions from sections 
in place of dissections. Material killed in hot water, or by some method 
which gave no distortion, was used, and serial sections cut 162 mw in 
thickness. To obtain a plane for reconstructiou, a “ definition appa- 
ratus ” made by Zimmermann has been used. By means of this apparatus, 
the lateral faces of the paraffin block were cut exactly perpendicular to 
each other and to the proposed plane of sectioning. ‘Two adjacent lateral 
surfaces were then painted with a mixture of soft paraffin and lampblack, 
melting at about 51° C., after which each face was again trimmed in the 
“definition apparatus” so that only a very thin layer of paint was left. 
The sections were cut on a Minot microtome in a plane perpendicular 
to that of the painted surfaces. In mounting the sections, much of the 
lampblack washes away, but, with ordinary care in the staining and 
other processes, enough adheres to the albumen affixative to give a very 
definite line at the outer edge of the lampblack area. A magnification 
of 120 diameters was used in all of the reconstructions, as this made the - 
thickness of each section equivalent to 2mm. The drawings made from 
the reconstructions have been reduced to 4 of their original size in the 
process of reproduction, so that the ultimate magnification in the plates 
is about 67.5 diameters. 
Whole and partial preparations have been used in checking the results 
of reconstruction. 
3. Anatomical Changes of the Muscles. 
Early in my study of the histological alterations of the muscles in 
Coleoptera, it was found that all of the muscles do not undergo the same 
changes. Some remain unchanged from larva to imago, many metamor- 
phose, and a few degenerate. Whether or not there were any newly 
