318 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
has been undertaken with the purpose of aiding, if possible, in the ex- 
planation of some of these alterations, and thus to untangle the confusion 
in regard to them. A detailed study has been made on Coleopterous 
material, since beetles were found to present a fairly simple metamor- 
phosis of the muscular system. 
These changes naturally fall into two groups; the anatomical and the 
histological. Previous papers on this subject have ignored almost com- 
pletely the anatomical side of the question. This one-sided method has 
been responsible for much of the confusion which has arisen. 
In connection with this neglect of the study of the anatomy of the 
muscles, most authors have assumed that all of the muscles of any one 
insect undergo similar changes during pupal life. Yet, it is conceiv- 
able that any one of, or any combination of, the following conditions may 
be found in a single holometabolic insect : | 
a. The larval muscles may not be changed, but pass unaltered into the 
imago. 
b. The larval muscles may undergo a more or less complete metamor- 
phosis into the imaginal muscles. 
c. The larval muscles may degenerate entirely, and the imaginal 
muscles form anew in the pupa. 
As the results of this research show that a combination of these three 
methods is found in Coleoptera, and as the remaining orders of metabolic 
insects are probably fundamentally like Coleoptera, it is not strange that 
contradictions have arisen. It is possible that two investigators, even 
though working on the same species, have, in studying different muscles, 
studied different conditions. 
This investigation was undertaken at the suggestion of Dr. E. L. 
Mark. During the three years that I have been engaged in the work, 
he has constantly aided me by his advice and criticism. To him, my 
heartiest thanks are due. I also wish to express my thanks to Mr, 
Samuel Henshaw, of the Museum of Comparative Zodlogy, for his many 
kindnesses. 
Part I.— Anatomy. 
A. HIstoricaAL SURVEY. 
The dissections of the muscular system of insects are not very numer- 
ous, and, as the homologies of the muscles are difficult to determine, the 
comparative myology of insects is not in a very satisfactory condition. 
Those investigations which have been published are, with few exceptions, 
