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 Zoology, for his many 

 kindnesses. 



Part I— Anatomy. 



A. Historical 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, 



