340 bulletin: museum of comparative zoology. 



abdominal region is a curious fact of which no explanation can be 

 offered. 



The direct descent of most of the imaginal muscles from larval 

 muscles, which has here been shown, will help in solving some of the 

 difficult problems of the comparative myology of insects, — a subject 

 about which little is known. Hitherto the only basis of comparison be- 

 tween the muscles of metabolic and ametabolic insects, or between the 

 muscles of different metabolic insects, has been the origin and insertion 

 of the muscles in the imago. No attention has been paid to the larval 

 musculature, since this has been generally supposed to have no connec- 

 tion with the imaginal. But, as this paper shows, there is a close 

 connection between the larval and imaginal musculature in Coleoptera, 

 and a similar connection will probably be found to exist in most of 

 the metabolic insects. With this relation as a basis for comparisons, 

 the simpler conditions — the larval — may be used in establishing the 

 homologies instead of the more complex, — the imaginal. And this, not 

 only for comparison between different metabolic insects, but also between 

 metabolic and ametabolic insects. 



A word ouglit, perhaps, to be added to meet the possible criticism, 

 that in some of the muscles there are such radical differences between 

 the conditions in the stages figured that the identity of the various 

 muscles in successive stages is doubtful. In answer to this, it may be 

 stated that not only the stages figured, but also several intermediate 

 stages, have been studied. The dorso-ventral metathoracic muscles have 

 been identified with the help of camera sketches in four individuals in 

 stages of development intermediate between the stages used in making 

 the reconstructions. Numerous other animals have been used in which a 

 part of these muscles have been identified. The antero-posterior mus- 

 cles are much simpler, and have been identified in as many as twenty 

 cases. 



Part II. — Histology. 



A. Historical Survey. 



This review of researches on the histological changes of the muscles 

 during the metamorphoses of insects has been arranged in four parts 

 corresponding to the four principal groups of holometabolic insects. Such 

 an arrangement is used rather than a simple chronological one, because so 

 little comparative work has been done that the mutual relations of the 

 changes of the various groups are not entirely understood. The studies 



