62 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



wood and bark boring larvae that are most frequently met with 

 by investigators and sent in by correspondents. 



"I think that we will find the principal distinguishing characters 

 in the head and mouth parts but these must be correlated with 

 thoracic and abdominal characters. Therefore we need a more 

 exact knowledge of the primary external elements of structure and 

 a key to such of the so-called homologous elements as are of the 

 greatest taxonomic value. 



"In my work on the anatomy of Dendrodonus, I found that 

 the pleural suture was of fundamental importance as a guide to 

 the location and identification of elements of structure in the 

 adult, pupa and larva (Technical Series 17, part 5, Bureau of 

 Entomology, 1909, fig. 9, 38, 39). In the work carried on by Mr. 

 Snodgrass and myself on the thorax of insects we found that the 

 key to the structure of the pleurum in adult insects was -the pleural 

 suture (Proc. U. S. N. M., vol. xxxvi, 1909, p. 536, fig. 3). Now 

 with the additional facts revealed by Doctor Boving relating to the 

 musculatory system of the abdominal segment in coleopterous 

 larvae, I am convinced, that the pleural suture is the key to the 

 structural modification and homology of the pleurum in all seg- 

 ments of all stages of insects, and therefore largely a key to the 

 morphology of the hexapodal type. 



"All of this shows that the essential features in the development 

 from the egg to the adult in the insects with a so-called incomplete 

 metamorphoses is not so very different from those in insects with 

 a so-called complete metamorphoses. Therefore rnu^h of the 

 terminology, as applied to the primary elements of the adult, is 

 applicable to all stages, such as the tergum with its prescutum, 

 scutum, scutellum and postscutellum, the sternum with its pre- 

 sternum, sternum, sternellum and poststernellum ; the pleurum with 

 its epipleurum and hypopleurum ; the epipleurum with its epimeral 

 area, lobe or sclerite and its spiracle area, lobe or membrane; the 

 hypopleurum with its episternal area, lobe or sclerite and its coxal 

 area, lobe or coxa and so on as applied to all body segments of 

 all stages. 



"It must be kept in mind, however, that there is an almost 

 unlimited range of modification in each and all of the named 

 elements. There is often a most complex subdivision of one, the 



