PROC. EXT. SOC. WASH., VOL. 20, .VO. 3, MAR., 191S 59 



study of the larval sclerites, since the larvae at present available 

 for study, are too highly specialized for this purpose. 



Adult Trichoptera are structurally very similar to the lower 

 Lepidoptera, and one would naturally expect that the sclerites 

 of the larval Trichoptera (fig. 19) would be very similar to those 

 of the larval Lepidoptera (fig. 20), whereas, on the contrary, the 

 sclerites of the Panorpid larva (fig. 23) seem to be much more 

 like those of the Lepidoptera (fig. 20) than the sclerites of certain 

 Trichopterous larvae are; and the same is true in regard to the 

 narrow bands representing the chitinized portions of the coxae 

 ex in both Panorpids and Lepidoptera. If one compares the 

 sclerites of a more primitive Lepidopteron larva such as that of 

 Hepialis, with the Panorpid here figured, the resemblance is 

 even more pronounced; but the Trichopteron larva shown in 

 figure 19 is possibly not as suitable for such a comparison as 

 others which were not available for study. On the other hand, 

 in comparing the ventral region of the Trichopteron larva shown in 

 figure 9, with the ventral region of the Lepidopteron larva shown 

 in figure 8, there is apparent a marked similarity in the nature 

 of the sclerites, especially with regard to the transverse sclerite 

 ss. It is impossible to make a close comparison, however, since 

 I have been unable to borrow a larval Adda for study, and figure 

 8 of this larva, was therefore taken from a figure by Forbes, 

 1910, who does not distinguish between the chitinous and mem- 

 branous region in his drawing, thus making it more difficult to 

 compare the two larvae. 



The larvae of the Tenthredinids (fig. 17) resemble those of 

 the Panorpids (fig. 23) in having retained the lateral cervical 

 plates Ic, which I have not found in any Lepidopteron larva. 

 In certain other respects, however, the sclerites of the Tenthredi- 

 nid larva bear a slight resemblance to those of the Lepidoptera 

 (fig. 20), although neither the Lepidopteron nor the Panorpid 

 larva seem to have retained a plate similar to that labeled ep 

 in figure 17, and the coxae of both are quite different from those 

 of the Hymenopteron larva. 



Conclusions based upon an examination of one set of structures 

 alone can hardly be regarded as of much value, so that the study 

 of the thoracic sclerites has been made to supplement that of 

 the various other structures of larval and adult forms in attempt- 

 ing to determine the relationships of the different groups of in- 

 sects. Furthermore, the extreme rarity of the larvae of the more 

 primitive representatives of the different groups, has made it 

 impossible to obtain this very necessary material for comparison, 

 so that the purpose of the present paper is largely that of pre- 

 senting the principal types of thoracic sclerites met with in the 

 study of the commoner forms, as a basis for the further study of 

 the various modifications met with in the different groups of insects. 



