58 PROC. ENT. SOC. WASH., VOL. 20, NO. 3, MAR., 1918 



from the fact that both Ephemerid and Odonatan adults appear 

 to be somewhat related; but the Odonata have apparently fol- 

 lowed a strongly aberrant course of development, and their 

 sclerites also differ markedly from those of other insects. 



From the study of other structures, I had been led to expect 

 that the sclerites of larval Coleoptera would resemble those of 

 nymphal Euplexoptera and Plecoptera very closely; but the re- 

 semblance to the condition found in the Neuroptera is much 

 greater, in the Coleoptera here figured, as can be seen by compar- 

 ing figure 21 with figure 18. The condition found in some Coleop- 

 terous larvae (fig. 5) is rather suggestive of that found in the larva 

 Corydalis (fig. 4), while that found in other Coleopterous larvae of 

 (fig. 7) bears a rather strong resemblance to the nature and ar- 

 rangement of the sclerites in the larva of the Neuropteroid insect 

 Rapkidia (fig. 6). The insects of the order Coleoptera, however, 

 exhibit such different types of larvae, and the range of modifica- 

 tions met with in the nature and arrangement of their sclerites 

 - is so great, that I feel confident that some Coleopterous larvae 

 will be found, in which the sclerites will bear a strong resemblance 

 to those of the nymphal Euplexoptera and Plecoptera; although 

 it must be admitted that thus far the evidence obtained from 

 the study of the sclerites of the larvae would point to a closer re- 

 lationship between the Coleoptera and the Neuropteroid insects. 

 Indeed, the nature of the narrow transverse jugular plates of 

 figures 4 and 6, which is characteristic of many Neuropteroid 

 larvae, is the only absolute feature in the thoracic sclerites which 

 would clearly distinguish the larval Coleoptera from the larval 

 Neuropteroid insects here studied. 



The condition of the sclerites of the Homoptera (fig. 1) is 

 quite similar to that of the Neuroptera (fig. 18), as might be ex- 

 pected from the fact that adult Homoptera have retained many 

 features suggestive of their descent from ancestors resembling 

 the Neuroptera.' The sclerites of nymphal Homoptera likewise 

 resemble those of larval Coleoptera, in some respects, as might 

 be expected if the Coleoptera are also closely related to the 

 Neuroptera. 



It is a rather surprising fact that, so far as the thoracic scler- 

 ites are concerned, the larvae of the Trichoptera (fig. 19) resem- 

 ble the larvae of tne Neuroptera (fig. 18) more than the larvae 

 of the Panorpids (fig. 23) do, since su<ph Neuropteroid insects 

 as Nemoptera occupy a position somewhat intermediate between 

 the Panorpids and other Neuroptera. Until the larvae of 

 Nemoptera and suchp rimitive Panorpids as Merope, Panorpodes, 

 etc., are available for study, it is extremely unsatisfactory to 

 attempt to draw any further conclusions concerning the inter- 

 relations of the Trichoptera, Panorpids and Neuroptera from the 



