1920] Crampton — Lines of Descent of Lower Winged Insects 117 



domen, and in an article in the May, 1920, issue of the Proceedings 

 of the Entomological Society of Washington (Vol. 22, p. 98) these 

 insects, together with their immediate relatives {i. e., the Pro- 

 tephemerida, Ephemerida, Protodonata, Odonata, certain of the 

 Palaeodictyoptera, etc.), were grouped in an ancestral superorder 

 of insects called the Panpaleeodictyoptera, or Panplectoptera (from 

 Packard's term "Plectoptera," applied to the Ephemerida). The 

 lines of development of these insects are shown in Fig. 1, although 

 all of the fossil forms are not represented in the diagram. 



As is indicated in Fig. 1, the fossil Palseodictyoptera occupy a posi- 

 tion at the base of the lines of descent of other winged insects, and 

 have apparently departed as little as any known forms from the 

 first types of winged insects to be evolved. Some of the insects 

 usually included in the order Palseodictyoptera are apparently 

 more closely related to the insects grouped about the Plecoptera, 

 and should be included in the next superorder (Panplecoptera) . 



ODONATA 

 PROTODONATA 



EPHEMERIDA 

 .PROTEPHEMERIDA 



.PALAEODICTYQPTERA 



Fig. 1. Lines of descent of the Panplectoptera. 



The Ephemerida are in some respects intermediate between the 

 Palseodictyoptera and the Plecoptera (together with certain other 

 forms), and they also exhibit certain archaic features carried over 

 from their Apterygotan forebears — for winged insects were un- 

 doubtedly derived from ancestors closely resembling the Lepis- 

 midse and other Apterygota, and could not possibly be derived 

 directly from the Trilobita as Handlirsch would have us believe! 

 The Ephemerida have also retained certain features suggestive of 

 Crustacean affinities, and a study of their anatomy (particularly of 

 the immature stages) is of considerable value in tracing the evolu- 

 tion of the higher forms. Handlirsch considers that the Ephemerida 

 were derived from the fossil Protephemerida, and that the Odonata 



