EVOLUTION OF INSECTS — CARPENTER 345 



Table 1. — Oeological ranges of eceisting orders — Continued 



EARLIEST 

 NAME OF ORDER GEOLOGICAL RECORD 



13. Mallophaga (bird lice) [No fossils known] 



14. Hemiptera (bugs) Early Permian 



15. Anoplura (sucking lice) Pleistocene 



16. Thysanoptera (thrips) Late Permian 



17. Mecoptera (scorpionflies) Early Permian 



18. Neuroptera (ant lions, dobsonflies) Early Permian 



19. Trichoptera (caddis-flies) Jurassic 



20. Diptera (flies, mosquitoes) Jurassic 



21. Siphonaptera (fleas) Early Tertiary 



22. Lepidoptera (butterflies, moths) Early Tertiary 



23. Coleoptera (beetles) Late Permian 



24. Strepsiptera (stylops) Early Tertiary 



25. Hymenoptera (bees, ants, wasps) Jurassic 



The little-known Protephemerida require no comment here, but the 

 Megasecoptera show several unusual features. They had veiy long ab- 

 dominal cerci, lacked prothoracic flaps, and had more highly modified 

 wings and body structures than the Palaeodictyoptera. In some 

 species the wings were falcate (pi. 1, fig. 1) , in others petiolate; in still 

 others the prothorax was armed with spines. Noteworthy, also, was 

 the presence of wing markings, which are evident even in specimens 

 preserved in black shale. What «olors were originally in the wings is 

 not known, but a definite color pattern is indicated in the fossils. 



As paleopterous insects, the Megasecoptera presumably developed 

 by incomplete metamorphosis; the presence of true nymphal forms 

 definitely associated with adults, in the British coal measures, substan- 

 tiates this conclusion. It should be noted, on the contrary, that Forbes 

 [10], has expressed the belief that the Megasecoptera were actually 

 holometabolous. It is true that, although most species of Megasecop- 

 tera are found preserved in paleopterous fashion with wings outspread, 

 a. few families included species that unquestionably held their resting 

 wings over the abdomen. That these latter species represent the 

 beginnings of the true neopterous line of evolution seems very doubtful 

 to me in view of their several specializations ; also, that they represent 

 a distinct order, quite removed from the rest of the Megasecoptera, 

 seems equally unlikely. I am led to believe, therefore, that the species 

 of this order which were able to hold the wings over the abdomen 

 developed this ability independently of the true neopterous types. 



Another order of paleopterous insects, very different from the three 

 just mentioned, was the Protodonata, which closely resembled dragon- 

 flies. Like the latter, they were predaceous, and had spiny legs and 

 large mandibles. All the Protodonata were large and some members 

 of one family, with a wing expanse of 2^/2 feet, were the largest insects 



