EVOLUTION OF INSECTS — CARPENTER 347 



are either laid in large capsules or else they hatch and form nymphs 

 in the body of the female parent. The ovipositor in some of the 

 Carboniferous species indicates a very different method of egg laying. 



From this survey of the Carboniferous fauna it is apparent that 

 the insects had acquired surprising diversity and specializations by 

 the Upper Carboniferous period, though some really generalized 

 species were also included. Nevertheless, I am convinced that we 

 have not yet begun to appreciate the extent of the Upper Carbonifer- 

 ous insect fauna. This conviction is based in part on the nature of 

 the fauna in the lowest Permian strata and in part on the known 

 diversity of the Carboniferous insects, even though represented by 

 relatively few species. If the same number of living species were 

 collected at a few isolated localities over the world, we could not 

 expect to obtain from them a good idea of the complexity of the 

 world fauna as it exists today. It is not beyond the limits of pos- 

 sibility, therefore, that the extinct orders of Carboniferous insects 

 were in their time comparable in extent to the major orders now 

 living. 



The insect fauna of the early Permian period was distinctive, for 

 it was a combination of nine extinct orders and seven living ones. 

 None of the extinct orders, except the Protodonata, are known to 

 have lived beyond the Permian. The Palaeodictyoptera and Pro- 

 tohemiptera had apparently reached their maximum development in 

 the Upper Carboniferous, only a very few having been found in 

 Permian strata. The Megasecoptera, on the contrary, flourished all 

 through the period. The Protodonata, also, were more numerous 

 than in the preceding period, and very large species, like those pre- 

 viously noted, have been found in Permian beds in Kansas, Okla- 

 homa, and several parts of Europe. Since no flying vertebrates were 

 yet in existence, these large predatory insects must have ruled the 

 air for many millions of years, for they persisted well into the Meso- 

 zoic. They may have been an important factor in the extermination 

 of soft-bodied and weak-flying insects, such as the Palaeodictyoptera 

 and Megasecoptera. The Permian Protorthoptera continued to show 

 diversity of form. Among them, for example, are some whose cerci 

 or posterior appendages in the male were modified to form pincers, 

 or claws, resembling those in some of the living Orthoptera. 



Three additional extinct insect orders make their first appearance in 

 the early Permian. One of these, the Protelytroptera, which were 

 related to the earwigs, were the first insects known to develop true pro- 

 tective forewings, or elytra; also the hind wings were greatly ex- 

 panded and contained hinges which enabled the wings to fold up be- 

 neath the overlying elytera. Another extinct order of the early 

 Permian, the Protoperlaria, was related to the stoneflies; the adults 

 were generalized with prothoracic wing flaps, but the nymphs were 



