Insects of Past Ages 353 



race of insects with the general build and appearance 

 ot modern Cockroaches (l}, but with transparent 

 fore-wings, the hind-wings being similar and without a 

 folding anal area. The wing-neuration is of a 

 simplified orthopterous type, five principal longi- 

 tudinal nervures being present in both fore and 

 hind-wings ; in the fore-wings of modern cock- 

 roaches the number is reduced to four though the 

 hind-wings retain five. A wing-fragment with similar 

 orthopteroid neuration has been discovered in the 

 Silurian rocks of northern France ; this is the oldest 

 insect-fossil known to us. 



In Secondary rocks — Triassic and Liassic — remains 

 are found with wings intermediate in structure be- 

 tween those of the Carboniferous types and those of 

 modern Cockroaches, the differentiation between the 

 fore- and hind-wings having begun. It may be re- 

 garded then as certain that our living Orthoptera are 

 the specialised descendants of insects of the Primary 

 epoch, with four similar membranous wings. For 

 not the Blattidse only, but the Phasmids and Locus- 

 tidse appear to have had, in Carboniferous times, 

 ancestors whose fore-wings had not yet become firm 

 in texture and whose hind-wings had no folding 

 anal area. We find therefore that if the insects of 

 the Primary epoch be taken into account the main 

 distinction between Orthoptera and Platyptera^ breaks 

 down, and we are able with confidence to look back 

 to common ancestors for both orders, probably with 

 simple body-form like a modern termite, four similar 



1 On account of the similarity of their two pairs of wings it has 

 been proposed (203) to class all Palzozoic insects Ln a special order — 

 PalzodictToptera. As these insects, however, are clearly related to 

 existing families of our Orthoptera and Platjptera '205 it is better 

 either to distribute these extinct families according to their affinities 

 between those two orders, or to unite the living Orthoptera. Platyp- 

 tera and the fossils, into one single order. 



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