100 PALEONTOLOGY 



exhibit features ancestral to the Trichoptera and Lepidoptera on 

 the one hand, and which ally them with the Mecoptera on 

 the other. The Triassic Mesopsychida^ (forming the order 

 Paratrichoptera of Tillyard) combine characters which suggest 

 that they are on the Hue of descent of the Protodiptera. The 

 true Diptera, however, liave no known annectant forms con- 

 necting them with the Protodiptera. 



Among Hymenoptera the venation is specialised to a degree 

 wliich proclaims the singularly isolated position of the order. 

 Even among the most primitive of the saw-flies there is no indication 

 of apparent relationship with any other orders. 



The Protelytroptera (Tillyard, 1931) are a tegmen-bearing 

 order whose affinities are far from clear. That they bear an 

 apparently close resemblance to the Dermaptera as regards the 

 hind wing is obvious : furthermore, pentamerous tarsi are also 

 found in the Jurassic earwig Protdiplatys Mart, from Turkestan. 

 It is probable that they are to be regarded as early forerunners 

 of the earwigs, and according to Carpenter (1933) the venation 

 of the tegmina suggests their derivation from certain Blattids of 

 Upper Carboniferous date. The venation of both the tegmen and 

 hind wings is more specialised than that of the Protocoleoptera 

 and Tillyard's suggestion that the last-named order may prove a 

 remnant of the Protelytroptera — at a stage when the elytra were 

 still tegmen-like and flattened — seems to be in harmony with the 

 facts at present available. The scanty remains of Protocoleoptera 

 so far discovered, however, scarcely warrant any but very tentative 

 conclusions being drawn. 



The conclusions to be derived from recent advances in insect 

 palaeontology may be briefly summarised as follows : — 



1. At least nine recent orders are known to have existed from 

 Palaeozoic times. Of the remainder, the Trichoptera, 

 Hymenoptera and Diptera are known from Jurassic strata, while 

 the Thysanura, Isoptera and Lepidoptera have, so far, only 

 been traced back to the Tertiary period (Table I, p. 101). 



2. Three recent families have persisted apparently from 

 Palaeozoic times, viz., the Podurida? (Collembola) from Middle 

 Devonian ; the Blattidae sen. lat. (Orthoptera) from Upper 



