98 PALEONTOLOGY 



probability that the latter order had a common ancestry with 

 the other Exopterygota mentioned. The most primitive true 

 Hemiptcra occurred as early as Lower Permian times, and their 

 most ancient families are referable to the sub-order Homoptera. 

 The oldest of the Heteroptera are the Dunstaniidse, from the 

 Upper Trias, but palaeontology has not so far shed much light on 

 their derivation and relationships with the Homoptera. The only 

 evidence so far revealed is the discovery of an upper wing in the 

 Trias of Queensland belonging apparently to the Homopterous 

 family Scytinopteridte (Auchenorrhyncha). According to Tillyard 

 (1936) this specimen shows evidence of transformation into a 

 true Heteropterous tegmen. 



Discoveries of Lower Permian Homoptera, belonging to the 

 extinct family Archescytinidae, have demonstrated venational 

 affinities with early types of Psocoptera found along with them. 

 It appears likely that the Hemiptcra and Psocoptera are divergent 

 developments from a common stock and that, later on in geological 

 time, the Anoplura were evolved as descendants of wingless 

 Psocids which had become adapted for a parasitic life upon 

 warm-blooded vertebrates. 



Mention has been previously made of the resemblance between 

 certain of these early Psocids and the Embioptera. If this 

 reveals anything more than parallelism, or convergence, we may 

 have to seek for the ancestry of the last-mentioned order in this 

 direction. The palseontological history of the Embioptera, 

 however, is so scanty that their ancestry remains enveloped in 

 obscurity, and no undoubted evidences of the order occur until 

 the Tertiary period. The Isoptera similarly have left no certain 

 indications of their ancestry. Structurally, they betray very 

 evident Blattoid characters and there is little doubt that they 

 arose from cockroach-like forms which subsequently developed a 

 complex social organisation. In Tertiary times their genera were 

 very much as w^e find them to-day, and it is evident that ancestral 

 forms will have to be sought in rocks of considerably earlier date. 

 Palaeontology likewise reveals nothing with respect to the affinities 

 of the Thysanoptera, but, from a study of recent forms, we are 

 led to conclude that they ha\'e more in common with the Hemiptcra 



