266 INSECT TRANSFORMATION 



the Hemiptera, associated with the primitive palaeodictyo- 

 pteroid type of wing ; even if Eugereon cannot be regarded as 

 on the direct line of ancestry of living Hemiptera, it suggests 

 clearly that this order had a common origin with the exoptery- 

 gote biting insects. In Russian Upper Permian rocks there 

 have been found fossil remains of an insect (Prosbole), with 

 forewings in which the basal and terminal regions are im- 

 perfectly differentiated as corium and membrane, so that it 

 may be referred to a sub-order (Palaeohemiptera) intermediate 

 in character between Heteroptera and Homoptera. Fossils 

 from the same geological horizon, both in Russia (Scytinoptera) 

 and in New South Wales (Permoscarta) may be safely regarded 

 as ancestral Homoptera, 1 and in Triassic times there were 

 already differentiated the main family groups of Homoptera 

 as we know them to-day. At the same period a primitive 

 family (Dunstantiidae) of the Heteroptera was also estab- 

 lished, while in the subsequent Jurassic period specialized 

 families of Heteroptera both terrestrial (Reduviidae and 

 Lygaeidae) and aquatic (Gerridae and Belostomidae) are 

 represented by well-preserved fossils. The divergence between 

 Heteroptera and Homoptera as regards life-history has already 

 been recalled ; it is interesting to note that one of the most 

 dominant of modern homopterous families, the Aphididae, 

 retains a type of life-history like that of the Heteroptera with 

 little or no transformation. This family belongs to the same 

 section of the sub-order as those families the Aleryrodidae 

 and Coccidae which display the most remarkable transforma- 

 tions of any exopterygote insects (pp. 86-90). It is probable 

 that this section of the Homoptera diverged from the rest of 

 the sub-order in Permian times, though we have no direct 

 fossil evidence of this. 



Turning now to the Endopterygota or insects that undergo 

 complete transformation with a pupal stage, we have already 

 (pp. 260-1) adduced evidence from the striking correspon- 

 dences in the larvae and pupae of various orders that this 

 sub-class forms a natural group with a common origin from the 

 primitive Exopterygota. In correlation with this view, it 



1 R. J. Tillyard : " Mesozoic Insects of Queensland : " Hemiptera 

 Heteroptera ". Proc.Linn.Soc. N.S. Wales, XLIII, 1918 ; and " Hemiptera 

 Homoptera ", Id. XLIV. 1919. 



