June, '07] ENTOMOLOGICAL NEWS. 245 



cula. • Roth of these groups remained near enough like the prim- 

 itive ancestors to justify their retention in a single order or a 

 closely allied group or orders as one may wish. 



The Corrodentia, though sometimes united with the Neurop- 

 tera, are commonly separated into three or four orders as here 

 indicated, though their close relationship is coming to be very 

 generally accepted. The birdlice are most commonly segre- 

 gated as an independent order. After the general rejection of 

 the idea of the relationship of this group with the Pediculids 

 it has gradually been coming to be recognized as a recent spec- 

 ialization of a nest-infesting wingless Psocid. 



The relationships of the groups of sucking insects included 

 here in the order Hemiptera will, I think, be generally accepted. 

 The chief difference of opinion will be as to whether the groups 

 represented by Thrips and Pediadus should not be made inde- 

 pendent orders. Only a few would still further increase the 

 list of orders as indicated by the groups shown at the end of 

 this branch. 



All the groups on the right hand side in this diagram are 

 supposed to be microgenous, that is to have originated as small 

 insects, the Corrodentia entering the same habitat as the an- 

 cient Blattids and the primitive Hemiptera taking the same loca- 

 tions as the PhasmaAike forms, but leaving no early fossils 

 because of their small size and delicate structures until after 

 the groups became largely differentiated. The social white ants 

 and the few highly developed palaeozoic bugs with the sucking 

 mouthparts already perfected are all the ancient remains of 

 these groups, and in both cases they belong to groups which 

 would not be counted most ancient on anatomical grounds. The 

 venation in both the Corrodentia and the Hemiptera show a 

 profound reorganization, best explained by their simplification 

 due to small size and their reorganization when a successful 

 specialization of the body made possible a regaining of con- 

 siderable size, a specialization best accomplished in the Hemip- 

 tera. 



Leaving the groups with simple metamorphoses which were 

 differentiated in the paleozoic we find in the triassic, a Sialis- 



