44 ENTOMOLOGICAL NEWS. [Feb./IQ 



they have become rather highly specialized), and it is to the 

 living forms that the following discussion is largely limited. 



The Plecoptera appear to be a "synthetic" group combining 

 in themselves a number of features which are carried over in- 

 to the other lines of development by the more primitive rep- 

 resentatives of each group. The Lepismid-like head, the 

 primitive wings, thoracic sclerites and appendages (even the 

 trimerous tarsi may prove to be more primitive than the penta- 

 merous type) and the nature of the abdominal region with its 

 appendages, not to mention the primitive condition of the 

 nervous system, alimentary tract, and other internal struc- 

 tures, all point to the fact that the Plecoptera have departed 

 as little as any living forms from the probable ancestral con- 

 dition of the forebears of the higher groups, and the palaeon- 

 tological record is in full accord with this view. As is indi- 

 cated in the diagram, the Embiidae are extremely closely re- 

 lated to the Plecoptera, and the Dermaptera are closely re- 

 lated to both Embiids and Plecoptera, although they seem to 

 have somewhat more in common with the Embiids than with 

 the Plecoptera. These three orders, together with the 

 Coleoptera, constitute the superorder Panplecoptera. Certain 

 Palaeodictyoptera such as Stenodictya exhibit a number of 

 features which have been retained by certain members of the 

 superorder Panplecoptera, and it is quite possible that some 

 fossil forms such as the Haplopteroidea or Hadentomoidea 

 might be included in this superorder also ; but too little is 

 known of the structural details of most of these fossil insects 

 to enable us to definitely determine their closest affinities in 

 the present state of our knowledge of their anatomy which 

 seems to be confined largely to wing-veins ! 



The P>lattidae are regarded by most investigators as the 

 lowest living representatives of the group to which they be- 

 long, and their type is undoubtedly an extremely ancient one ; 

 but I am by no means certain that the Blattidae are so much 

 more primitive (anatomically) than the Isoptera, as some 

 palaeontologists would have us believe. The opisthognathous 

 head, which is typical of the Blattids as a whole, is certainly 



