590 MESOZOIC INSECTS OF QUEENSLAND, iv., 



advanced far enougli to be considered a definite Heteropteron 

 of a primitive type. 



Let lis now consider the very interesting question of the 

 evolution of the dividing line between corium and membrane in 

 the Suborder Heteroptera. Dunstania shows us this h'ne in an 

 exceedingly primitive condition. From it, we see that its 

 anterior portion was originally composed of either branches of 

 main veins, or cross-veins. But, as the main veins are all pro- 

 ceeding more or less distad, it is, therefore, inevitable that these 

 various parts should meet at difterent angles, as we see so de 

 finitely shown in Dunstania. 



The parts of the dividing line may be shown as follows, start- 

 ing from the node or costal end (see Plate lix., fig. 15, and Text- 

 figs. 18-1 9):— 



A. Anterior Division, formed from cross-veins and branches 

 of main veins : 



1. The node, formed from the fused C and Sc. 



2. Radial portion, formed from short parts of Rj and R.^, 



partially fused together. 



3. A short cross-vein connecting the radial portion with the 



median portion. 



4. Median portion, consisting of a swollen root on M, from 



which the three branches of M are given off. 



B. Posterior Division, consisting of a sinuous line crossing the 

 wing more or less transver.sely, and not carrying either cross- 

 veins or parts of main veins : 



5. Medio-cubital portion, from the swollen root of M to Cu; 



the curvature of this part is concave to the corium. 



6. Cubito-anal portion, from Cu to the antinode; the curva- 



ture of this part is slightly convex to the corium. 



In the evolution of such a type as a recent Lygseid or Penta- 

 tomid Bug, all these diverse parts have to become aligned and 

 fused into one harmonious whole. Probably a careful study of 

 existing types amongst the Heteroptera would reveal many traces 

 of the method by which this change has been brought about. 



The other point of outstanding interest in the evolution of the 

 Heteropterous hemelytron is the development of the clavus, 



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