1918] Cram-pton — Study of Terga and Wing Bases 5 



The Plecoptera, with the Embiids, are very hke the ancestors of 

 the insects comprising this superorder, (the Panplecoptera) while 

 the Derniaptera form an offshoot which approaches the Isoptera 

 in many respects — but the strongest affinities of tlie Isoptera seem 

 to be on tlie side of the forms comprising the superorder Pandic- 

 tyoptera (composed of the Isoptera Zoraptera, Blattids and Man- 

 tids). The Coleoptera have branched off very near the Der^iiap- 

 tera, and have retained certain ancestral features occurring in the 

 Embiids and Plecoptera, but their line of development has appar- 

 ently paralleled that of the Derniaptera quite closely. Some 

 representatives of the Coleoptera exhibit certain features sugges- 

 tive of those found in the Blattids; and other Coleoptera have 

 retained certain structures (particularly in the larval stages) sug- 

 gestive of Neuropteron affinities. However, since both the Pan- 

 plecoptera and the Pandictyoptera are descended from common 

 ancestors (which were not unlike the fossil Palaeodictyoptera) it is 

 not surprising that certain features inherited from their common 

 ancestors, should be carried over into both groups; and similarly, 

 since both the Panplecoptera and the insects grouped about the 

 Neuroptera were descended from similar ancestors (the ancestors 

 of the Neuroptera were probably very similar to the Plecoptera) it 

 is not surprising that similar characters should reappear in both 

 the Neuroptera and Coleoptera. At any rate, the closest affinities 

 of the Coleoptera seem to be with the Dermaptera, rather than 

 with the Neuroptera (or with the Blattids) so far as the adult 

 characters are concerned. 



The Embiids are extremely closely related to the Plecoptera, as 

 is shown by the character of their thoracic sclerites, legs, etc. ; and 

 the fact that the cerci of the Embiids are reduced, does not militate 

 against the argument for the close relationship between the two 

 orders, since certain Plecoptera also have the cerci reduced to two 

 segments. 



In both Embiids and Plecoptera, the body is more elongate, and 

 the tergal region of the wing-bearing thoracic segments shows a 

 marked tendency toward becoming longer than broad, in contra- 

 distinction to the condition found in the Coleoptera and Dermap- 

 tera, in which the tergal region exhibits a tendency to become 

 broader than long, as may be seen by comparing Figs. 1 and 3 wnth 

 Figs. 2 and 4. In the Embiids and Plecoptera, there is a prescutal 



