1918] Crampton—Study of Terga and Wing Bases 5 
The Plecoptera, with the Embiids, are very like the ancestors of 
the insects comprising this superorder, (the Panplecoptera) while 
the Dermaptera form an offshoot which approaches the Isoptera 
in many respects—but the strongest affinities of the Isoptera seem 
to be on the 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 Dermap- 
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 Dermaptera 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, ete.; 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 with 
Figs. 2and 4. Inthe Embiids and Plecoptera, there is a prescutal 
