50 Journal of Entomology and Zoology 
having developed many specializations of their own and having lost many ancestral 
features in the process, but they appear to have departed as little as any known forms 
from the probable ancestral condition of the Coleoptera; and certain other members 
of the group to which the Dermaptera belong have retained some of the ancestral 
features which the Dermapters have lost, so that it is necessary to make a study of 
the composite characters of the group as a whole in attempting to determine what 
the ancestors of the Coleoptera were probably like. 
Before taking up the discussion of the relationship of the Coleoptera to the other 
members of the group “Panplecoptera,” it is necessary first to point out the inter- 
relationships of the insects comprising this group, and the appended diagram is 
given in order to make: these relationships more readily apparent. The primitive 
fossil Paleodictyoptera are doubtless very like the ancestors of winged insects in 
general, and some of them are quite closely related to certain members of the group 
Panplecoptera. ‘The Ephemerida are among the most primitive living representatives 
of the forms which branched off very near the base of the Panplecopteron line of 
development, but the Plecoptera are the most important of the insects actually compos- 
ing the group, having retained more of the characters occurring in the common ances- 
tral forms which gave rise to the different lines of descent of the insects composing the 
group, and their line of descent is therefore made much heavier in the diagram, to 
emphasize their importance as the nearest living representatives of the ancestors of 
the rest of the insects in the group. 
COLEOPTERA 
DERMAPTERA a 
EMBIIDAE 
PLECOPTERA 
EPHEMER1 DA 
PALAEODICTYOPTERA 
The nearest relatives of the Plecoptera are the Embiide (Sensu lato) whose line 
of development parallels that of the Plecoptera remarkably closely—in other words, 
the two groups have retained many features in common. The Dermaptera (Euplex- 
optera), among which are included the Hemimeride, have rather more features in 
common with the Embiide than with the Plecoptera, but the Plecoptera also exhibit 
many features which are retained by the Dermaptera, and I am inclined to regard 
the Plecoptera, rather than the Embiide, as the nearest living representatives of the 
ancestral forms which gave rise to the Dermapteron line of descent. As I have pointed 
out in a paper on the thoracic sclerites of immature winged insects (Proc. Ent. Soc. 
Washington, 1918) the thoracic sclerites of the Dermapteron drixenia are remarkably 
like those of certain immature Plecoptera as is also true of the head region, the nature 
of the cerci (of immature Dermaptera such as Diflatys, etc.), and many other features 
which need not be enumerated here, since I propose to take them up in another paper 
dealing with the ancestry of the Dermaptera, ete. 
