The Dermaptera and agree with the vast majority of winged insects - are the absence of distinct maxillulae and the presence of an unpaired ectodermal tube as the terminal region of the genital system in both sexes.
In the present article a short account of the characters of the Dermaptera and Orthoptera is given, while for details the reader is referred to special articles on the more interesting families or groups.
The Odonata are in many imaginal and larval characters highly specialized; yet they probably arose with the Ephemeroptera as a divergent offshoot of the same primitive isopteroid stock which developed more directly into the living Isoptera, Plecoptera, Dermaptera and Orthoptera.
The Dermaptera and the Orthoptera agree in having welldeveloped mandibles, so that the jaws are adapted for biting; in the incomplete fusion of the second maxillae (which form the labium) so that the parts of a typical maxilla can be easily made out (see the description and figures of the cockroach' g.
A description and enumeration of all known Dermaptera has been lately published by A.
Thus the condition in the Dermaptera is more primitive than in any other Pterygote order except the Ephemeroptera (Mayflies) which are still more generalized, the primitive mesodermal ducts (oviducts and vasa deferentia) opening by paired apertures as in the Crustacea.
In the vast majority of the Dermaptera the cerci are - in the adult insect at least - stout, unjointed appendages forming a strong forceps (fig.