1918] Crampton—Study of Terga and Wing Bases 9 
which has been retained in the Dermaptera, but has become lost, 
or was never developed, in the Coleoptera. A suggestion of this 
fold is also retained in the Plecoptera, as is shown in the posterior 
tergal fold designated as “pt” in the metathoracic region of the 
Plecopteron depicted in Fig. 1. There is a tendency for this region 
to become reduced, or to unite with the surface which it overlaps, 
so that the narrow continuation of the surface of this fold toward 
the point designated as ‘‘x”’ in the metathorax of Fig. 4, may 
possibly be homologous with the similar narrow continuation of 
the region beside the postscutellum, toward the point labeled “x” 
in Fig. 2 (at the base of the sclerite “sa’’). 
In the foregoing descriptions, I have laid especial emphasis upon 
the resemblance between the Coleoptera and Dermaptera, as illus- 
trated by the preponderance in size of the metathorax over the 
mesothorax; the relative width, and the outlines of the nota; the 
triangular shape of the mesonotum, and its overlapping the meta- 
notum, with the consequent reduction of the mesothoracic post- 
scutellum; the development of ridges in the metanotum for holding 
the elytra in place; the formation of a transscutal suture; the 
retention of the myodisc rather than of the tegula in the metanotal 
region; the outline and extent of the pteralia, etc. Similarly, the 
marked resemblance between the Embiids and Plecoptera is shown 
in the relative size of the nota, the width and the outlines of the 
nota; the location of the prescutum in front of the anterior margin 
of the wing-base; the development of the mesothoracic postscutel- 
lum; the development of the tegulae in both segments; the elon- 
gate notopterale, ete. On the other hand, in emphasizing these 
similarities between the Coleoptera and Dermaptera. or between 
the Embiids and Plecoptera, one should not lose sight of the fact 
that the Coleoptera and Dermaptera are both related to the Em- 
biids and Plecoptera, although the Dermaptera, being the more 
primitive of the two, are nearer to the Embiids and Plecoptera 
than the Coleoptera are. 
The cerci of certain larval Coleoptera, such as Galerita janus, 
and of certain Dermaptera such as Diplatys severa (in which 
segmented cerci precede the forceps of the adult forms) are very 
similar, even when the individual segments are compared together, 
and the cerci of both groups resemble those of the Plecoptera 
extremely closely, so that the evidence of the cerci would point to 
