1927] Thoracic S clerites and Wing Bases of the Roach 65 
segments (in which the postscutellum is formed behind the 
eunotum or wing-bearing plate). The small anterior margin of 
the mesonotum bearing the label pm in Fig. 16 may be considered 
as a posterior portion of the prothorax, since, as Dr. Snodgrass 
points out, the phragmas represent the lines of demarcation be- 
tween the segments dorsally, and the area pm of the mesonotum 
(Fig. 16) lies in front of the phragmas (or internal structures for 
muscle attachment, whose location is indicated by the pits ppt 
of Fig. 16) and should therefore be reckoned to the prothoracic 
region, although it is borne on the anterior margin of the meso- 
notum. 
In the meso- and metanotal region, the wing bearing plate, 
or eunotum, is divided into the following regions. The anterior- 
most sclerite, or pretergite, of Fig. 16, is an ill-defined region 
bearing the phragmal pitts ppt which mark the location of the 
internal ridges or phragmas ph of Fig. 13, for example, and these 
phragmas or phragmal ridges delimit the segments dorsally, so 
that the anterior marginal region pm of the pretergite being 
anterior to the phragmas, belongs to the segment in front, as 
was mentioned above. In the mesonotum of the roach (Fig. 16) 
the prealar sclerite pra becomes detached from the lateral region 
of the pretergite prt, while in the mesonotum of the mantid 
shown in Fig. 6, the region pra forms an incomplete prealar 
bridge, which is well developed in such insects as the Plecoptera, 
etc. In the metanotum of the roach (Fig. 16) the prealar sclerite 
pra does not become detached (as it does in the mesonotum) but 
it bears a pit like that labelled pp in the prealar sclerite pra of the 
mesonotum. The anterior margins of the sclerites prt and pra 
apparently become involved in the formation of the postscu- 
tellum of the segment in front, when the postscutellum is en- 
larged through further chitihization and pigmentation of the 
“intersegmental” membrane to form the large postscutellar plate 
of other insects 
The faintly demarked median region labelled psc in the 
mesonotum otf the roach (Fig. 16) corresponds to the prescutum 
of the mantid shown in Fig. 6, and represents the second im- 
portant area demarked in the eunotum (or wing-bearing plate). 
The regions labelled pn2 and pnS in the meso- and metanotum 
