62 Bulletin of the Brooklyn Entomological Society Vol. XIII 
The ventral portion of the tenth abdominal sternum or its 
homolog which is prolonged posteriorly beneath the genitalia 
forms the hypandrium or hypoproct “hy” of all figures. This 
plate is sometimes termed the subgenital valve, subgenital plate, 
subanal plate, etc., but the true subgenital plate is the eighth 
ventral segment prolonged below the ovipositor of the female, and 
is so used in papers on the genitalia of female insects (Crampton, 
1917), so that I prefer to designate the plate labeled “hy” in all 
figures as the hypandrium. A posterior prolongation of this 
plate forms a “prow” or “stern” in some insects (Figs. 10, 16, 
60, 64, etc., “ po”), and is of some value in classification. 
The plate “hy” of winged insects is possibly made up, in 
part, of the united structures labeled “hy” in the Lepismid 
shown in Fig. 94, which are supposed to represent the basal por- 
tions (“coxe”’) of the abdominal legs united with the sternum. 
Traces of the two structures “hy” of Fig. 94 may possibly be in- 
dicated by the lateral regions labeled “hy” in the roach shown in 
Fig. 92. The outline of the hypandrium is a feature of consid- 
erable importance in the classification of the Blattids. 
The hypandrium “hy” bears a pair of segmented styli or arthro- 
styles labeled “s” in Fig. 9 of an Ephemerid. These segmented 
styli are called “ gonopods” by some students of the Ephemerida, 
and in some saw-fly larve they have been referred to as “ cerci.” 
A comparative anatomical study, however, would indicate that the 
structures in question are merely segmented styli (or arthrostyles) 
which are composed of several segments in certain lower forms; 
but are one-segmented in most insects in which they are retained, 
and even in some of the Ephemerids, such as the one shown in 
Fig. 4, these styli ““s” are composed of but one segment. 
The styli are present in many male Blattids, being of consider- 
able length in such forms as Periplaneta (Fig. 77, “s”’), while 
they are quite rudimentary in such forms as Baliella (Fig. 96, 
“s”) in which it is very difficult to make them out. In the latter 
roach, the plate “hy ” is quite asymmetrical, and the styli “s” are 
unequally developed. 
The styli “s” are quite well developed in certain male Man- 
tids (Figs. 70 and 71), and are fairly large in some Orthoptera 
(Fig. 76, “s”), while in others (Fig. 60, “s”), they are greatly 
