1976] 
Parsons — Morphology of Corixidae 
157 
provides an attachment for the metacoxal membrane (Figs. 18 and 
22, MM). Although the intersegmental boundary is not indicated 
by any definite landmark on the sclerotized strip, comparison of 
Diaprepocoris with Micronecta (Fig. 23, IR) and Hesperocorixa 
(Fig. 24, IR) strongly suggests that the boundary runs lengthwise 
along the structure, paralleling the attachment of the thoracico- 
abdominal membrane. 
The muscle process (Figs. 18 and 22, MP) which lies at the pos- 
teromedial end of the sclerotized strip projects anterodorsally. 
A large muscle attaches to its anterior face and extends dorso- 
medially to the medial portion of the first abdominal tergite. This 
suggests that at least the anterior portion of the process represents 
the first abdominal segment, and that the thoracico-abdominal 
boundary passes anteromedial to its base. 
The muscle process, unlike that of Micronecta (Fig. 23) or 
Hesperocorixa (Fig. 24) is separated, by a membrane, from the 
anteroventral portion of the abdomen. An irregularly shaped 
medial arm of the process articulates flexibly with the anterior wall 
of a low second abdominal antecosta (Fig. 22, AC2); this narrow 
anterior wall appears to represent a reduced first abdominal sternite. 
The rest of the muscle process is separated, by a narrow strip of the 
thoracico-abdominal membrane, from the part of the abdomen 
containing the second abdominal spiracle (S2). The latter region 
lacks a second abdominal antecosta and appears to consist only 
of the second abdominal segment. Laterally it forms the abdominal 
projection (AP). The dorsal portion of the thoracico-abdominal 
membrane, which attaches to the abdominal projection, contains 
the sensory membrane of the first abdominal scolopophorous organ 
(SO 1). This sense organ, like the metathoracic one (SO III), was 
not examined here; the small sclerite to which its scolophore prob- 
ably attaches does not appear to be unusually modified. 
III. Micronecta 
The metathoracic epimeral lobe and the second abdominal spira- 
cle of Micronecta, unlike those of Diaprepocoris and Hesperocorixa, 
are concealed ventrally by the metathoracic episternum (Fig. 6, 
ES III), whose posterior lobe is longer than in the other two insects. 
As in Diaprepocoris, the epimeral lobe (Figs. 19 and 23, EML) is 
a two-walled structure lying posteroventral to the metathoracic 
coxal process (Figs. 19, PR; Fig. 23, heavy black dot). The lobe 
differs from that of Diaprepocoris, however, in the shape of the 
