1976] 
Parsons — Morphology of Corixidae 
153 
Fig. 21. Diagrammatic lateral view of thoracico-abdominal region of typical 
Hydrocorisae. Hindwing, soft tissues, and abdominal tergites removed; thoracico- 
abdominal membrane (TAM), which attaches to posttergite (PT) and lateral wall 
of intersegmental ridge (IR), mostly removed. 
1970). The sclerite is recessed on the body and usually contains 
the first abdominal spiracle (S 1) which thus opens onto an enlarge- 
ment (“first abdominal spiracular chamber”, Parsons 1970) of the 
subalar air space. 
In an earlier study (Parsons 1970) I could not determine whether 
this sclerite is thoracic, abdominal, or a combination of both. 
Further investigation of a wider variety of Hydrocorisae has strongly 
indicated that the “thoracico-abdominal sclerite is a recessed, pos- 
terior part of the metathoracic epimeron, and that in most Hydro- 
corisae the first abdominal spiracle, like the metathoracic one, has 
moved from the intersegmental region into the more anterior seg- 
ment (Parsons 1972a). 
The ventral portion of the sclerite, to which the metacoxal mem- 
brane attaches (Fig. 21, MM), is weakly evaginated in such Hydro- 
corisae as Belostoma (Belostomatidae), Nepa (Nepidae), Ambrysus 
(Naucoridae) and Pelocoris (Naucoridae). The evagination is 
much larger and more prominent in the Corixidae examined here 
(Figs. 22-24, EML). This suggests that the evaginated portion is a 
