1976] 
Parsons — Morphology of Corixidae 
137 
The anteroventral portion of the abdomen is concave on each 
side of the midline, forming a pair of metacoxal indentations (Figs. 
5-7, MI) which accomodate the metacoxae and contain the second 
abdominal spiracles (S2).The metacoxae of living Hesperocorixa 
are surrounded by an air layer which extends into the metacoxal 
indentations (Parsons 1970). In all three corixids the ventral and 
posterodorsal surfaces of the metacoxae bear closely-packed long 
hairs, but these hairs are lacking on the anterodorsal coxal surfaces 
and on the metacoxal indentations in which they lie. The air in the 
indentations of Hesperocorixa, and presumably in those of the 
other two insects, must be retained by the close apposition between 
the coxae and the abdomen rather than by hydrofuge hairs. 
Fig. 6. M. sedula, ventral view, prepared as in Fig. 5. Second abdominal spiracle 
(S2) concealed by lobe of metathoracic episternum. Efferent channel (EC) of meta- 
thoracic scent gland, indicated by dotted lines, lies beneath exoskeleton. 
Fig. 7. H. interrupta, ventral view, prepared as in Fig. 5. 
