1976] 
Parsons — Morphology of Corixidae 
149 
Fig. 19. M. sedula; internal view of pterothorax and anterior abdomen, cut 
parasagittally lateral to mesocoxa. Cross-hatched cut edge of mesothoracic pleural 
ridge (PL II) indicates base of pleural apophysis (removed). Metacoxa and soft 
tissues removed; part of inner wall of metathoracic epimeral lobe (EML) cut away 
to show indented portion (C) of outer wall of lobe. 
The lateral lobe is so wide that its base (Figs. 19 and 20, B) lies 
immediately lateral to the mesothoracic pleural apophysis (Fig. 
14B, PL II; Figs. 19 and 20, cross-hatched part of PL II). In mature 
specimens of both corixids the base of the lobe adheres closely to 
the pleural apophysis and can be dissected away from it only with 
difficulty. In Micronecta the base of the lateral lobe is marked by 
a groove, on the external surface of the epimeron, which extends 
posteriorly as far as the ostiole of the metathoracic scent gland 
(Fig. 16, O). The mesothoracic pleural sulcus of Hesperocorixa, 
like that of Diaprepocoris, is complete and extends from the meso- 
thoracic coxal process to the pleural wing process. In Micronecta, 
however, the sulcus is incomplete and can be clearly distinguished 
only in the region of the pleural apophysis (Fig. 19, cross-hatched 
portion of PL II). 
All three corixids possess a metathoracic scent gland and a paired 
efferent system which carries the secretion from the dorsal surface 
of the metasternal xiphus (Figs. 5-7, X) to an ostiole at the posterior 
