1976] 
Parsons — Morphology of Corixidae 
141 
N I) lack hydrofuge hairs while the anterior parts, which lie beneath 
the head, are covered with closely-packed short hairs. Long hairs 
are also present in the posteromedial part of the overlapped region 
in both insects. A curious feature of this region is that in both 
Diaprepocoris and Micronecta the localized spots at which muscle 
fibers attach on the pronotum are devoid of hydrofuge hairs ex- 
ternally. 
V. I-II Air Store 
Although all Hydrocorisae carry some air between the prothorax 
and mesothorax, this air space is greatly enlarged, in Hespero- 
corixa, by the very long pronotum (Parsons 1970). The I-II air 
space contains the mesothoracic spiracle (Figs. 5-7, S II). In all 
three corixids the spiracle is somewhat smaller than the meta- 
thoracic one and lies ventrolaterally in the intersegmental mem- 
brane, just ventromedial to the prealar bridge of the mesothorax. 
In Hesperocorixa, in which the spiracle is large enough to be ex- 
amined under the stereoscopic microscope, it is covered by a “sieve- 
plate” similar to that of the metathoracic spiracle (see p. 161). 
The I-II air store is directly continuous with the ventral thoracic 
and supra-alar stores. Its dorsal portion differs in the three insects. 
In Hesperocorixa (Fig. 10) the long pronotum (N I) conceals almost 
all of the mesonotum (N II). The latter has a pruinose texture like 
that of the hydrofuge parts of the forewings. The air on the meso- 
notum is largely concealed, although it is exposed along the pos- 
terior margins of the pronotum. 
In Diaprepocoris (Fig. 8) the pronotum is quite short and covers 
only the anteriormost part of the mesonotum. The exposed part 
of the latter (N II), however, has long and short hydrofuge hairs 
like those on the dorsal surface of the forewings. It probably bears 
an extensive air layer which is fully exposed to the water, rather 
than only partly exposed as in Hesperocorixa. 
The pronotum of Micronecta (Fig. 9) is longer than that of Dia- 
prepocoris but shorter than that of Hesperocorixa, and does not 
cover the posteromedial tip of the mesonotum. The scanning 
electron microscope shows that the exposed portion of the meso- 
notum, unlike that of Diaprepocoris, lacks hydrofuge hairs. The 
overlapped anterior part, however, is covered with short hairs 
except laterally and posterolaterally, in the groove which holds 
the anteromedial margins of the forewings. 
