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Psyche 
[June 
latter method is possible it is, in my opinion, more probable that 
they contact the surface anterodorsally. Diaprepocoris and Micro- 
necta resemble Hesperocorixa, and differ from other Hydrocorisae, 
in the presence of an air store beneath the posterodorsal margin of 
the head. All three insects also possess an air store on the meso- 
notum. Both air stores would tend to increase the buoyancy of the 
anterodorsal part of the body in Diaprepocoris and Micronecta, 
and if this region contacted the water surface the air could pass 
directly into these two air stores. Wroblewski (personal communi- 
cation) has pointed out that the posterior margin of the head of 
Micronecta is raised at the midline (Figs. 9 and 12), forming a 
funnel-like space through which atmospheric air might enter. It 
is possible that Diaprepocoris can contact the water surface any- 
where along its dorsal surface, owing to the buoyancy of its exten- 
sive supra-alar air store. Notonecta (Notonectidae), which also 
has a large supra-alar air store, contacts the water surface postero- 
ventrally rather than dorsally. However its ventral air store, unlike 
that of Diaprepocoris , is held by hydrofuge hairs which are much 
longer than those on the forewing, and its ventral surface is thus 
more buoyant than its dorsal surface. 
In Hesperocorixa the atmospheric air which enters the cervical 
and I-II air spaces is moved posteriorly, along the emboliar and 
ventral air stores, by the middle and posterior legs (Parsons 1970). 
Both these air stores are exposed to the water and can obtain dis- 
solved oxygen. The ventral and supra-alar air stores communicate 
with the subalar one along the lateral edges of the abdomen and 
at a gap (Fig. 13, arrow) between the forewing and the metathoracic 
epimeral lobe (Parsons 1970). Thus the subalar air store, in which 
the metathoracic and first abdominal spiracles lie, can receive 
both atmospheric oxygen and dissolved oxygen. The subalar 
spaces of both Diaprepocoris and Micronecta could receive oxygen 
in a similar manner. In both insects this air store communicates with 
the exposed ones at least along the gap in the region of the meta- 
thoracic epimeron (Figs. 11 and 12, arrow) and quite probably 
along the abdomen as well. It is also possible, however, that either 
or both of these insects contact the atmosphere posteroventrally 
and take air directly into the subalar air store, as does Ambrysus 
(Naucoridae; Parsons 1970). 
Popham (1960) believed that oxygen enters the tracheal system 
of Corixa chiefly through the first abdominal spiracles. This also 
