1976] Parsons — Morphology of Corixidae 175 
which form an elaborate “Hagemann’s organ”. The efferent system 
which leads from the metathoracic scent gland is different in Micro- 
necta than in the other two corixids. 
4. In typical Hydrocorisae the first abdominal spiracle lies in the 
posterior part of the metathoracic epimeron. In the three corixids, 
however, it lies in the thoracico-abdominal membrane, and the 
posterior part of the metathoracic epimeron is enlarged into a lobe 
ventral to it. The shape of the lobe differs in the three insects and 
affects the communication between the spiracles and the air stores. 
The lobe is least complex in Diaprepocoris and most complex in 
Hesperocorixa. 
5. In all three corixids the metathoracic spiracle lies in the meso- 
thoracic epimeron and faces directly onto the subalar air store. 
It is smaller than the first abdominal one and, unlike the latter, is 
covered by a “sieve-plate” which appears to limit its porosity. The 
large first abdominal spiracle lacks a sieve-plate and appears to 
be the main site of inhalation in all three insects. It is unmodified 
in Diaprepocoris and Micronecta and is encircled by a trabecular 
collar in Hesperocorixa. 
6. The present investigation supports the views of Popov (1971) 
on the phylogenetic relationships among the three living subfam- 
ilies of Corixidae. 
Explanation of Abbreviations 
The Roman numerals I, II, or III after an abbreviation indicate 
prothoracic, mesothoracic, or metathoracic structures respec- 
tively; an Arabic number following an abbreviation indicates the 
abdominal segment to which the structure belongs. The following 
abbreviations are used: 
AC Antecosta 
AP Abdominal projection 
AT Air trough of metapleuron 
B Base of mesothoracic lateral epimeral lobe 
C Indented portion of metathoracic epimeral lobe 
CA Clavus of forewing 
CL Club-shaped sclerite 
CO Corium of forewing 
