1976] 
Parsons — Morphology of Corixidae 
163 
the latter was clearly observed only in Hesperocorixa (Fig. 28); 
it bears very narrow, slit-like openings which are pinnately arranged 
on an otherwise solid surface. The arrangement of the openings 
is similar to that on the inner membranes of the mesothoracic, 
metathoracic, and eighth abdominal spiracles of Belostoma (Par- 
sons 1972b, 1973). The openings appear, however, to be consid- 
erably narrower, and the metathoracic sieve-plate less porous, in 
Hesperocorixa than in Belostoma. 
The integumental region (Figs. 25-27, IN) lies ventral to the 
sieve-plate. It is definitely at the margin of the plate in Hespero- 
corixa and Micronecta and is either marginal or very acentric 
within the plate in Diaprepocoris. Its size, relative to that of the 
sieve-plate, is largest in Micronecta (Fig. 26) and smallest in Hes- 
perocorixa (Fig. 27). It forms a prominent knob in Micronecta 
and Diaprepocoris (Fig. 25) but is flatter in Hesperocorixa. In all 
three corixids the integumental region is covered with irregular 
folds (Fig. 29) which conceal the position of the ecdysial opening. 
II. First Abdominal Spiracle 
The first abdominal spiracle of all three genera is larger and 
much more permeable than the metathoracic one. Its longest 
dimension, compared with that of the metathoracic spiracle, is 
approximately 135 pm : 90 pm inDiaprepocoris, 45 pm : 35 pm in 
Micronecta, and 320 pm : 275 pm in Hesperocorixa. In Diapre- 
pocoris and Micronecta it lacks a sieve-plate and integumental 
region; the spiracular trachea attaches directly to a round or oval 
opening in the thoracio-abdominal membrane (Figs. 15 and 16, 
S 1) and its orifice is not modified in any way. 
In Hesperocorixa (Fig. 30) the orifice of the spiracular trachea 
lacks an integumental region and is encircled by a collar-like net- 
work of trabeculae which branch and anastomose like those on 
the sieve-plate of the metathoracic spiracle. Unlike the latter, 
however, the trabeculae lack an inner membrane and surround 
the tracheal orifice rather than cover it. The spiracle is thus as 
widely open as its less elaborate homologues in Diaprepocoris and 
Micronecta. The first abdominal spiracle of Hesperocorixa is 
similar to those of Belostoma and Ranatra (Parsons 1972b) except 
that in those two Hydrocorisae the trabeculae cover, rather than 
surround, the tracheal orifice. 
