1974 ] 
Parsons & Hewson — Cryphocricos 
523 
plastral devices. The densely-packed hairs on the ventral surfaces of 
the thorax and abdomen strongly resemble those of Aphelocheirus , 
which has plastral respiration (Thorpe and Crisp 1947a) and differ 
from those of Pelocoris, which has “air-bubble” respiration (Parsons 
1974). The microtrichia in the central portions of the fourth 
through sixth abdominal sternites have a shingle-like arrangement 
which strongly resembles that of the plastral devices on the sternites 
of T orridincola (Coleoptera, Hinton 1969b) ; these microtrichia, 
along with the hairs between them, probably also retain a thin layer 
of air. 
The function of the leaf-like setae on the paratergites is more 
problemmatic. They may serve merely to protect the underlying 
plastral hairs from becoming too clogged with debris to allow the 
adherent air layer to carry on gas exchange with the water. Although 
they may, indeed, do this, it is unlikely that it is their sole function, 
since they are absent in other regions with plastral hairs. In Aphelo- 
cheirus, which is also covered with debris, leaf-like setae occur only 
on the second abdominal sense organs, but the experiments of Thorpe 
and Crisp (1947a, 1947b) have shown that the insect is able to 
maintain efficient plastral respiration. 
The presence of large amounts of air among the elongated leaf- 
like setae on the sense organs of Cryphocricos suggests that the 
shorter ones on the rest of the paratergites are similarly capable of 
retaining air, although in smaller and less visible amounts. They 
may well act in conjunction with the underlying plastral hairs, in 
much the same way that long and short hydrofuge hairs hold a 
“macroplastron” external to a “microplastron” in some aquatic Cole- 
optera such as Hydrophilus piceus (Thorpe and Crisp 1949). Like 
the long hairs which retain the “macroplastron” in the latter, the 
leaf-like setae may, under increased hydrostatic pressure, help to 
protect the thin layer of air, which is trapped in the underlying short 
hairs, against water entry. When the insect dives to regions of in- 
creased pressure the posterolateral slope of the setae may increase, 
so that the setae become pressed together and form a barrier against 
water penetration. Their presence only on the paratergites, and their 
absence in other regions, may be connected with the need to protect 
the second through eighth abdominal spiracles, which lie on the sur- 
faces of the paratergites, against flooding. The three more anterior 
pairs of spiracles (mesothoracic, metathoracic, and first abdominal) 
are concealed within invaginations of the exoskeleton and are thus 
more protected than the posterior ones against the entry of water. 
