174 THE ESSEX NATURALIST.
Other bugs of some economic importance are Plesiocoris
rugicollis and Orthotylus marginalis, two very similar green Capsids,
which have spread from their natural food-plants (willows and
sallows) to apple orchards, where they are reported to have done
some harm by sucking the sap and thus weakening the leaves
and fruit.
The life-histories of most of our bugs seem to be very uniform,
so far as known, but there is a vast amount of investigation
required before the life-history of every species can be said
to be even tolerably well-known. Very few of the eggs have
been found, but of those that are known, all are more or less
cylindrical in shape and either self-coloured, or with spots or
bands of other colours. Some are sculptured and others furnished
with filaments, spines and other excrescences. They are deposited
generally in or on the tissues of plants, terrestrial or aquatic,
according to the species. The eggs of the Water-scorpions are
crowned with two or more filaments, those of Nepa resembling a
hydra with retracted tentacles. They are partly embedded in
the stems or leaves of water plants, and oxygen is supplied to
the embryo through the tentacles. The eggs of Aphelochirus
are attached to the shells of molluscs; those of Naucoris and
Notonecta are partly inserted in the stems of water plants. The
eggs of Plea are embedded longitudinally in the stems, whilst
those of Corixa, so far as is known, are attached externally.
The eggs of Ranatra are parasitised by the minute Hymenopteron,
Prestwichia aquatica, which has also been bred from Aphelochirus.
The larvae of the vast majority of the Heteroptera are very
active and roughly resemble the adult in shape, but often differ
considerably in pattern and colour. They can be distinguished
from adults by the entire absence of flying organs and ocelli,
by the tarsi being always two-jointed, and by the orifices of the
stink-glands, when present, being on the dorsal, instead of the
ventral, surface. They undergo several moults, after each of
which the wing-pads become more and more developed, until
in the last instar, or nymph stage (corresponding to the pupal
stage of other orders) these wing-pads are very obvious. It is
interesting that the sheath (i.e., the labium) of the rostrum and
those of the antennae, as well as those of the legs, are all moulted.
As feeding is by suction only, the food must of necessity be
fluid and it consists, therefore, of animal and vegetable juices,