INSECTA.
and the triangular suture, particularly the ante¬
rior portion, which divides the epicranium
from the clypeus posterior (d), is very distinct.
At the anterior external angle of this part of
the clypeus, as in Coleoptera, are situated the
antenna (a), two short and thick porrected
organs, covered with a few long hairs, and
which, although apparently composed each of
two joints, appear to be rigid and motionless.
Immediately anterior to the clypeus posterior,
and divided from it by a distinct suture, is a
short lunated plate (d*), the clypeus anterior.
The cornua of this part are extended laterally
at the sides of the mouth, and are continuous
with a portion of the under surface of the head
(f) that bounds the labium. Between the two
cornua of the upper surface is extended a strong
and somewhat homy membrane (e), the proper
labrum, which is continuous with a similar
membrane on the under surface (*), the labium,
which thus forms the orifice of the mouth, the
parts of which do not appear to have been
sufficiently examined in this order. Thus,
although the entrance to the mouth is indicated
by a distinctly marked labrum and labium,
scarcely more developed than in Coleoptera,
the habits of the insect require that it should
also be furnished with a strong sucking tube.
Accordingly we find that within this mem¬
branous mouth are situated two curved horny
plates, a little convex on their external, but
concave on their internal surface, and capable
of being protruded to some distance. They are
directed downwards, and when approximated
form a tube analogous to that of Lepidoptera.
These parts have been described by Curtis as
the maxilla (g), of which they seem to be the
proper analogues, so that in the Homaloptera
the maxillæ form the sheath or outer part of the
sucking tube. At the base of these parts,
within the cavity of the mouth, are two horny
margins fringed with dark hairs, which are
probably rudimental maxillary palpi. In the
centre of the mouth is situated an elongated
slender organ (*), which is folded at an angle
like the proboscis of Diptera, but is retractile
within the mouth, and extends backwards to
the entrance to the oesophagus. It consists of
three parts, an inferior one which is strong,
homy, and forms a groove or canal, the upper
surface of which is covered by another smaller
piece, and the two inclose between them a
third setiform organ. Upon the precise nature of
these parts we do not offer a positive opinion ;
the inferior one, which is continuous with the
inflected portion of the labium, seems to repre¬
sent an elongated portion of that organ, and
the middle one probably is the lingua, in which
case the upper one would answer to a similarly
elongated portion of the labrum.
The under surface of the head is divided by
a deep incisure anteriorly, the margins of which
are covered with stiff hairs and form the lateral
boundary of the mouth. The mentum (Z),
described as such by Curtis, is a strong convex
plate, divided also at its anterior part by a con¬
tinuation of the incisure just noticed. The
cornea, (c), of an oval convex shape, are situated
more on the upper than on the lateral part of
907
the head, but the ocelli in this insect are entirely
wanting, unless we regard as a large ocellus
a convex plate situated in the middle of the
most posterior part of the epicranium (b*).
In the other genera of this order, as in Hasmo-
bora, the head is more orbicular and less flat¬
tened; the epicranium is broad and distinct,
and the suture between this part and the
clypeus posterior is strongly marked. In
Melophagus, the tick or sheep-louse, the maxillæ
are of considerable length, and the retractile
portion of the labium inclosing the lingua is of
considerable strength. The ocelli are present, in¬
serted in little excavations in Hamobora, but ab¬
sent in Melophagus. In Nycteribida the head
offers a most anomalous condition of parts, its
form being, as described by Latreille, that of a
reversed cone. We have had no opportu¬
nities of examining for ourselves either the head
or parts of the mouth, which, according to
Messrs. Curtis* and Westwood,f are styliform,
and analogous to those of Hippobosca.
In Aphaniptera the head is compressed
from side to side, but we have not yet identified
its primary parts. Its chief characteristics are
its extreme narrowness, the situation of its
antennae, and the peculiarity of its organs of
vision, the corneæ of the proper eyes being
each simple and not compound as in other
insects. The mouth is formed upon the same
general principles as in the blood-sucking
Diptera, being composed of six primary parts
adapted for piercing the skin, and occasioning
the pain which distinguishes the puncturing of
these troublesome insects.
In Aptera, all of which, like the insects of
the two preceding orders, are parasitic upon
the bodies of other animals, the mouth in one
family, the true Pediculida, is formed for suck¬
ing, but in the other, the Nirmidæ, it is dis¬
tinctly mandibulated, and approaches the usual
type of mandibulated insects.
In Hemiptera the head is often flattened and
somewhat triangular, and the mouth is rostri-
form as in some of the Diptera, but the sheath
of the organ is formed entirely by the labium
(fig. 382, k). The corneæ are usually very
prominent, and are placed at the posterior
angles of the head. The epicranium is distinct,
but its occipital portion is sunk into a notch in
the prothorax. The ocelli are usually two in
number, placed on the most posterior part of
the epicranium, and are constant throughout
the order in the perfect state, but are not deve¬
loped in the larva or pupa. The division of
the head into its primary parts is very distinct
in some genera. In Coreus marginatus the
epicranial suture is strongly marked along the
middle line as far as the space between the
corneæ, where it joins the triangular suture which
passes outwards immediately behind the inser¬
tion of the antennæ, bounding the clypeus
posterior. In some specimens, but more par¬
ticularly in the pupa, a faint longitudinal suture
extends forwards over the clypeus as far as the
* British Entomology, pi. 277.
t On Nycteribia, in Transactions of the Zoologi-
cal Society of London, vol. i. p, 279.