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.