that arm its mandibles. Of _incisive_ teeth you may find an example
in those that arm the end of the mandibles of most grasshoppers
(_Locusta_), and of the leaf-cutter-bees (_Megachile_ Latr.)[1250];
of the _laniary_ or canine teeth, you will find good examples in
the mandibles of the dragon-flies (_Libellulina_); the two external
teeth of the apex of those of the leaf-cutter bees may be regarded
as between the incisives and laniaries; and the pointed mandibles
without teeth may be deemed as terminating in a laniary one[1251].
The lower part of the inner or concave surface of the mandibles of
grasshoppers will supply you with instances of the _molary_ teeth,
and the apex, also, of those of some weevils, as _Curculio Hancocki_
K.[1252] But the most remarkable example of a molary organ is
exhibited by many of the Lamellicorn beetles, especially those that
feed upon vegetables, whether flower or leaf.--Knoch, who indeed
was the first who proposed calling mandibles according to their
teeth, incisive, laniary, or molary, but who does not explain his
system clearly, observed that the mandibles of some _Melolonthæ_
have a projection with transverse, deep furrows, resembling a file,
for the purpose of bruising the leaves they feed upon[1253]: and
M. Cuvier, long after, observed that the larvæ of the stag-beetle
have towards their base a flat, striated, molary surface; though he
does not appear to have noticed it in any perfect insect[1254]. This
structure, with the exception of the _Scarabæidæ_ and _Cetoniadæ_,
seems to extend very generally through the above tribe; since it may
be traced even in _Geotrupes_, the common dung-chafer, in which at
the base of one mandible is a concave molary surface, and in the
other a convex one, but without any furrows: a circumstance that
often distinguishes those that have furrows.--In the _Dynastidæ_ the
affinity of structure with the _Melolonthidæ_ &c. is more pronounced,
the furrows to which ridges in the other mandible correspond being
reduced to one or two wide and deep ones; whereas in some of the
latter tribe they are very numerous. These mandibles, in many cases,
at their apex are furnished with incisive teeth to cut off their
food, and with miniature mill-stones to grind it[1255]. The part here
alluded to I call the _Mola_.

Were I to ask you what your idea is with regard to the use of
the organs we are considering, you would perhaps reply without
hesitation, "Of what possible use can the _jaws_ of insects be but
to _masticate_ their food?" But in this you would in many instances
be much mistaken; as you will own directly if you only look at
the mandibles of the stag-beetle--these protended and formidable
weapons, as well as those of several other beetles, cannot be thus
employed. "Of what other use, then, can they be?" you will say.
In the particular instance here named, their use, independent of
mastication, has not been satisfactorily ascertained; but in many
other cases it has. Recollect, for instance, what I told you in a
former letter, of those larvæ that use their unguiform mandibles
as instruments of _motion_[1256]. Again: amongst the Hymenopterous
tribes, whose industry and varied economy have so often amused and
interested you, many have no other tools to aid them in their
various labours and mechanical arts: to some they supply the place of
trowels, spades, and pick-axes; to others that of saws, scissors, and
knives--with many other uses that might be named. In fact, with the
insects of this intire Order mastication seems merely a _secondary_,
if it is at any time their use. Still comprehending in one view all
the mandibulate Orders, though some use their mandibles especially
for purposes connected with their economy, yet their most general
and _primary_ use is the division, laceration, and mastication of
their food; and this more exclusively than can be affirmed of the
under-jaws (_maxillæ_). This will appear evident to you, when you
consider that insects in their larva state, in which universally
their primary business is _feeding_, with very few exceptions use the
organs in question for the purpose of mastication, even in tribes, as
the _Lepidoptera_, that have only rudiments of them in their perfect
state--while the _maxillæ_ ordinarily are altogether unapt for such
use. The exceptions I have just alluded to are chiefly confined to
the instance of suctorious mandibles; or those which, being furnished
at the end with an orifice, the animal inserting them into its prey,
imbibes their juices through it. This is the case with the larvæ of
some _Dytisci_, _Hemerobius_, and _Myrmeleon_[1257]; and spiders have
a similar opening in the claw of their mandibles, which is supposed
to instil venom into their prey[1258].

Under this head I must not pass without notice an appendage of the
mandibles, to be found in some of the rove-beetles (_Staphylinidæ_),
as in _Ocypus_, _Staphylinus_, and _Creophilus_ Kirby. In the first
of these it is a curved, narrow, white, subdiaphanous, submembranous,
or rather cartilaginous piece, proceeding from the upper side of the
base of the mandible[1259]; in the second it is broader, straighter,
and fringed internally and at the end with hairs; and in this at
first it wears the appearance of being attached laterally to the
mandible under the tooth[1260], but if closely examined, you will
find that it is separate: in _Creophilus maxillosus_ it is broader.
This is the part I have named _prostheca_. It is perhaps useful in
preventing the food from working out upwards during mastication.

5. _Maxillæ_[1261]. The antagonist organs to the mandible in the
lower side of the head, are the under-jaws, or _maxillæ_--so
denominated by the illustrious Entomologist of Kiel. Linné appears
to have overlooked them, except in the case of his genus _Apis_, in
which he regards them, and properly, as the sheath of the tongue.
De Geer looked upon them in general as part of the apparatus of the
under-lip or _labium_; and such in fact they are, as will appear when
we consider them more particularly. Fabricius has founded his system
for the most part upon these organs, the principal diagnostic of
ten out of his thirteen Classes (properly Orders) being taken from
them; and in the modern, which may be termed the _eclectic_, system,
although the Orders are not founded upon them, yet the characters of
genera, and sometimes of large tribes, are derived from them: and as
they appear less liable to variation than almost any other organ, as
Mr. W. S. MacLeay has judiciously observed, there seems good reason
for employing them--it is therefore of importance that you should be
well acquainted with them.

Their _situation_ is usually below each mandible, on each side of the
_labium;_ towards which they are often somewhat inclined, so that
their tips meet when closed. In some cases, as in the Predaceous
beetles (_Carabus_ L. &c.), they exactly correspond with the
mandibles; but in others their direction with respect to the head is
more longitudinal, as in the _Hymenoptera_, &c. In _substance_ they
may be generally stated to be less hard than those organs; yet in
some instances, as in the _Libellulina_, _Anoplognathidæ_, &c. they
vie with them, and in the _Scarabæidæ_ and _Cetoniadæ_ exceed them,
in hardness. In the bees, and many other _Hymenoptera_, they are
soft and leathery. Their _articulation_ is usually by means of the
hinge on which they sit: it appears entirely ligamentous, and they
are probably attached to the _labium_ at the base, or _mentum_--at
least this is evidently the case with the _Hymenoptera_, in which
the opening of the _maxillæ_ pushes forth the _labium_ and its
apparatus. In that remarkable genus related to the glow-worms, now
called _Phengodes_ (_Lampyris plumosa_ F.), and in the case-worm
flies (_Trichoptera_ K.), the _maxillæ_ appear to be connate with
the _labium_, or at least at their base.--As to their _composition_,
these organs consist of several pieces or portions. At their base
they articulate with a piece more or less triangular, which I call
the hinge (_Cardo_)[1262]. This on its inner side is often elongated
towards the interior of the base of the _labium_, to which it is, as
I have just observed, probably attached. This elongate process of the
hinge in _Apis_, _Bombus_, &c. appears a separate articulation; and
the two together form an angle upon which the _mentum_ sits[1263],
and by this the _maxilla_ acts upon the labial apparatus.

The next piece is the _stipes_ or stalk of the _maxilla_. This is the
part that articulates with the hinge, and may be regarded in some
cases, as in the _Orthoptera_ &c., as the whole of the _maxilla_ below
the feeler; and in others, as in the _Geotrupidæ_, _Staphylinidæ_ &c.,
as only the back of it, the inside forming the lower lobe. This piece
is often harder and more corneous than the terminal part, is linear,
often longitudinally angular, and in the bee-tribes (_Apis_ L.) is
remarkable on its inner side for a series of bristles parallel to each
other like the teeth of a comb[1264]. In _Pogonophorus_ Latr., a kind
of dor or clock-beetle, it is armed on the back with four jointed
spines, the intermediate one being forked[1265]. M. Latreille has thus
described the stipes of the _maxillæ_ of _Coleoptera_: "Next comes
the stalk," says he, "which consists of three parts: one occupies the
back and bears the feeler; the second forms the middle of the anterior
face, and its figure is triangular; the third fills the posterior
space comprised between the two preceding; and is that which is of
most consequence in the use of the _maxilla_; the anterior feeler,
where there are two, the _galea_, and the other appendages that are of
service in deglutition, are part of that piece[1266]."

The _third_ and terminal portion of the _maxilla_ is formed by the
lobe, or lobes (_Lobi_). This may be called the most important part
of the organ, since it is that which often acts upon the food, when
preparing for deglutition. When armed with teeth or spines at the
end, its substance is as hard as that of the mandibles; but when not
so circumstanced, it is usually softer, resembling leather, or even
membrane[1267]; and sometimes the middle part is coriaceous, and the
margin membranous. This part is either simple, consisting only of
_one_ lobe, as you will find to be the case with the _Hymenoptera_,
_Dynastidæ_, _Nemognatha_, and several other beetles; or it is
compound, consisting of _two_ lobes. In the former case, the lobe is
sometimes very long, as in the bee tribes, and the singular genus
of beetles mentioned above[1268], _Nemognatha_; and at others very
short, as in _Hister_, &c. The bilobed _maxillæ_ present several
different types of form. Nearest to those with one lobe are those
whose lower lobe is attached longitudinally to the inner side of
the stalk of the organ, above which it scarcely rises. Of this
description is the _maxilla_ in the common dung-beetle (_Geotrupes
stercorarius_), and rove-beetle (_Staphylinus olens_).[1269]
Another kind of formation is where the lower lobe is only a little
shorter than the upper: this occurs in a kind of chafer (_Macraspis
tetradactyla_ MacLeay).[1270] A third is where the upper lobe covers
the lower as a shield; as you will find in the _Orthoptera_ order,
and the _Libellulina_, and almost in _Meloe_[1271]. A fourth form is
where the upper lobe somewhat resembles the galeate _maxilla_ just
named; but consists of two joints. This exists in _Staphylinidæ_,
&c.[1272] The last kind I shall notice is when the upper lobe not
only consists of two joints, but is cylindrical, and assumes the
aspect of a feeler or _palpus_[1273]. This is the common character
of almost all the Predaceous beetles (_Entomophagi_ Latr.). This
lobe, which has been regarded as an additional feeler, is strictly
analogous to the upper lobe in other insects, and therefore should
rather be denominated a palpiform lobe than a _palpus_. Where there
are two lobes, the upper one is most commonly the longest; but in
many species of the tribe last mentioned the lower one equals or
exceeds it in length[1274].

The lobes vary in form, clothing, and appendages. The upper palpiform
lobe in those beetles just mentioned, in general varies scarcely
at all in _form_; but the genus _Cychrus_ (which is remarkable
for a retrocession from the general type of form of the _Carabi_
L. making an approach towards that of those _Heteromera_ which,
from their black body and revolting aspect, Latreille has named
_Melosomes_,) affords an exception, the upper joint being rather
flat, linear-lanceolate, incurved, and covering the lower lobe[1275],
which it somewhat resembles. The lower lobe also in this tribe
varies as little as the upper, being shaped like the last joint of
that lobe in _Cychrus_ just described, except that in _Cicindela_ it
is narrowest in the middle[1276]. In other tribes the upper valve is
sometimes linear and rounded at the apex, and the lower truncated, as
in _Staphylinus olens_[1277]; sometimes the upper one is truncated or
obtuse, and the lower acute, as in _Trogosita_ and _Parnus_[1278]. In
_Ptinus_, another tribe of beetles, before noticed as injurious to
our museums[1279], the reverse of this takes place, the upper-lobe,
which is the smallest and shortest, being acute, and the lower
truncated[1280]. In _Blaps_ both are acute[1281]. In _Rhipiphorus_
and _Scolytus_ the lobes are nearly obsolete. The lower lobe is bifid
in _Languria_, a North American genus of beetles, so as to give the
maxilla the appearance of three lobes[1282]; and in _Erotylus_,
a South American one, the upper is triangular[1283]: it is often
oblong, quadrangular, linear, &c. in others.--In those that have
only one lobe the shape also varies. In _Gyrinus_, the beetle that
whirls round and round on the surface of every pool, which, though
it belongs to the Predaceous tribe, has only one lobe, the lobe
represents a mandible in shape of the laniary kind, being trigonal
and acute[1284]; and in the _Anoplognathidæ_, a New Holland tribe
of chafers, in which it is, as it were, broken, the lobe forming an
angle with the stalk, it is concavo-convex and obtuse, and somewhat
figures a molary tooth[1285]. In the first tribe into which the bees
(_Apis_ L.) have been divided (_Melitta_ Kirby), the lobe is often
linear or strap-shaped, and bifid at the apex; and in the second
(_Apis_ K.) lanceolate and intire[1286]. In _Cerocoma_ it is long and
narrow[1287]. More variations in form might be named, but these are
sufficient to give you a general idea of them in this respect. With
regard to their _clothing_, I have not much to observe--in examining
the Predaceous beetles you will observe, that the interior margin of
the lower incurved lobe is fringed with stiff bristles or slender
spines, and in many other beetles either one or both lobes have a
thick coating or brush of stiffish hairs[1288]; but in several cases
only the apex of the lobe is hairy. In the _Orthoptera_ order, and
many of the _Melolonthidæ_ or chafers, the whole _maxilla_ is without
hairs, or nearly so.

The _appendages_ of the _maxillæ_ are next to be noticed. These are
principally their claws, or laniary teeth; for they are seldom armed
with incisive or molary teeth. The whole tribe of Predaceous beetles,
with few exceptions, have the inner lobe of their _maxilla_ armed
with a terminal claw, which in the _Cicindelidæ_ articulates with the
lobe, and is moveable, but in the rest of the tribe is fixed[1289].
In _Phoberus_ MacLeay the lower lobe has two spines[1290]. In
_Locusta_ this lobe has three or four spines or laniary teeth, and
in _Æshna_ there are six, which, like the claw of _Cicindela_, are
moveable[1291]. In others both lobes terminate in a single spine or
claw: this is the case with _Paxillus_ MacLeay[1292]. In _Passalus_,
nearly related to the last genus, the upper lobe is armed with a
single spine, and the lower one with two[1293]. Those _maxillæ_
that terminate in a single lobe are also often distinguished by the
spines or teeth with which it is armed; thus in a nondescript chafer
belonging to the _Dynastidæ_ (_Archon_ K. MS.) it terminates in _two_
short teeth; in that remarkable Petalocerous genus _Hexodon_ Oliv.
in _three_ truncated _incisive_ ones[1294]; in _Dynastes Hercules_
in three _acute_ spines[1295]. _Four_ similar ones arm the apex of
the _maxilla_ in that tribe of _Rutelidæ_ which have striated elytra;
and _five_ that are stout and triquetrous those of _Melolontha
Stigma_ F. Many others have _six_ spines, sometimes arranged in a
triple series[1296]. Besides teeth or spines, in some cases the
lobes of _maxillæ_ terminate in several long and slender _laciniæ_
or lappets fringed with hairs. At least those of a _Leptura_
(_L. quadrifasciata_ L.) described by De Geer, appear to be thus
circumstanced. He conjectures that this beetle uses its _maxillæ_ to
collect the honey from the flowers[1297].

As the principal use of the mandibles is cutting and masticating, so
that of the organs we are considering seems to be primarily that of
_holding_ the food and preventing it from falling while the former
are employed upon it. I say this is their _primary_ use; for I
would by no means deny that they assist occasionally in comminuting
or lacerating it. In fact, were there no organs appropriated to
this use, and if both mandibles and _maxillæ_ were employed at
the same time in comminuting the food, it seems to me that it
must fall from the mouth. In a large proportion of insects the
lobes of the _maxillæ_ are not at all calculated for laceration or
comminution; and in those tribes--as the _Melolonthidæ_, _Rutelidæ_,
_Dynastidæ_--in which they seem most fitted for that purpose, the
mandibles have _incisive_ teeth at their apex, and at their base a
powerful _mola_ or grinder: circumstances which prove, that even in
this case the business of mastication principally devolves upon them.

6. _Palpi Maxillares_[1298]. There is one circumstance that
particularly distinguishes the _maxillæ_ from the mandibles--they
are _palpigerous_, as well as the under-lip. The feelers, or palpi,
emerge usually from a sinus observable on the back of the _maxillæ_
where the upper lobe and stalk meet. Their articulation does not
materially differ from that of the labial palpi. Each _maxilla_ has
properly only _one_ feeler; but, as was lately observed[1299], in
certain tribes the upper lobe is jointed and palpiform, which has
occasioned it to be considered as a feeler, and these tribes have
been regarded as having six feelers. The most general rule with
regard to the _length_ of the _palpi_ is, that the maxillary shall
be longer than the labial; but the reverse often takes place. In
many _bees_ the maxillary consist only of a _single_ joint, and
are very _short_; while the labial consist of _four_, and are very
_long_[1300]: and in some insects (as in _Pogonophorus_ Latr.)
the four palpi are of equal length[1301]. The antennæ are most
commonly longer than the palpi; but in several aquatic beetles, as
_Elophorus_, _Hydrophilus_, &c., whose antennæ in the water are not
in use, the organs we are considering are the longest.--As to the
_number_ of their articulations, it varies from one to six; which
number they are not known to exceed. In each of the Orders a kind
of law seems to have been observed as to the number of joints both
in the maxillary and labial palpi, but which admits of several
exceptions. Thus in the _Coleoptera_, the _natural_ number may
be set at _four_ joints for the _maxillary_, and _three_ for the
_labial_ palpi: yet sometimes, as in _Stenus_, _Notoxus_, &c., the
_former_ have only _three_ joints, and the _latter_, as in _Stenus_
and _Tillus_, only _two_. In the _Orthoptera_ the law enjoins _five_
for the _maxillary_, and _three_ for the _labial_; and to this I
have hitherto observed no exception. In the _Hymenoptera_, the rule
is _six_ and _four_, but with considerable exceptions, especially
as to the _maxillary_ palpi, which vary from _six_ joints to a
_single_ one: thus in the hive-bee and the humble-bee, the labials,
including the two flat joints or elevators, have four joints, while
the maxillaries are not jointed at all[1302]. In _Chrysis_, in which
the latter consist of _five_, the former are reduced to _three_. The
_Libellulina_ may almost be regarded as having no maxillary palpi,
since they exhibit no organ that is distinctly palpiform. It seems to
me that the upper lobe of their maxilla, which articulates with the
stalk in the same manner as a feeler, may be regarded as an instance
in which that lobe and the feeler coalesce into one; and the mucro
that proceeds from the lobe has the aspect of an emerging feeler, and
corresponds somewhat with the labial one above noticed[1303]. In the
remainder of the _Neuroptera_ and the _Trichoptera_, the prevailing
number is _five_ and _three_. In the latter there are exceptions,
which will furnish good characters for genera. In the _Lepidoptera_
we find _two_, and sometimes _three_, the maxillary being very
minute[1304]. The _Diptera_ Order presents two tribes in this
respect quite distinct from each other. The most natural number of
joints in the maxillary palpi of the _Tipulidæ_, _Culicidæ_, &c. is
_four_ or _five_: the last joint, however, in _Tipula_, _Ctenocera_,
&c. like that of the antennæ in _Tabanus_ L., appears to consist
of a number of very minute joints[1305]; but in the _Asilidæ_ and
_Muscidæ_, &c., the number _two_ seems to be most prevalent[1306].
The _labial_ palpi in this order are obsolete.--As to _shape_, the
maxillary palpi, as well as the labial, are usually filiform; but in
the weevil tribes (_Curculio_ L.) they are most commonly very short
and conical[1307]; in the chafers (_Scarabæus_ L.) they usually are
thickest at the apex[1308]; in _Megachile_ and _Euglossa_, wild bees,
they are setaceous, growing gradually more slender from the base
to the summit[1309]: a tribe of small water-beetles (_Haliplus_),
the saw-flies (_Tenthredo_ L.), and several other _Hymenoptera_,
have them thickest in the middle[1310]. Their most important part,
however, and that which varies most in form, is the _terminal_
joint:--of this I have already related some singular instances[1311],
and shall now describe a few more. This joint is sometimes acute,
at others blunt, at others truncated: in figure it is ovate,
oblong, obtriangular, hatchet-shaped, lunate, transverse, conical,
mammillate, subulate, branched, chelate, laciniate, lamellate, &c.
&c.[1312]: terms which I shall more fully explain to you hereafter,
and which I only mention here to show the numerous variations as to
figure, of which this joint exhibits examples. The palpi in general
at their vertex are often rather concave; and this concavity is
formed by a thin papillose membrane, which it is supposed the animal
has the power of pushing out a little, so as to apply it to surfaces.
The _primary_ use of the palpi of insects will be considered when I
treat of their senses; but they probably answer more purposes than
one. For instance, when I was once examining, under a lens, the
proceedings of a species of _Mordella_, which was busily employed
in the blossom of some umbelliferous plant, it appeared to me to
open the anthers with its maxillary palpi, and they often held the
anther between them: when not so employed, they were kept in intense
vibration, more than even its antennæ; and at the same time, as far
as I could judge, an _Elater_ made the same use of them.

7. _Lingua_[1313].--This name was applied by Linné to the part in
insects representing the _tongue_ in vertebrate animals; and as it
performs most of the common offices of a tongue, and the _pharynx_
is situated with respect to it, as we shall presently see, nearly
as it is in those animals, there seems no more reason for giving
it a new name, than there is for giving a new name to the head or
legs of insects, because in some respects they differ from those of
the higher animals. I shall not therefore call it _Ligula_, with
Fabricius and Latreille, nor _Labium_, with Cuvier and others, but
adhere to the original term, which every one understands.

The _tongue_ lies between the two _lips_--the _labrum_ and _labium_.
On its upper side, at the base, it meets the palate or roof of the
mouth, below which it is attached, it may be presumed, by its roots
to the crust of the head, on each side the _pharynx_ or swallow; and
on its lower side, in many cases, it is attached to the _labium_, and
that very closely, so as to appear to be merely a part of it, and
to form its extremity: but in the _Orthoptera_ and _Libellulina_,
it is more free, and in form somewhat resembling the tongue of the
quadrupeds[1314].--In _substance_ the tongue varies. In general it
seems something between membrane and cartilage; but in the Predaceous
beetles, in which it is not covered by the _labium_, it approaches
nearer to the substance of the general integument, and in _Anthia_ F.
it is quite hard and horny:--that just mentioned of the _Orthoptera_
and _Libellulina_ is more fleshy[1315]. With regard to its _station_,
in many cases, as in the instance just named, in the Lamellicorn
tribe (_Scarabæus_ L.) and others, it is, when unemployed, concealed
within the mouth; the lips, mandibles, and maxillæ all closing over
it. The tongue of some _Hymenoptera_ also is retractile within the
mouth. "When _ants_ are disposed to drink," says M. P. Huber, "there
comes out from between their lower jaws, which are much shorter
than the upper, a minute, conical, fleshy, yellowish process, which
performs the office of a tongue, being pushed out and drawn in
alternately: it appears to proceed from the lower-lip.--This lip has
the power of moving itself forwards in conjunction with the lower
jaws: and when the insect wishes to lap, all this apparatus moves
forward; so that the tongue, which is very short, does not require to
lengthen itself much to reach the liquid[1316]." M. Lamarck thinks
that the _labium_ of insects has a _vertical_ motion (_de haut en bas
ou de bas en haut_)[1317]. This it certainly has in some degree; but
it has also, as in the above case, a more powerful _horizontal_ one,
which is produced, in _Hymenoptera_ at least, by the opening of the
maxillæ--as I have already observed[1318].

I have little to say with respect to the _structure_ of the tongue:
it generally seems to be without articulations; but in many bees it
articulates with the _labium_ where it enters it, so as when unemployed
to form a fold with it. In the hive-bee it terminates in a kind of
knob or button, which has been falsely supposed to be perforated
for imbibing the honey by suction. The upper part of this tongue
is cartilaginous, and remarkable for a number of transverse rings:
below the middle, it consists of a membrane, longitudinally folded in
inaction, but capable of being inflated to a considerable size: this
membranous bag receives the honey which the tongue, as it were, laps
from the flowers, and conveys it to the _pharynx_[1319]. In _Stenus_
this organ is retractile, and consists of two joints[1320].

The _shape_ of the tongue of insects probably varies as much as
any other part; but as it is apt to shrink when dried[1321],
and is not easy to come at, we know but little of its various
configurations:--in the bees it is very long, in most other insects
very short. Though frequently simple and undivided, in many cases
it presents a different conformation. Thus in the saw-flies
(_Tenthredo_ L.) it terminates in three equal lobes[1322]; in
_Stomis_ and _Geotrupes_ in three unequal ones, the intermediate
being very short[1323]; in _Carabus_, in three short teeth[1324];
in _Pogonophorus_ it represents a trident[1325]; in the wasp it is
bifid, each lobe being tipped with a callosity[1326]; in _Melolontha
Stigma_ it is bipartite[1327]; in _Elaphrus_, the analogue of the
tiger-beetles, it terminates in a single tooth or point; in the
aquatic beetles, _Dytiscus_ L., it is quadrangular and without
teeth[1328]; in some _Ichneumonidæ_ it is concavo-convex, and forms a
demitube; and in others it is nearly cylindrical[1329].

In many insects it has no _hairs_, but in the Predaceous beetles it
generally terminates in a couple of bristles[1330]. In the hive-
humble- and other bees, it is extremely hairy[1331]; a circumstance
which probably enables it more effectually to despoil the flowers of
their nectar. In _Geotrupes stercorarius_, the common dungchafer, and
_Melolontha Stigma_ lately mentioned, the lobes of the tongue are
fringed with incurved hairs[1332]; and in _Æshna_ it is hairy on the
upper side, each hair or bristle crowning a minute tubercle. In many
cases the tongue is attended, and sometimes sheathed at the base,
by two usually membranous appendages:--these the learned Illiger
has denominated _paraglossæ_; and I shall adopt his term. You
will find them frequently attached to the tongue of the Predaceous
beetles[1333], and to that of many _Hymenoptera_. In the hive-bee and
humble-bee they are short, and take their origin within the _labial_
feelers[1334]: in _Euglossa_, another bee, they are long, involute at
the tips, and, what is not usual with them, very hairy[1335]: in the
wasp, like the lobes of the tongue, they are tipped with a callosity.

Under this head I may observe to you, that the insects whose oral
organs we are considering besides a _tongue_ appear likewise to be
furnished with a _palate_ (_Palatum_). This, though a part of the
roof of the mouth, is not precisely in the situation of the palate
of vertebrate animals, since it seems rather the internal lining of
the _labrum_. If you take the common dragon-fly (_Æshna viatica_),
you will find that the under side of this part and of the _rhinarium_
is lined with a quadrangular fleshy cushion, beset, like the upper
surface of the tongue, with minute black tubercles, crowned with
a bristle. This cushion is divided transversely into two parts by
a depression; the anterior or outer piece being attached to the
_labrum_, and the other piece to the _rhinarium_. The former has a
central longitudinal cavity, black at the bottom, on the sides of
which the tubercles are flat and without a bristle. From its base on
each side a spiniform process emerges, forming a right angle with it.
These processes seem the antagonists of those mentioned above[1336],
that emerge from the _labium_. The posterior or inner piece has on
each side a roundish space, attached to the under surface of the two
sides of the _rhinarium_, beset also with bristle-bearing tubercles.
You will find something similar lining the _labrum_ and _nasus_ of
some _Coleoptera_,--say _Geotrupes_, _Necrophorus_, and _Dytiscus_.
The first piece I regard as the analogue of the palate, and the
second as connected with the sense of _smelling_. In _Necrophorus_
the circular pieces are covered with a finely striated membrane, and
in _Dytiscus_ each has a little nipple.

8. _Pharynx_[1337].--On the upper side of the tongue, usually at its
base or root, is the _pharynx_, or aperture by which the food passes
from the mouth to the _œsophagus_. This orifice, which is situated
with respect to the tongue of the _Orthoptera_ and _Libellulina_
nearly as in those insects (at least as far as I have been able to
examine them), whose tongue is called a _ligula_ or _labium_,--of
course exists in all the mandibulate Orders whose mouth we are now
considering. In the _Hymenoptera_ it is covered by a valve, the
_Epipharynx_ of Savigny; and it appeared to me to be so likewise in
one of the _Harpalidæ_ that I examined. The formation seems different
in _Geotrupes_, as far as I can get an idea of it; but it is so
difficult to examine the interior of the mouth without laceration of
some of the parts, that I can only tell you what the appearances were
in one instance, upon removing the _labrum_ from the _mandibles_; and
in another, separating the whole apparatus of the _labium_, including
the _maxillæ_, from the _mandibles_ and _labrum_. In the former case,
the mandibles coincided at the base, the two molary plates (_molæ_),
which in this genus are narrow, transverse and not furrowed, are
so applied as evidently to have an action upon each other, as the
mandible opens and shuts, proper for trituration. Within these is
the base of the tongue, under the form of a ventricose sack. The
upper part of this last organ, which forms the internal covering
of the labium, appears to consist of three (in the recent insect
_fleshy_) lobes, the middle one being bent downwards internally, so
as to form a kind of sloping cover to an orifice in the part I call
the base. After two or three days, the tongue shrinks and dries to
a hard substance;--between the mandibles and the base of the tongue
I could not discover the _pharynx_. The above apparent opening
covered by the tongue was the only one I could perceive. In the
latter case, the form and structure of the base of the tongue is more
visible: it is an oblong ventricose tubular sack, projecting above
anteriorly into an acute angle formed by a fine white membrane, most
beautifully and delicately striated with oblique striæ, to be seen
only under a powerful lens: on the anterior side of this sack are
two parallel cartilaginous ridges close to each other, fringed with
short hairs, which take their origin from the angle. I could not be
certain whether the orifice covered by the intermediate lobe was only
apparent, or real; but I did not succeed in my endeavour to find any
other _pharynx_, though from the molary structure of the base of the
mandibles one may conjecture that there must be one situated at the
base of this sack to receive the food they render after trituration.
The excrement of this animal is not fluid. In the _Libellulina_
the _pharynx_ seems closed by two valves meeting. This part in
_Hymenoptera_, and probably in other Orders, has the aspect of being
cartilaginous and fitted to sustain the action of the substances that
have to pass through it[1338].

The _Epipharynx_ is a valve, called by M. Latreille _sublabrum_
(_sous labre_[1339]), attached by its base to the upper margin of
the _pharynx_, or that next the _labrum_. In the bees it is said by
Reaumur to be of a fleshy substance, and capable of changing its
figure. He seems to think it the real _tongue_ of the bee[1340]; but
as it does not appear to have any of the uses of a tongue, and merely
closes the orifice of the mouth, it surely does not merit that name.
M. Savigny calls it a membranous appendage which exactly closes the
_pharynx_[1341]. De Geer has examined the _epipharynx_ of the wasp,
which he describes as of a scaly substance, and regards merely as the
cover of the part just named[1342].

With regard to the _Hypopharynx_, which Latreille considers as a
support and appendage of the _epipharynx_, I have little to add to
the definition I have given of it above. In the _Libellulina_ the
base of the tongue terminates towards the _pharynx_ in a fleshy
cushion, armed at each angle next to that part with a short hard
horn or tooth of a black colour. This cushion, I suppose, may be
analogous to the _hypopharynx_ of M. Savigny[1343]. On the opposite
side the pharynx is closed by another fleshy cushion (_epipharynx?_),
which appears to line the nose, behind those two mammillæ before
described[1344], which form the internal covering of the _rhinarium_.

Before I call your attention to what I would denominate an
_imperfect mouth_, in which some one or more of the seven organs
above enumerated exist under another form, or only as rudiments,--I
must say something upon the mouth of the _Myriapods_ and _Arachnida_,
in which there seem to be _redundant_ organs of manducation.--M.
Latreille, in the Essay lately quoted, in which, though some of
his notions seem fanciful, he has shown a vast depth and range of
thought and research, has asserted,--from the admirable and curious
observations of M. Savigny, and those which since their publication
he has made himself,--that the masticating organs of _annulose_
animals (called by him _condylopes_) are a kind of _legs_[1345].
And M. Savigny, whose indefatigable labours and unparalleled
acuteness have opened the door to a new and vast field in what may
be denominated analogical anatomy,--has observed, that with certain
_Apiropods_[1346] the organs that serve for manducation do not differ
essentially from those which, with the other _Apiropods_ and the
_Hexapods_, serve for _locomotion_[1347]: and the unguiform mandibles
of the larvæ of certain _Diptera_, you have before been told, are
used not only in manducation, but also as legs[1348]. These remarks
will satisfactorily prove to you, that organs which at first sight
possess no visible affinity or analogy--as for instance, jaws and
legs--may, if traced through a long series of beings, exhibit a very
great one;--and will lessen your surprise when you find, that in
certain tribes such commutations of organs and their use take place.

The following is the structure, as to its organs, of the mouth of
the myriapods, as exhibited by the centipedes (_Scolopendridæ_). The
part which appears to perform the office of the upper lip (but which
M. Savigny regards as the nose, calling it the _chaperon_,) is a
transverse piece with a deep anterior sinus, in the centre of which is
a minute tooth[1349]. This piece is separated from the forepart of the
head by a suture; but it probably is not moveable: however, it covers
the mouth, and may be regarded rather as analogous to the _labrum_.
Below this are two mandibles, armed at their end with five sharp
triangular teeth[1350], under which are the _maxillæ_, terminating
in a moveable concavo-convex lobe, resembling the valve of a bivalve
shell[1351]; and between them is the _labium_, of a rhomboidal shape,
divisible into two lobes, attached laterally to the maxillæ: these
lobes M. Savigny terms the _second maxillæ_, forming with the others,
according to him, the _labium_[1352]. Affixed to the base of this
labium, or covering it on the outside, are a pair of pediform palpi,
which he considers as the first auxiliary _labium_, and representative
of the first pair of legs of hexapods and _Iuli_[1353]. I imagine them
to be also the analogues, in some degree, of the labial palpi of a
perfect mouth. The last of the organs in question is a large rhomboidal
plate affixed to the first apparent segment of the trunk, crowned at
its vertex with two truncated denticulated teeth, and from the upper
sides of which emerge a pair of moveable organs terminating in a
powerful incurved claw, and which entirely covers all the other parts
of the mouth[1354]. This, M. Savigny deems as a _second_ auxiliary
_labium_, and the lateral organs of prehension,--which may be regarded
each as a kind of maxillary hand, and as the only representatives in
this tribe of the maxillary palpi, though widely different,--he looks
upon as really analogous to the _second_ pair of legs in _Iulus_
and the hexapods[1355]. These two pairs of pedipalpes (to use an
expressive French term) show their relation to legs by their general
structure, and their analogy with palpi by their use as _oral_ organs,
though belonging to the _trunk_: so that here we see the _legs_ and
their appendages assume a material function in _manducation_, forming
a singular contrast to what we had observed before with regard to
_mandibles_ becoming instruments of _locomotion_. The mouth of the
_Iulidæ_, with little variation, is upon the same plan[1356] with those
here described.

The next type of form with regard to the oral organs is that of the
_Arachnida_. In these, as you know, the head is confounded with the
trunk; so that they are a kind of Blemmyes in the insect world. Their
organs of manducation, amongst which there is no _labrum_ or upper lip,
are, in the first place, a pair of mandibles planted close and parallel
to each other in the anterior part of the head, which they terminate.
In the spiders they consist of two tubular joints, of which the first
is much the largest, more or less conical or cylindrical, and armed
underneath with a double row of stout teeth; and the terminal one is
more solid and harder, in the form of a very sharp crooked claw, which
in inaction is folded on the first joint between the teeth. Under its
extremity on the outside is a minute orifice, destined to transmit a
venomous fluid, which is conducted there by an internal canal from
the base of the first joint, where is the poison-bag[1357]. In the
scorpion and harvest-man (_Phalangium_) the mandible consists of two
joints terminated by a _chela_ or double claw, the exterior one being
moveable[1358].--M. Latreille, as has been before observed, regards
these not as representatives of the mandibles of hexapods, but as
replacing the interior pair of antennæ, in the situation of which they
are precisely placed, of the _Crustacea_[1359]: and M. Savigny is of
opinion that the _Arachnida_ may in some sort be defined as _Crustacea_
without a head, and with twelve legs, of which the two first pair are
converted into _mandibles_ and _maxillæ_[1360]. From the _situation_ of
the organs in question, the first of these opinions seems preferable;
but the conversion of the legs in other cases, at least the _coxæ_,
into organs of manducation, gives some weight to the last. With regard
to their _use_, it is said to be to retain the insect which the animal
has seized, and to facilitate the compression which the maxillæ
exercise upon it for the extraction of the nutritive matter[1361].
If this be correct, _in this respect_ the mandibles may be said to
represent the _maxillæ_ of the mandibulate hexapods; and, _vice versa_,
the _sciatic_ maxillæ, as they have been denominated[1362], of the
_Arachnida_, their mandibles. The palpi are pediform, and the first
joint of the _coxa_, or hip, acts the part of a _maxilla_:--this is
composed of a single piece or plate, more or less oval or triangular,
sometimes straight and sometimes inclined to the _labium_, with
the interior extremity very hairy. The _labium_ consists also of a
single piece, and is only an appendage of the anterior extremity of
the breast. The interior of the mouth, or palate, presents a fleshy,
hairy, linguiform piece, which is usually applied to the internal face
of the _labium_. An opening is supposed to exist in its sides, for
the transmission of the alimentary juices[1363]. If you examine the
under side of the body of a scorpion, you will find that not only the
palpi, but the two anterior pair of legs, by means of their _coxæ_, are
concerned in manducation: so that these insects have in fact _three_
pairs of maxillæ--a circumstance that M. Savigny has observed to take
place also in the harvest-men (_Phalangium_ L.)[1364]. The _palpi_ of
the scorpion, which may be called its _hands_, like the anterior legs
of the lobster and crab, terminate in a tremendous _chela_ or forceps,
consisting of a large triangular joint, armed at the end with a double
claw internally toothed; the _exterior_ one of which, contrary to
what takes place in the animals just named, is moveable, and not the
_interior_[1365].

Having given you this full account of the _trophi_ of those animals
that have all the organs of manducation developed, I must next advert
to those in which one part receives an increment at the expense of
others, and the whole oral machine is fitted for _suction_; or where
some parts appear to be deficient, so that this may be called an
_imperfect_ mouth. At first sight one would regard the trophi of a
_bee_ as of this description; but this is not the case, since it has
all the ordinary organs, though the tongue is unusually long, and
looks as if it was made for suction; which, however, as you have been
informed, is not the case.

There are _five_ kinds of _imperfect_ mouth to be met with in insects
that take their food by suction, each of which I shall distinguish
by a separate denomination. The first is that of the _Hemiptera_
Order:--this I term the _Promuscis_; the second is that of the
_Diptera_, which with Linné I call _Proboscis_; the third, peculiar
to the _Lepidoptera_, is with me an _Antlia_; the fourth, which I
name _Rostrulum_, is confined to the _Aphaniptera_ order, or genus
_Pulex_ L.; and the last is _Rostellum_, which I employ to denote the
suctory organs of the louse tribe (_Pediculidæ_).

i. _Promuscis_[1366].--The organ we are first to consider has usually
been denominated _Rostrum_: but since that term is likewise in
general use for the snout of insects of the weevil tribes (_Curculio_
L.), I think you will concur with me in adopting the one here
proposed, for the very different oral instruments of the _Hemiptera_.
Illiger has employed _promuscis_ to denote those of _bees_[1367]:
but since, as I have just observed, they consist of all the ordinary
organs, they seem to require no separate denomination: the term,
therefore, may be applied to represent a different set of _trophi_,
without any risk of producing confusion. This part consists of
_five_ pieces: viz. a minute, long, conical piece, commonly very
slender, which covers the base of the _promuscis_, and represents the
_labrum_[1368]; a jointed sheath (_vagina_), consisting of either
three or four joints, the analogue of the _labium_, and four slender
rigid lancets (_scalpella_), the two exterior ones, according to M.
Savigny, representing the _mandibles_, and the intermediate pair
the _maxillæ_[1369]. By the union of these four pieces a suctorious
tube is formed, which the animal inserts into the substance, whether
animal or vegetable, the juices of which form its nutriment. These
pieces are dilated at their base, and serrated at their apex; and the
two central ones, though at their origin they are asunder, form one
tube, which has often been mistaken for a single piece. A _pharynx_
and _tongue_ have been discovered by M. Savigny in this apparatus;
who thinks that in _Nepa_ there are also rudiments, but very
indistinct, of _labial palpi_: so that the _maxillary palpi_ seem to
be the only part absolutely wanting[1370].

The _Promuscis_ when at rest is usually laid between the legs; but
when employed, in most cases its direction is outward. In the genus
_Chermes_ L. (_Psylla_ Latr.) the origin of the _promuscis_ has
been supposed to be in the _breast_; but if closely examined, this
anomaly in nature will be found not to exist. If you take one of
these insects, the first thing that strikes you upon inspecting the
head, is a pair of remarkable conical processes into which the front
appears to be divided. Look below these, and you will there discover
the upper-lip: and from this you may follow the _promuscis_ till it
gets beyond the forelegs, when it takes a direction perpendicular
to the body[1371]; a circumstance which has given rise to the above
false notion. Though in _Coccus_, _Chermes_, &c. this instrument is
short, in some _Aphides_ it is longer in proportion than in any other
insect. In _A. Quercus_ it is three times the length of the body; so
that when folded, it stretches out beyond it, and looks like a long
tail[1372]; and in _A. Abietis_ it even exceeds that length[1373].

ii. _Proboscis_[1374].--Linné long since, and after him Fabricius,
has employed this term to designate the oral instruments, or rather
their sheath, in the _Muscidæ_ and some others, calling the same
organ, when without fleshy lips, _rostrum_ and _haustellum_: but
as the parts of the mouth in all true _Diptera_ (for _Hippobosca_
and its affinities can scarcely be deemed as co-ordinate with the
rest), are analogous to each other; although in some they are stiff
and rigid, in others flexile and soft, and in _Œstrus_ (except the
palpi) mere rudiments,--the same appellation ought to designate them
all. I am happy to find that M. Latreille agrees with me in this
opinion; and to his sensible observations on this head, if you wish
for further information, I refer you[1375]. The mouth of Dipterous
insects appears to vary in the number of pieces that it presents;
but in all, the _theca_ or sheath is present, which represents the
_labium_ (including the _mentum_) of the mandibulate Orders[1376].
It consists of _three_ joints, the last of which is formed by the
liplets (_Labella_). Those in the _Muscidæ_ are large, turgid,
vesiculose, and capable of dilatation; in the _Bombylidæ_ and other
tribes they are small, slender, long and leathery, and sometimes
recurved. The second joint or stalk, which may be said to represent
the _mentum_, the liplets being properly in a restricted sense
the analogue of the _labium_, its sides being turned up, forms a
longitudinal cavity, which contains the _haustellum_. The upper piece
of this, the _valvula_, is long, rigid, and very sharp, representing
the _labrum_[1377]. Beneath this cover, in the above cavity, are the
lancets; which, as far as they are at present known, vary in number
and form: sometimes there are _five_ of them, sometimes _four_,
sometimes _two_, and sometimes, it should seem, only _one_[1378]. In
the gnat (_Culex_) they are finer than a hair, very sharp, and barbed
occasionally on one side[1379]; in the horse-fly (_Tabanus_ L.) they
are flat and sharp like the blade of a knife or lancet[1380]. In
this tribe the upper pair, or the knives (_Cultelli_), represent the
_mandibles_; the lower pair, or the lancets (_Scalpella_), usually
palpigerous, the _maxillæ_; and the central one the _tongue_. In the
horse-fly Reaumur has figured only _four_, exclusive of the _labrum_
and _labium_; but in a specimen I have preserved there appear to be
_five_, one of which, as slender as a hair, I regard as the analogue
of the tongue[1381].--When the lancets are reduced to two, they
probably represent the _maxillæ_, the mandibles being absorbed in the
_labrum_; and where there is only one, the maxillæ also are absorbed
by the _labium_, which then bears the palpi, the lancet representing
the tongue[1382]. The lancets are so constructed in many cases, as
to be able by their union to form a tube proper for suction, or
rather for forcing the fluid by the pressure of the lower parts to
the _pharynx_[1383]. _Labial palpi_ appear not usually present in the
_proboscis_; but M. Savigny thinks he has discovered vestiges of them
in _Tabanus_[1384]. In this genus the maxillary ones are large, and
consist of _two_ joints[1385]. The proboscis is often so folded, as
to form two elbows; the base forming an angle with the stalk, and the
latter with the lips, so as in shape to represent the letter Z, only
that the upper angle points to the breast, and the lower one to the
mouth: this is the case with the flesh-fly and many others. In other
flies, as _Conops_ and _Stomoxys_, whose punctures on our legs so
torment us[1386], there is only a single fold, with its angle to the
breast. The _proboscis_ is received in a large oblong cavity of the
underside of the anterior part of the head.

It may here be observed, that in the _promuscis_ the elongation
of the organs seems to be made chiefly at the expense of _all_ the
palpi, but in the _proboscis_ at that of the _labial_ only; and in
some cases at that also of the _mandibles_ or _maxillæ_;--the former
merging in the _labrum_ and the latter in the _labium_.

iii. _Antlia_[1387].--The _third_ kind of imperfect mouth is that
of the _Lepidoptera_, which I have called _Antlia_. Fabricius
denominates it _lingua_: but as this organ has no analogy with the
real tongue of insects, this is confessedly improper, and it appeared
necessary therefore to exchange it for another denomination: I
have endeavoured to apply a term to it that indicates its use--to
pump up, namely, the nectar of the flowers into the mouth of the
insect. On a former occasion I described to you the structure of
this instrument[1388]; but further discoveries with regard to it
having since been made by MM. Savigny and Latreille, I shall here
give you the result of their observations. The former of these
able physiologists has detected in the mouth of the _Lepidoptera_
rudiments of almost all the parts of a perfect mouth. Of the
correctness of this assertion you may satisfy yourself, if you
consult his admirable elucidatory plates, and compare them with the
insects. Just above the origin of the spiral tongue or pump, the head
is a little prominent and rounded; and immediately below the middle
of this prominence there is a very minute, membranous, triangular or
semicircular piece; which from its position, as covering the base of
the _antlia_, may be regarded as the rudiment of the _upper-lip_
(_labrum_)[1389]. On each side of the outer base of the _antlia_ is
another small immoveable piece, resembling a flattened tubercle,
the end of which is internally hairy or scaly: these pieces appear
to represent the _mandibles_[1390]. Near the base of each half
of the _antlia_, just below a sinus, may be distinctly seen the
minute, usually biarticulate rudiment of a _maxillary palpus_[1391];
demonstrating to a certainty that these spiral organs, at least their
lateral tubes or _Solenaria_, are real maxillæ[1392]. The rudiment
of the _under-lip_ (_Labium_) is the almost horny triangular piece
united by membrane to the two stalks of the maxillæ, and supporting
at its base the recurved labial palpi; which are so well known
that I need not enlarge upon them[1393]. Amongst these parts there
seems at first sight no representative of the _tongue_; but M.
Latreille has advanced some very ingenious, and I think satisfactory
arguments[1394], which go to prove that this part, at least the
tongue of _Hymenoptera_, has its analogue in the intermediate tube or
_Fistula_ formed by the union of the two maxillæ, and which conveys
the fluid aliment of this Order to the _pharynx_. As in _Diptera_
the _maxillæ_ sometimes merge in the _labium_, so here the _tongue_
(as it were divided longitudinally) merges in the _maxillæ_. He
further observes, that in a transverse section of the maxilla of the
death's-head hawk-moth (_Sphinx Atropos_), the lateral tube appeared
to be divided into two by a membranous partition, and to contain
in the upper cavity a small cylindrical tube, which seemed to be a
_trachea_[1395]. To animals that are without lungs, and breathe by
_tracheæ_, suction must be performed in a very different way from
what it is by those that breathe by the _mouth_: and as in the very
extended organs in question the fluid has a long space to pass before
it reaches the _pharynx_, in some way or other these lateral tubes
may have the power of producing a vacuum in the middle tube, and so
facilitate its passage thither. We see, in the _antlia_, that the
maxillæ receive their vast elongation at the expense of all the other
organs, except the _labial palpi_.

iv. _Rostrulum_[1396].--An animal very annoying to us affords the
type of the next kind of imperfect mouth--I mean the _flea_. Its oral
apparatus, which I would name _rostrulum_, appears to consist of
_seven_ pieces. First are a pair of triangular organs, the _laminæ_,
which together somewhat resemble the beak of a bird, and are affixed,
one on each side of the mouth, under the antennæ: these represent
the _mandibles_ of a perfect mouth[1397]. Next, a pair of long sharp
lancets (_Scalpella_), which emerge from the head below the laminæ:
these are analogous to _maxillæ_[1398]: a pair of palpi, consisting
of four joints, are attached to these near their base[1399], which
of course are _maxillary palpi_. And lastly, in the midst of all is
a slender setiform organ (_ligula_), which is the counterpart of
the _tongue_[1400]. Rösel, and after him Latreille, seem to have
overlooked this last piece, since they reckon only _six_ pieces
in the flea's mouth[1401]: but the hand and eye of our friend
Curtis have detected a _seventh_, as you see in his figure. From
this account it appears, that the elongation of the organs of the
_Aphaniptera_ Order is at the expense of the _labium_ and its _palpi_.

v. _Rostellum._--So little is known of the composition of the next
kind of imperfect mouth, that I need not enlarge upon it. It is
peculiar to the louse tribe (_Pediculidæ_), and it consists of the
tubulet (_Tubulus_), and siphuncle (_Siphunculus_). The former is
slenderer in the middle than at the base and apex, the latter being
turgid, rather spherical, and armed with claws which probably lay
hold of the skin while the animal is engaged in suction. When not
used, the whole machine is withdrawn within the head; the siphuncle,
which is the suctorious part, being first retracted within the
tubulet, in the same way as a snail retracts its _tentacula_[1402].
This apparatus seems formed at the expense of all the other organs.

There are some other kinds of imperfect mouth, which, though they
seem not to merit each a distinct denomination, should not be passed
altogether without notice. The first I shall mention is that of the
family of _Pupipara_ Latr. (_Hippobosca_ L.). It consists of a pair
of hairy coriaceous valves, which include a very slender rigid tube
or siphuncle, the instrument of suction, which Latreille describes as
formed by the union of two setiform pieces[1403]. In _Melophagus_,
the sheep-louse, the union of the valves of the sheath is so short,
that they appear like a tube; but if cut off they will separate,
and show the siphuncle, as fine as a hair, between them. This organ
is of a type so dissimilar, as was before observed, to that of the
_Diptera_ in general, and approaches so near to that of the dog-tick
(_Ixodes_), that they may be deemed rather apterous insects with two
wings, than to belong to that Order; and the circumstance that some
of the family are apterous confirms this idea. In fact they are a
_transition_ family that connects the two Orders, but are nearest to
the _Aptera_. In _Nycteribia_ the oral organs differ from those of
the other _Pupipara_ in having _palpi_. This also is the case with
those of the genus _Ixodes_, the palpi of which are placed upon the
same base with the instrument of suction, than which they are longer:
they appear to consist of _two_ joints, the last very long and flat.
The instrument of suction itself is formed by three hard rigid
laminæ; two shorter parallel ones above, that cover the third, which
is longer and broader, and armed on each side with several teeth
like a saw, having their points towards the base[1404]. Many of the
other _Acari_ L. have mandibles, and several have not: but their oral
organs have not yet been sufficiently examined; and from the extreme
minuteness of most of them, this is no easy task; nor to ascertain in
what points they differ or agree.

If you consider the general plan of the organs of manducation in the
vertebrate animals, how few are the variations that it admits! An
upper and a lower jaw planted with teeth, or a beak consisting of an
upper or a lower mandible with a central tongue, form its principal
features. But in the little world of insects, how wonderful and
infinite is the diversity which, as you see, in this respect they
exhibit! Consider the number of the organs, the varying forms of
each in the different tribes, adjusted for nice variations in their
uses:--how gradual, too, the transition from one to another! how one
set of instruments is adapted to prepare the food for deglutition by
mastication; another merely to lacerate it, so that its juices can
be expressed; a third to lap a fluid aliment; a fourth to imbibe it
by suction--and you will see and acknowledge in all the hand of an
almighty and all-bountiful CREATOR, and glorify his wisdom, power,
and goodness, so conspicuously manifested in the structure of the
meanest of his creatures. You will see also, that all things are
created after a pre-conceived plan; in which there is a regular and
measured transition from one form to another, not only with respect
to beings themselves, but also to their organs--no new organ being
produced without a gradual approach to it; so that scarcely any
change takes place that is violent and unexpected, and for which the
way is not prepared by intermediate gradations. And when you further
consider, that every being, with its every organ, is exactly fitted
for its functions; and that every being has an office assigned, upon
the due execution of which the welfare, in certain respects, of this
whole system depends, you will clearly perceive that this whole plan,
intire in all its parts, must have been coeval with the Creation; and
that all the species,--subject to those variations only that climate
and different food produce,--have remained essentially the same, or
they would not have answered the end for which they were made, from
that time to this.

Having given you this particular account of the _trophi_ or organs
of the mouth of insects, I must now make some observations upon the
_other_ parts of the head. I have divided it, as you see in the
Table, into _face_ and _subface_; the former including its _upper_
and the latter its _lower_ surface. Strictly speaking, some parts of
the face, as the temples and cheeks, are common to both surfaces; but
I do not therefore reckon them as belonging to the subface, which,
exclusive of the mouth and its organs, consists only of the _throat_,
and where there is a neck, the _gula_.

i. _Nasus_[1405].--I shall consider the parts of the face in the
order in which they stand in the Table, beginning with the _nasus_
or nose. Fabricius has denominated this part the _clypeus_, in which
he has been followed by most modern Entomologists. You may therefore
think, perhaps, that I have here unnecessarily altered a term so
generally adopted, and expect that I assign some sufficient reasons
for such a change. I have before hinted that there is good ground
for thinking that the sense of _smell_ in insects resides somewhere
in the vicinity of this part; and when I come to treat of their
senses, I shall produce at large those arguments that have induced
me to adopt this opinion: and if I can make out this satisfactorily,
you will readily allow the propriety of the denomination. I shall
here only state those _secondary_ reasons for the term, which, in
my idea, prove that it is much more to the purpose than _clypeus_.
This last word was originally applied by Linné in a metaphorical
sense to the ample covering of the head of the _Scarabæidæ_, and the
thoracic shield of _Silpha_, _Cassida_, _Lampyris_, and _Blatta_: in
all which cases there was a propriety in the figurative use of it,
because of the resemblance of the parts so illustrated to a _shield_.
But when _Fabricius_ (though he sometimes employs the term, as Linné
did, merely for illustration,) admitted it into his orismological
table, as a term to represent universally the anterior part of the
face of insects to which the labrum is attached (though in some
cases he designates the _labrum_ itself by this name), it became
extremely inappropriate; since in every case, except that of the
_Scarabæidæ_, the part has no pretension to be called a _shield_;--so
that the term is rather calculated to mislead than illustrate. This
impropriety seems at length to have struck M. Latreille, since in a
late essay[1406] he has changed the name of this part to _Epistomis_,
a term signifying _the part above the mouth_. But there are reasons,
exclusive of those hereafter to be produced concerning the sense of
smell, which seem to me to prove that _nasus_ is a preferable term;
not to mention its claim of priority, as having been used to signify
this part a century ago[1407]. When we come to consider the terms for
the other parts of the head, as _lips_, _jaws_, _tongue_, _eyes_,
_temples_, _cheeks_, _forehead_, &c. the concinnity, if I may so
speak, and harmony of our technical language, seem to require that
the part analogous in point of situation to the _nose_ of vertebrate
animals should bear the same name. And any person who had never
examined an insect before, if asked to point out the _nose_ of the
animal, would immediately cast his eye upon this part: so that one
of the principal uses of imposing names upon parts--that they might
be more readily known--would be attained. If it is objected, that
calling a part a _nose_ that has not the sense of smell, supposing it
to be so, might lead to mistakes--I would answer, that this objection
is not regarded as valid in other cases: for instance, the _maxillæ_
are not generally used as _jaws_, and yet no one objects to the term;
because, from their situation, they evidently have an analogy to the
organs whose name they bear. But enough on this subject--we will now
consider the part itself.

To enable you to distinguish the nose of insects when it is not
separated from the rest of the face by an impressed line, you must
observe that it is the terminal middle part that sometimes overhangs
the upper-lip, and at others is nearly in the same line with it; that
on each side of it are the cheeks, which run from the anterior half
of the eyes to the base of the mandibles. Just below the antennæ is
sometimes another part distinct from the nose, which I shall soon have
to mention; so that the nose must not be regarded as reaching always
nearly to the base or insertion of the antennæ, since it sometimes
occupies only half the space between them and the upper-lip, which
space is marked out by an impressed line. But you will not always be
left at such uncertainty when you want to ascertain the limits of
the nose; for it is in many cases a distinct piece, separated by an
elevated or impressed line from the rest of the face. This separation
is either partial or universal. Take any species of the genera
_Copris_, _Onitis_, or _Ateuchus_, and you will see the nose marked
out in the centre of the anterior part of the face by two _elevated_
lines, forming nearly a triangle and bounded by the horn[1408]. Or
take a common wasp or hornet, and you will find a similar space,
though approaching to a quadrangular figure, marked out by _impressed_
lines[1409]. In _Rhagio_ and _Sciara_, two Dipterous genera, this
impression is so deep as to look like a suture. Between these lines,
in those cases, is included what I call the _nose_. As to _substance_,
in general it does not differ from the rest of the head; but in the
_Cleridæ_ it is almost membranous. You must observe, that in all these,
what at first sight appears to be the termination of the front, is not
the nose, but the narrow depressed piece that intervenes between it
and the lip. With regard to its _clothing_, it is most commonly naked,
but in some genera it is covered with hair; in _Crabro_ F. often with
golden or silver pile, which imparts a singular brilliance to the mouth
of the insects of that genus: M. Latreille supposes that the brilliant
colours of the golden-wasp (_Chrysis_ L.) may dazzle their enemies,
and so _promote_ their escape[1410]; the brilliance of the mouth of
the _Crabro_ may on the contrary at first dazzle their prey for a
moment, so as to _prevent_ their escape. The _form_ of the nose, where
distinct from the rest of the face, admits of several variations: thus
in the _Staphylinidæ_ and _Cleridæ_ it is transverse and linear; in
_Copris_ it is triangular, with the vertex of the triangle truncated;
in _Vespa Crabro_ it is subquadrate and sinuated. In many Heteromerous
beetles[1411] it is rounded posteriorly: in _Pelecotoma_, a new genus
in this tribe, related to _Asida_, there is a deep anterior sinus; in
_Blaps_ the anterior margin is concave; in _Cetonia_[1412] _Brownii_,
and _atropunctata_ (forming a distinct subgenus), it is bifid: it
varies in the _Scarabæidæ_, in some being bidentate, in others
quadridentate, and in others again sexdentate, including the cheeks:
in _Mylabris_, a kind of blister-beetle, it is transverse and nearly
oval; in _Lamia_, a capricorn-beetle, it represents a parallelogram;
and in most _Orthoptera_ it is subtriangular: in _Tettigonia_ F. it
is prominent, transversely furrowed, and divided by a longitudinal
channel: in _Otiocerus_ K. it presents the longitudinal section of
a cone[1413]: in the _Diptera_ Order, with the exception of the
_Tipulidæ_ and some others, in which it unites with the cheeks, &c. to
form a rostrum, the nose in general, as to _form_, answers to its name,
resembling that of many of the _Mammalia_: in some of the _Asilidæ_
it is very tumid at the end, and terminates in a sinus, to permit
the passage of the proboscis to and fro: in many of the _Syrphidæ_,
&c. it is first flat and depressed, and then is suddenly elevated,
so as to give the animal's head the air of that of a monkey: in some
tribes, as _Rhingia_, _Nemotelus_, _Eristalis_, &c., in conjunction
with the cheeks it forms a conical rostrum: in _Tabanus bovinus_, and
other horse-flies, it terminates in three angles or teeth. Many more
forms might be mentioned, but these will suffice to give you a general
idea of them. In _size_ and _proportions_ the nose also varies. It
is frequently, as in _Tettigonia_, the most conspicuous part of the
face, both for size and characters; but in the _Staphylinidæ_ it is
very small, and often scarcely discernible, being overshadowed by its
ample front: and it may be observed in general, that when the antennæ
approximate the mouth, as in this genus and many others, the _front_
becomes _ample_, and the _nose_ is reduced to its _minimum_: but when
they are distant from the mouth, the reverse takes place; and the
nose is at its _maximum_ and the front at its _minimum_. _Mutilla_,
_Myrmecodes_, _Scolia_, &c. in the _Hymenoptera_, are an example of
the former; and the _Pompilidæ_, _Sphecidæ_, _Vespidæ_, &c. of the
latter. In _Myopa buccata_, &c. its length exceeds its width; but more
commonly the reverse takes place. The _circumscription_ of the _nose_
also deserves attention. It is usually terminated behind by the front
(_frons_), or, where it exists, by the _postnasus_, in the sides by the
cheeks, and anteriorly by the _labrum_. But this is not invariably the
case; for in the _Cimicidæ_, in which the cheeks form the bed of the
_Promuscis_, the front embraces it on each side by means of two lateral
processes, that sometimes meet or lap over each other anteriorly, which
gives the nose the appearance of being insulated; but it really dips
below these lobes to join the _labrum_. This structure you may see in
_Edessa_ F., and many other bugs. This part sometimes has its _arms_.
Thus in _Copris_, and many _Dynastidæ_, the horns of the head seem, in
part at least, to belong to this portion of it; in _Tipula oleracea_
(the crane-fly), &c. it terminates before in a horizontal mucro. In
_Osmia cornuta_, a kind of wild-bee, each side of the nose is armed
with a vertical horn. The _margin_ of the nose in most Lamellicorn
insects, though mostly level, curves upwards.

I am next to mention a part of the nose which merits a distinct
name and notice, which I conceive in some sort to be analogous to
the _nostrils_ of quadrupeds, and which I have therefore named the
_Rhinarium_ or nostril-piece. I had originally distinguished it by
the plural term _nares_, nostrils; but as it is usually a single
piece, I thought it best to denote it by one in the singular. When
I treat of the senses of insects, I shall give you my reasons, as I
have before said, for considering this part as the organ of scent,
or connected with it, which you will then be able to appreciate.
I shall only here observe, that the piece in question is in the
usual situation of the nostrils--between the nose and the lip.
In a large number of insects this part may be regarded as nearly
obsolete; or at least it is merely represented by the very narrow
membranous line that intervenes between the nose and the lip and
connects them; which, as in the case of the head of _Harpali_
before noticed, may be capable of tension and relaxation, and so
present a greater surface to the action of the atmosphere. But I
offer this as mere conjecture. In the lady-bird (_Coccinella_) this
line is a little wider, and becomes a distinct _Rhinarium_; as it
does also in _Geotrupes_. With respect to its _insertion_, the
_rhinarium_ is a piece that either entirely separates the nose from
the lip, or only partially: the former is the most common structure.
It is particularly remarkable in a New Holland genus of chafers
(_Anoplognathus_ Leach). In _A. viridiæncus_ it is very ample, and
forms the under side of the recurved nose, so that a large space
intervenes between the margin of the latter and the base of the
_labrum_. In _Macropus_ Thunb., of the Capricorn tribe (_Cerambyx_
L.), the nostril-piece, which forms a distinct segment, is narrower
than the nose, and the upper-lip than the nostril-piece, forming as
it were a triple gradation from the front to the mouth. Again, in
others the part in question is received into a sinus of the nose.
This is the case with the dragon-flies (_Libellulina_), in which this
sinus is very wide; in the burying-beetle (_Necrophorus_)[1414], in
some species of which it is deep but narrow; and in a species of
_Tenebrio_ from New Holland, which perhaps would make a subgenus.
If you examine with a common glass any of the larger rove-beetles
(_Staphylinidæ_), you will find that the nose itself seems lost in
the nostril-piece, both together forming a very narrow line across
the head above the _labrum_, without any apparent distinction between
them; but if you have recourse to a higher magnifier, you will find
this divided into an upper and lower part, the former of the hard
substance of the rest of the head, and the latter membranous. I once
was of opinion that the prominent transversely furrowed part, so
conspicuous in the face of _Tettigonia_ F.[1415], was the _front_:
but upon considering the situation of this, chiefly below the eyes
and antennæ, and comparing it with the analogous piece in _Fulgora
laternaria_ and other insects of the Homopterous section of the
_Hemiptera_, I incline to think that it represents the _nose_, and
that the longitudinal ridge below it is the nostril-piece[1416].
In the Heteropterous section it is merely the vertical termination
of their narrow nose. In other insects again, this part approaches
in some measure to the common idea of nostrils; there being _two_,
either one on each side the nose, or two approximated ones. If you
catch the first humble-bee that you see busy upon a flower, you will
discover a minute membranous protuberance under each angle of the
nose. Something similar may be observed in some species of _Asilus_
L. In the _Orthoptera_, especially in _Blatta_, _Phasma_, and some
_Locustæ_, two roundish or square pieces, close to each other on the
lower part of the nose, represent the nostrils[1417].--With regard to
_substance_, in the chafer-tribes, at least those that feed on leaves
or living vegetable matter, as the _Melolonthidæ_, _Anoplognathidæ_,
and in many other insects, the _rhinarium_ is of the same substance
with the rest of the head; but in _Macropus_ Thunb., _Staphylinus_,
_Necrophorus_, &c., it consists of membrane.

ii. _Postnasus_[1418].--This is a part that appears to have been
confounded by Entomologists with the front of insects; in general,
indeed, it may be regarded as included in the nose, and does not
require separate notice: but there are many cases in which it is
distinctly marked out and set by itself, and in which it forms a
useful diagnostic of genera or subgenera. There is a very splendid and
beautiful Chinese beetle, to be seen in most collections of foreign
insects (_Sagra purpurea_), in which this part forms a striking
feature, and helps to distinguish the genus from its near neighbour
_Donacia_. If you examine its face, you will discover a triangular
piece, below the antennæ and above the _nasus_, separated from the
latter and from the front by a deeply-impressed line: this is the
_postnasus_ or _after-nose_. Again: if you examine any specimens of a
Hymenopterous genus called by Fabricius _Prosopis_ (_Hylæus_ Latr.),
remarkable for its scent of baum, you will find a similar triangle
marked out in a similar situation[1419]. In many Coleopterous
insects, besides _Sagra_, you will discover traces of the part we are
considering: as in _Anthia_, _Dytiscus_, and several others of the
Predaceous beetles. In _Cistela_ it is larger than the nose itself;
but it is more conspicuous in the _Orthoptera_, particularly in
_Locusta_ (_Gryllus_ F.), in which it is the space below the antennæ,
distinguished by two or four rather diverging ridges[1420]. In the
_Libellulina_, _Myrmeleonina_, &c. it is a distinct transverse piece.
In _Dasyga_ Latr., a kind of bee, it is armed with a transverse ridge
or horn--But enough has been said to render you acquainted with it; I
shall therefore proceed to the next piece.

iii. _Frons_[1421].--The _Front_ of insects may be denominated the
_middle_ part of the face between the eyes, bounded anteriorly by the
nose, or after-nose, where it exists, and the cheeks; laterally by
the eyes; and posteriorly by the vertex. Speaking properly, it is the
region of the _antennæ_; though when these organs are placed before
the eyes, under the margin of the nose, as in many Lamellicorn and
Heteromerous beetles, they seem to be rather _nasal_ than _frontal_.
This part is often elevated, as in the elastic beetles (_Elater_),
whose faculty of jumping, by means of a pectoral spring, has been
related to you[1422]. In _Anthia_, a Predaceous beetle, it has
often three longitudinal ridges. In many of the Capricorn beetles
(_Cerambyx_ L.), it is nearly in the shape of a Calvary cross, with
the arms forming an obtuse angle, and then terminating at the sinus
of the eyes in an elevation for the site of the antennæ. In the
ants also (_Formicidæ_), the front is often elevated between those
organs. In _Ponera_, one tribe of them, this elevation is bilobed,
and receives between its lobes the vertex of the _postnasus_. In
the hornet (_Vespa Crabro_) the elevation is a triangle, with its
vertex towards the mouth. In _Sagra_ it is marked out into three
triangles, the _postnasus_ making a fourth, with the vertexes
meeting in the centre. In the _Dynastidæ_ and _Scarabæidæ_ the
horns are often _frontal_ appendages, as is that of _Empusa_ Latr.,
a leaf-insect, and probably those of _Sphinx Iatrophæ_ F., which
affords a singular instance of a horned Lepidopterous one. Sometimes
it is an ample space, reducing the nose to a very narrow line, as in
the _Staphylinidæ_, or sending forth a lobe on each side, as before
mentioned, which embraces the nose. In a species of bug from Brazil,
related to _Aradus_ F., these lobes are dilated, foliaceous, and
meet before the nose, so as to form a remarkable extended frontlet
to the head. In others this part is extremely minute: thus in many
_male_ flies and other insects, as the _Libellulina_, where the
eyes touch each other, the front is cut off from the vertex and
reduced to a small angle. In the female flies the communication
with the vertex is kept open, and the front consequently longer.
In the horse-flies (_Tabanidæ_), in _Hæmatopota_, and _Heptatoma_,
the frontal space is wider than in the rest of that tribe. Many
of these are distinguished by a levigated area behind the antennæ
in the part we are treating of. In the _Libellulina_, and in the
drone-bee, whose eyes are confluent, the stemmata are in the front.
In many _Orthoptera_ also, as _Locusta_ Leach, one of them is below
the antennæ; and in the lanthorn-fly tribe (_Fulgoridæ_), both these
organs, which are situate between them and the eyes, as they do also
in _Truxalis_, appear to be in it[1423]. In this tribe the rostrum is
an elongation of the part in question; and perhaps you would think
at first that what I have considered as the _nose_ in _Tettigonia_
F. was also a tendency to this kind of rostrum; but if you examine
the great lanthorn-fly (_Fulgora laternaria_), you will find besides,
at the lower base of the lanthorn, a triangular piece analogous to
the nose of _Tettigonia_, and below it another representing its
nostril-piece:--the horizontal part of the nose in that genus may
perhaps be regarded as part of the front. In _Truxalis_ F. the face
consists of a supine and prone surface, and the latter is composed
of the front, after-nose, nose, and organs of the mouth. I may
notice here a most remarkable and singular tribe of bugs, of which
two species have been figured by Stoll[1424]: in these the head,
or rather those parts of it that we have now been describing, the
nose, namely, the after-nose, and front, are absolutely divided
longitudinally in two, each half having an eye and antenna planted in
it; or perhaps, as it is stated to be divided in one instance to the
commencement of the _promuscis_, the nose is left intire, and dips
down, as in cases before alluded to: so that in this the nose appears
to leave the lobes of the front, which in others embrace its sides.

iv. _Vertex_[1425].--We now come to the _vertex_, or crown of the head;
which is situated behind the front, and, except where the communication
is intercepted by confluent eyes, adjoins it. It is laterally bounded
by the hind part of the eyes and the temples; and _posteriorly_, where
that part exists, by the _occiput_. The vertex may be denominated the
ordinary region of the _stemmata_: for though in several cases, as
we have just seen, one or more of them are planted in the front; yet
this in the great majority, especially in the _Hymenoptera_, is their
natural station. In _Blatta_ and some other _Orthoptera_ the posterior
angle of the head is the vertex. In many dung-chafers of Latreille's
genus _Onthophagus_, which are said to have _occipital_ horns, as _O.
nutans_, _nuchicornis_, _Xiphias_, &c., the horn really arms the part
I regard as the vertex. In _Locusta_ Leach, this part is very ample,
and in _Truxalis_ very long; but more generally it is small, and not
requiring particular notice.

v. _Occiput_[1426].--The _occiput_, or _hind-head_, is that part of
the face that either forms an angle with the vertex posteriorly,
or slopes downwards from it. It has for its lateral boundaries the
temples, and behind it is either terminated by the orifice of the
head, or in many cases by the neck. In those beetles that have no
neck, as the Lamellicorn and Capricorn, the hind-head is merely a
declivity from the vertex, usually concealed by the shield of the
thorax, very lubricous, to facilitate its motion in the cavity of
that part, and at its posterior margin distinguished by one or two
notches, which I shall notice hereafter, for the attachment of the
levator muscles: but in those beetles or other insects that have
a neck, or a versatile head, the occiput forms an angle with the
vertex, often rounded, and sometimes acute. This structure may be
seen in Latreille's _Trachelides_, and several other beetles. In the
_Hymenoptera_, _Diptera_, and others with a versatile head, the part
now under consideration curves inwards from the vertical line, so
as with the temples and under parts of the head to form a concavity
adapted to its movement upon the trunk.

vi. _Genæ_[1427].--The _cheeks_ of insects (_Genæ_) usually surround
the anterior part of the eyes, and lie between them and the mandibles
or their representatives. Where they approach the latter, as in the
Predaceous beetles (_Cicindela_, _Carabus_ L. &c.), they are very
short, and of course longer where the eyes are further removed from
the mouth; as in the Rhyncophorous beetles (_Curculio_ L.), where
they form the sides of the rostrum, and often contain a channel which
receives the first joint of the antennæ, when they are unemployed.
In the _Scarabæidæ_ and many other Lamellicorn beetles, their
separation on each side from the nose is marked by a ridge[1428];
and in the wasps (_Vespa_) by an impressed line or channel. In an
African tribe at present arranged with _Cetonia_ F., to which _C.
bicornis_ Latr.[1429] and another, which he has named, I believe, _C.
vitticollis_, belong, the cheeks are porrected on each side of the
mouth into a horizontal horn. These horns have at first the aspect
of a pair of open mandibles. In the magnificent _Goliathi_ Lam.,
the horns of the male are rather a process of the _cheek_ than of
the _nose_. In _Alurnus_, _Hispa_, and other beetles, these parts,
by their elevation and conjunction with the lower side of the head,
form a kind of fence which surrounds and protects the oral organs;
in many _Cimicidæ_, by a similar elevation of the cheeks, the bed
of the _promuscis_ is formed. In the Homopterous _Hemiptera_ they
run parallel nearly with the _rhinarium_ or nostril-piece. In the
_Hymenoptera_ they are almost always ample, but they are confined
to the lower side of the eye. In _Sirex grandis_, and others of
that genus, the cheek at the base of the mandible is dilated so
as to form a rounded tooth below it. In the Capricorn-beetles it
is considerable, and sometimes terminates, at the base of the
mandible, in two or three notches. In _Scaurus_ and _Eurychora_,
darkling-beetles, the cheek below projects into a lobe that covers
the base of the _maxilla_. But the animal distinguished by the
most remarkable cheeks is a species of _Phryganea_ L. (_Phryganea
personata_ Spence); for from this part projects a spoon-shaped
process, which curves upwards, and uniting with that of the other
cheek, forms an ample mask before the face, the anterior and upper
margin of which, in the insect's natural state, are closely united;
and the posterior part being applied to the anterior part of the
eye, causes the face to appear much swoln. It looks as if it was a
single piece; but upon pressing the thorax it opens, both above and
in front, into two parts, each convex without and hollow within, and
each having attached to its inside a yellow tuft of hair resembling a
feather. The use of this machinery at present remains a mystery[1430].

vii. _Tempora_[1431].--The temples (_Tempora_) are merely a
continuation of the cheeks to the posterior limit of the head,
forming its sides and posterior angles, and including the hinder part
of the eyes, the vertex, and the occiput. They seldom exhibit any
tangible character, except in certain ants (_Atta_ Latr.), in which
their angle terminates in one or two strong spines, giving the animal
a most ferocious aspect; and in that remarkable genus _Corydalis_
they are armed below with a tooth or point, which was not overlooked
by De Geer[1432].

viii. _Oculi_[1433].--I must now call your attention to organs of more
importance and interest, and which indeed include a world of wonders: I
mean the eyes (_Oculi_) of insects. These differ widely from those of
vertebrate animals, being incapable of motion. They may be regarded as
of _three_ descriptions--_simple_, _conglomerate_, and _compound_.

1. _Simple Eyes_[1434]. We will consider them as to their _number_,
_structure_, _shape_, _colour_, _magnitude_, _situation_, and
_arrangement_.

As to their _number_, they vary from two to sixteen. In the flea,
the louse, the harvest-man (_Phalangium_), there are only _a pair_;
in the bird-louse of the goose (_Nirmus Anseris_), and probably in
others of the same genus, there are _four_[1435]; in some spiders
(_Scytodes_, _Dysdera_, and _Segestria_ Latr.[1436]), and some
scorpions[1437], there are _six_. In the majority of spiders and
_Scolopendra morsitans_, _Scorpio maurus_, &c. there are _eight_;
and in _Podura_ and _Sminthurus_ Latr. there are sixteen[1438].

As to their _structure_, nothing seems to have been ascertained;
probably their organization does not materially differ from that of one
of the lenses of a compound eye; which I shall soon explain to you.

Their _colour_ in the many is black and shining, but in the
bird-louse of the goose they are quite white and transparent.
In spiders they are often of a sapphirine colour, and clear as
crystal. In _Scolopendra morsitans_ and many spiders, scorpions,
and _phalangia_[1439], they appear to consist of iris and pupil,
which gives them a fierce glare, the centre of the eye being dark
and the circumference paler. In the celebrated _Tarantula_ (_Lycosa
Tarantula_), the pupil is transparent, and red as a ruby; and the
iris more opaque, paler, and nearly the colour of amber.

Where there are more than two, they vary in _magnitude_. In the
enormous bird-spider (_Mygale avicularia_) the four external eyes
are larger than the four internal[1440]; but in the Tarantula
and _Sphasus_, the _two_ or _four_ internal are the largest. In
_Clubiona_ and _Drassus_ they are all nearly of the same size[1441];
and in the _Micrommata_ family they are very small[1442].

They vary also in _shape_. In _Scolopendra morsitans_ the three
anterior ones are round, and the posterior one transverse, and
somewhat triangular. In _Mygale calpeiana_, a spider, the two
smallest are round and the rest oval[1443]. In the trapdoor or
mason spider (_Mygale cæmentaria_), the four small internal ones are
round, and the large external ones oval[1444]; and those that are
circumscribed posteriorly with an impressed semicircle, are shaped
like the moon when gibbous[1445].

The _situation_ and _arrangement_ of simple eyes are also various.
In many they are imbedded, as usual, in the head; but in the little
scarlet mite, formerly noticed[1446], (_Trombidium holosericeum_),
they stand upon a small foot-stalk[1447]: the hairiness of this
animal might otherwise have impeded its sight. In spiders they
are planted on the back of the part that represents the head,
sometimes four on a central elevation or tubercle, and the remaining
four below it--as in _Lycosa_; sometimes the whole eight are
on a tubercle, as in _Mygale_; and sometimes, as in the common
garden-spider (_Epeira Diadema_), upon three tubercles, four on the
central one and two on each of the lateral ones. Other variations
in this respect might be named in this tribe. In the scorpions a
pair are placed one on each side, on a dorsal tubercle, and the
other four or six on two lateral ones of the anterior part of the
head[1448]. In the _Phalangidæ_ the _frontal_ eyes of the scorpion
cease, and only a pair of _dorsal_ ones are inserted vertically
in the sides of a horn or tubercle, either bifid or simple, often
itself standing upon an elevation which emerges from the back of
the animal[1449]. If their eyes were not in a vertical and elevated
position, the sight of these insects would be very limited; but by
means of the structure just stated, they get a considerable range of
surrounding objects, as well as of those above them. With regard to
the _arrangement_ of the eyes we are considering, it varies much.
Sometimes they are placed nearly in the segment of a circle, as
in those spiders that have _six_ eyes only, before noticed[1450];
sometimes in two straight lines[1451]; at others in two segments of
a circle[1452]; at others, in _three_ lines[1453], and at others
in _four_[1454]. Again, in some instances they form a cross, or
two triangles[1455]; in others, two squares[1456]; in others, a
smaller square included in a large one[1457]; in others, a posterior
square and two anterior triangles[1458]; sometimes a square and two
lines. Though generally separate from each other, in several cases
two of the eyes touch[1459]; and in one instance three coalesce
into a triangle[1460]. But it would be endless to mention all the
variations, as to arrangement, in the eyes of spiders.

2. _Conglomerate Eyes_[1461] differ in nothing from simple eyes, except
that instead of being dispersed they are collected into a body, so
as at first sight to exhibit the appearance of a compound eye:--they
are, however, not hexagonal, and are generally convex. They occur
in _Lepisma_, the _Iulidæ_, and several of the _Scolopendridæ_. In
_Scolopendra forficata_ the eye consists of about twenty contiguous,
circular, pellucid lenses, arranged in five lines, with another larger
behind them, as a sentinel or scout, placed at some little distance
from the main body. In the common millepede (_Iulus terrestris_) there
are twenty-eight of these eyes, placed in seven rows, and forming a
triangle, thus [Illustration: triangular eye shape]--the posterior row
containing seven lenses, the next six, and so on, gradually losing one,
till the last terminates in unity. Each of these lenses is umbilicated,
or marked with a central depression. In _Craspedosoma_ Leach, you will
find a similar formation. In _Glomeris zonata_, a kind of wood-louse
that rolls itself into a ball, the lenses are arranged in a line curved
at the lower end, with a single one by itself at the posterior end on
the outside; they are oblong and set transversely, and their white
hue and transparency give them the appearance of so many minute gems,
especially as contrasted with the black colour of the animal[1462].
Between these eyes and the antennæ is another transverse linear white
body, but opaque, seemingly set in a socket, and surrounded by a white
elevated line, like the bezel of a ring. Whether it is an eye, or what
organ, I cannot conjecture[1463]. Its aspect is that of a spiracle.

3. _Compound Eyes_[1464].--These are the most common kind of eye
in hexapod insects, when arrived at their perfect state; in their
larva state, as we have seen, their eyes being usually simple[1465];
except, indeed, those whose metamorphosis is _semicomplete_, which
have compound eyes in every state.--In considering compound eyes, I
shall advert to their _structure_, _number_, _situation_, _figure_,
_clothing_, _colour_, and _size_.

As to their _structure_,--when seen under the microscope they appear
to consist usually of an infinite number of convex _hexagonal_
pieces. If you examine with a good glass the eye of any fly, you
will find it traversed by numberless parallel lines, with others
equally numerous cutting them at right angles, so as apparently to
form myriads of little squares, with each a lens of the above figure
set in it. The same structure, though often not so easily seen,
obtains in the eyes of _Coleoptera_ and other insects. When the eye
is separated and made clean, these hexagons are as clear as crystal.
Reaumur fitted one eye to a lens, and could see through it well, but
objects were greatly multiplied[1466]. In Coleopterous insects they
are of a hard and horny substance; but in _Diptera_, &c. more soft
and membranous. The number of lenses in an eye varies in different
insects. Hooke computed those in the eye of a horse-fly to amount
to nearly 7,000[1467]; Leeuwenhoeck found more than 12,000 in that
of a dragon-fly[1468]; and 17,325 have been counted in that of a
butterfly[1469]. But of all insects they seem to be most numerous in
the beetles of Mr. W. S. MacLeay's genus _Dynastes_. In the eyes of
these the lenses are so small as not to be easily discoverable even
under a pocket microscope, except the eye has turned white[1470]: it
is not, therefore, wonderful, that Fabricius should call these eyes
_simple_[1471]. In some insects, however, as in the _Strepsiptera_
Kirby, the lenses are not numerous: in _Xenos_ they do not exceed
fifty, and are distinctly visible to the naked eye[1472]. These
lenses vary in magnitude, not only in different, but sometimes in
the same eyes. This is the case in those of male horse-flies and
flies, those of the upper part of the eye being much larger than
those of the lower[1473]. The partitions that separate the lenses,
or rather bezels, in which they are set, are very visible in the
eyes just mentioned, and those of _Xenos_; but in many insects they
are only discernible at the intersecting lines of separation between
the lenses. In hairy eyes, such as those of the hive-bee, the hairs
emerge from these _septa_. Every single lens of a compound eye may be
considered as a _cornea_, or a _crystalline humour_, it being convex
without and concave within, but thicker in the middle than at the
margin: it is the only transparent part to be found in these most
remarkable eyes. Immediately under the _cornea_ is an opaque varnish,
varying according to the species, which produces sometimes in one
and the same eye spots or bands of different colours. These spots
and bands form a distinguishing ornament of many of the _Tabani_ and
other flies. And to this varnish the lace-winged flies (_Hemerobius_,
&c.) are indebted for the beautiful metallic hues that often adorn
them. When insects are dead, this varnish frequently loses its
colour, and the eye turns white: hence many species are described
as having _white_ eyes which when alive had _black_ ones. The
consistence of this covering is the same with that of the varnish
of the _choroid_ in the eyes of vertebrate animals; but it entirely
covers the underside of the lens, without leaving any passage for the
light. Below this varnish there are numbers of short white hexagonal
prisms[1474], every one of which enters the concavity of one of the
lenses of the cornea, and is only separated from it by the varnish
just described: this may be considered as the _retina_ of the lens
to which it is attached; but at present it has not been clearly
explained how the light can act upon a _retina_ of this description
through an opaque varnish. Below this multitude of threads (for such
the bodies appear), perpendicular to the _cornea_, is a _membrane_
which serves them all for a base, and which consequently is nearly
parallel with that part. It is very thin, of a black colour, not
produced by a varnish; and in it may be seen very fine white
_tracheæ_, which send forth branches still finer, that penetrate
between the prisms of the _cornea_: this membrane may be called
the _choroid_. Behind this is a thin expansion of the optic nerve,
which is a true nervous membrane, precisely similar to the _retina_
of red-blooded animals. It appears that the white pyramidal threads
which form the _retina_ of each lens are sent forth by this general
_retina_, and pierce the choroid by a number of almost imperceptible
holes[1475]. From this description it appears that the eyes of
insects have nothing corresponding with the _uvea_ or _humours_ of
those of vertebrate animals, but are of a type peculiar to themselves.

Having explained to you the wonderful and complex structure with
which it has pleased the CREATOR to distinguish the organs of vision
of these minute beings, proving, what I have so often asserted,
that when animals seem approaching to nonentity, where one would
expect them to be most _simple_, we find them in many cases most
_complex_, I shall now call your attention to the next thing I am
to consider--the _number_ of the eyes in question. Most insects
have only _two_; but there are several exceptions to this rule.
Those that have occasion to see both above and below the head,
the eyes of all being immovable, must have them so placed as to
enable them to do this. This end is accomplished in many beetles,
for instance _Scarabæus_ L., _Helæus_ Latr., &c., by having these
organs fixed in the _side_ of the head, so that part looks upward
and part downward; but in others _four_ are given for this purpose.
If you examine the common whirlwig (_Gyrinus Natator_) that I have
so often mentioned[1476], which has occasion, at the same time,
to observe objects in the air and in the water, you will find it
is gifted with this number of eyes. _Lamia Tornator_ (_Cerambyx
tetrophthalmus_ Forst.) and some others, of which I make a genus,
under the appellation of _Tetrops_, are also so distinguished. In
these insects, one eye is above and the other below the base of
the antennæ; in fact, in these the _canthus_, instead of dividing
the eye partially, as in the other Capricorn-beetles, runs quite
through it at considerable width[1477]. In _Ryssonotus_ MacLeay
(_Lucanus nebulosus_ K.) the eye appears also to be divided in two
by the _canthus_. In the _Neuroptera_ Order there is more than one
instance of the same kind. In _Ascalaphus_ there are two considerable
eyes on each side of the head, which, though clearly distinct, meet
like those of many male flies and the drone. The male, likewise,
of more than one species of _Ephemera_, besides the common lateral
eyes and the _stemmata_ on the back of the head, have a pair of
compound eyes on the top of a short columnar process[1478]. In the
_Hemiptera_ Order, also, an instance occurs of four eyes in the
genus _Aleyrodes_[1479]. Amongst the vertebrate animals, there
is an example of eyes with two pupils in _Anableps_, a genus of
fishes[1480], but no vertebrate animal has _four_ of these organs.
That many insects should have more than _two_ eyes, will not seem
to you so extraordinary as that any should be found that, like the
Cyclops of old, have only _one_. There is, however, an insect,
before celebrated for its agility[1481] (_Machilis polypoda_ Latr.),
which has a single eye in its forehead; or we may say, its eyes
are confluent, without any line of distinction between them except
a small notch behind. Now that I am treating of the _number_ of
eyes, I must not forget to observe to you, that in some insects no
eyes at all have been discovered. In _Polydesmus complanatus_, on
each side of the head there is an eye-shaped portion separated by a
suture, in which under a powerful lens I cannot satisfy myself that
I can discern any thing like the facets that usually distinguish
compound eyes. In _Geophilus electricus_, another myriapod, they
certainly do not exist[1482]. Whence we may conclude, as was before
observed[1483], that the faculty of emitting light is rather given it
as a means of defence than to guide it in its path.

The _situation_ of compound eyes differs in different tribes. In
some, as in the _Staphylinidæ_, they are planted laterally in the
_anterior_ part of the head; in others, the _Carabi_ &c., in the
_middle_; in others again, _Locusta_ Leach &c., in the _posterior_
part. In some, their station is more in the upper surface, either
before or behind; so that a very narrow space separates them, or
perhaps none at all. Instances of this position of the eyes occur
in a minute weevil (_Ramphus_ Clairv.[1484]), and many _Diptera_,
&c. Of those that form an union on the top of the head, some are
placed obliquely, so as to leave a diverging space below them,
as in many _Libellulina_[1485], the drone[1486], &c. Others, as
_Atractocerus_, in which the eyes occupy nearly the whole head,
and unite anteriorly, have this diverging space _above_ their
conflux. In _Rhina barbirostris_ Latr., another kind of weevil,
they are confluent _below_ the head, at the base of the rostrum,
and a very narrow interval separates them above. In a large number
of the _Heteromerous_ beetles, they are set _transversely_, in the
_Capricorn_ ones _longitudinally_. Their surface, when they are
lateral, has usually two aspects, one _prone_ to see below, the other
_supine_ to see above. In general the eyes are situated behind the
antennæ, so that their position, whether it shall be anterior or
posterior, depends upon that of those organs. Often, indeed, as in
the last-named beetles, part of the eye is behind and part before the
antennæ; but except where there are _four_ eyes, as in _Tetrops_,
they are never placed before or below them.

Though the eyes of insects are generally _sessile_, yet to give them
a wider range they are sometimes, but it rarely occurs, placed, like
those of many _Crustacea_, on a _footstalk_, but not a _moveable_
one. An instance of this in certain male _Ephemeræ_ has already been
mentioned. In the _Hemiptera_ De Geer has figured two species of bugs
(_Cimicidæ_) that are so circumstanced[1487]; as are also all the known
_Strepsiptera_ K., though in these the footstalk is very short[1488]:
but the most remarkable example of columnar eyes is afforded by that
curious _Dipterous_ genus _Diopsis_, in which both eyes and antennæ
stand upon a pair of branches, vastly longer than the head, which
diverge at a very obtuse angle from its posterior part[1489].

In their _figure_ eyes vary much. Sometimes they are so prominent as
to be nearly _spherical_: this is the case with some aquatic bugs,
as _Ranatra_, _Hydrometra_, and several male _Ephemeræ_[1490]. Very
often they are _hemispherical_, as in the tiger-beetles (_Cicindela_
L.), and the clocks or dors (_Carabus_ L.); but in a large number
of insects they are flat, and do not rise above the surface of the
head.--With regard to their _outline_, they are often perfectly
_round_, as in many weevils; _oval_, as in various bees; _ovate_, as
in other bees (_Andrena_ F.); _triangular_, as in the water-boatman
(_Notonecta_). They are also often _oblong_, and occasionally narrow
and _linear_; as in that singular beetle _Helæus_. In many of the
_Muscidæ_ they form nearly a _semicircle_, or rather, perhaps, the
quadrant of a sphere. The eyes of the Capricorn-beetles (_Cerambyx_
L.) have a sinus on their inner side, as it were, taken out of them;
so that they more than half surround the antennæ, before which is the
longest portion of them. An approach to this shape is more or less
observed in the darkling-beetles (_Tenebrio_ L.); but in these the
sinus is not so deep. I may under this head observe, that in those
_Mantidæ_ that represent dry leaves, and some others, these organs
usually terminate in a spine[1491].

Though not distinguished by the beauty and animation that give such
interest to the eye of vertebrate animals, and exhibiting no trace of
iris or pupil, yet from the variety of their _colours_ the compound
eyes of insects, though most commonly black or brown, are often very
striking. Look at those of one of the lace-winged flies that commit
such havoc amongst the _Aphides_[1492], and it will dazzle you with
the splendour of the purest gold, sometimes softened with a lovely
green. The lenses of those of _Xenos_ blaze like diamonds set in
jet[1493]. You have often noticed the fiery eyes of many horse-flies
(_Tabanus_ L.) with vivid bands of purple and green[1494]. Others
are spotted[1495]; and Schellenberg has figured one (_Thereva
hemiptera_)[1496], that exhibits the figure of a flower painted in
red on a black ground. These colours and markings are all most vivid
and brilliant in the _living_ insect, and often impart that fire
and animation to the eyes for which those of the higher animals are
remarkable. Take one of the large dragon-flies that you see hawking
about the hedges in search of prey, examine its eyes under a lens, and
you will be astonished at the brilliance and crystalline transparency
which its large eyes exhibit, and by the remarkable vision of larger
hexagons which appear in motion under the _cornea_, being reflected by
the _retina_--all which give it the appearance of a living eye. This
moving reflexion of the hexagonal lenses in living insects was noticed
long since in some bees (_Nomada_ F., _Cœlioxys_ Latr.)[1497]

Compound eyes differ greatly in their _size_. In some insects,
as _Atractocerus_, the drone-bee, many male _Muscidæ_, &c., they
occupy nearly the whole of the head; while in others, as numerous
_Staphylinidæ_, _Locusta_ Leach, &c., they are so small as to be
scarcely larger than some simple eyes of spiders: and they exhibit
every intermediate difference of magnitude in different tribes,
genera, and species.

Under this head I must say something of the _Canthus_ of the eye;
by which I mean an elevated process of the cheek, which in almost
all the genera of the Lamellicorn beetles enters the eye more or
less, dividing the upper portion from the lower. Though usually
only a _process_ of the cheek, yet in the _Scarabæidæ_ the whole
of that part forms the _canthus_[1498]. It only _enters_ the eye
in the _Rutelidæ_, _Cetonidæ_, &c.; it extends through _half_ of
it in _Copris_; it goes _beyond_ the half in _Ateuchus_; and in
_Ryssonotus_ MacLeay (_Lucanus nebulosus_ K.) it quite divides the
eye into two[1499], as I before observed. In _Lucanus_, _Passalus_
&c. it projects before the eye into an angle; in _Lucanus femoralis_
nearly into a spine; but in _Lamprima_ and _Œsalus_ it does not
exist. The part, also, that enters the eye in the Capricorn-beetles
may be regarded as a kind of _canthus_, though it is merely a
dilatation of the _front_.

4. _Stemmata_[1500].--Having given so full an account of the kinds
and structure of the ordinary eyes of insects, you may perhaps expect
that I should now dismiss the subject: you would, however, have great
cause to blame me, did I not make you acquainted with a kind of
auxiliary eyes with which a large portion of them are gifted; I mean
those pellucid spots often to be found on the posterior part of the
front of these animals, or upon the vertex, frequently arranged in a
triangle. These, Linné, from his regarding them as a kind of coronet,
called _Stemmata_. They have been of late denominated _Ocelli_; but as
this latter term is also in general use for the eyelets on the wings
of _Lepidoptera_, I have adhered to that of the illustrious Swede.
Neither he nor Fabricius has expressed any opinion as to the _use_ of
these organs; but Swammerdam and Reaumur were aware that they were
real _eyes_. The former found that there are nerves that diverge to
them though not easily traced, and that they have a _cornea_, and
what he takes for the _uvea_[1501]; and the latter has supposed that
the compound eyes and these simple ones have, the one the power of
magnifying objects much, and the other but little, so that the former
are for surveying those that are distant, and the latter those that
are near[1502]. The same author relates some experiments that he tried
with the common hive bee, by which he ascertained that the _stemmata_,
as well as the compound eyes, were organs of vision. He first smeared
the _latter_ over with paint, and the animals, instead of making for
their hive, rose in the air till he lost sight of them. He next did the
same with the _former_, and placing the bees whose _stemmata_ he had
painted within a few paces of their hive, they flew about on all sides
among the neighbouring plants, but never far: he did not observe that
these ever rose in the air like the others[1503]. From this experiment
it seems as if the compound eyes were for _horizontal_ sight, and the
_stemmata_ for _vertical_.

The definition of them by Linné and Fabricius as smooth, shining,
elevated or hemispheric puncta, conveys a very inadequate idea of
them; for, except in a very few instances, they are perfectly clear
and transparent, and their appearance is precisely the same as that
of the simple eyes of _Arachnida_ &c., under which head they might
very well have been arranged; but as the last are _primary_ eyes, and
the stemmata _secondary_, it seemed to me best that they should stand
by themselves. The structure of both is probably the same, and their
internal organization that of one of the lenses of a compound eye,
and both are set in a socket of the head.

Though a large number of insects have them, they are by no means
universal, since some Orders, as the _Strepsiptera_, _Dermaptera_, and
_Aptera_, are altogether without them. The _Coleoptera_, also, have
been supposed to afford no instance of species furnished with them;
but in the last number of Germar and Zincken Sommer's _Magasin_, it is
affirmed that they are discoverable in Gravenhorst's genus _Omalium_,
but not in the kindred genera _Micropeplus_ and _Anthophagus_[1504].
Upon examining the former genus, I find, that although _Omalium
planum_ and affinities, _O. striatulum_, and some others, appear
not to have them, yet with the aid of a good magnifier they may be
discovered in most species of that genus; as likewise in _Evœsthetus_
Grav. I find them also very conspicuous in _A. Caraboides_ and other
_Anthophagi_, but some species appear to want them. In these insects
they are two in number, situated in the vertex a little behind the
eyes but within them, and either at each end of a transverse furrow,
or at the posterior termination of two longitudinal ones. Nor are they
found in all the genera of the other Orders. In the _Orthoptera_, the
_Blattidæ_, unless a white smooth spot on the inner and upper side of
the eyes may be regarded as representing them, have them not; but in
all the other genera of that Order they are to be found[1505]. In the
_Hemiptera_ all the _Cicadiadæ_ are gifted with them; as are likewise
_Tetyra_, _Pentatoma_, with many other _Cimicidæ_, and the _Reduviadæ_
very remarkably; but many others in both sections of this order, as
_Thrips_, _Coccus_, _Aphis_, _Capsus_, _Miris_, _Naucoris_, _Nepa_, and
_Notonecta_, &c. are deprived of them[1506]. Of the _Neuroptera_ the
_Libellulina_ add _stemmata_ to their large eyes, in the anterior angle
of which they are stationed[1507]; but many other genera of that Order
are without them; as _Myrmeleon_, _Ascalaphus_, _Hemerobius_, &c. The
_Trichoptera_ and _Lepidoptera_ universally have them; though in the
latter, except in _Castnia_ and the _Sphingidæ_, they are not easily
seen. In the _Hymenoptera_ they are usually very conspicuous, but in
_Larra_ and _Lyrops_, two genera of this order, the posterior pair are
scarcely discernible; and in the neuter ants they are quite obsolete.
In the _Diptera_, though many genera are furnished with them, yet many
also want them; amongst the rest Latreille's _Tipulariæ_, and all the
horse-flies (_Tabanus_ L.). The _Pupiparæ_ (_Hippobosca_ L.) usually
have none; but in _Ornithomyia avicularia_, one of that tribe, though
extremely minute they are visible, arranged in a triangle, in the
polished space of their vertex.

As to the _Number_ of the _stemmata_, _three_ appears to be most
universal. Reaumur mentions an instance in which he counted _four_ in
a fly with two threads at its tail; but great doubt rests upon this
statement[1508]. Some Orthopterous genera, as _Gryllotalpa_, and many
Hemipterous, as _Tetyra_, _Pentatoma_, _Reduvius_[1509], _Cercopis_,
_Fulgora_[1510], &c., have no more than _two_; and in _Larra_ and its
affinities, as just observed, the posterior ones are obsolete, so as
to leave only _one_ discernible.

Where there are _three_ of these organs, they are usually arranged in
an obverse _triangle_ in the space behind the antennæ, at a greater
or less distance from them. In those male flies (_Muscidæ_) whose
eyes are confluent, the _stemmata_ are in a little area _behind_
their conflux; but, as before observed, in the drone-bee and the
_Libellulina_ they are _before_ it. This triangle is in some cases
nearly _equilateral_, as in _Perla_ related to the may-flies, and
many _Hymenoptera_; in others it is _acutangular_, as in _Locusta_
&c., in which the _stemma_ forming the vertex of the triangle is
before the antenna[1511]: in others, again, it is _obtusangular_,
as you will see in _Pepsis_ and various _Hymenoptera_. In the
humble-bees (_Bombus_), a line drawn through them would form a slight
curve. Their _situation_ also varies. In insects that have only
_two_, they are sometimes placed a little _behind_ the eyes, or in
the back part of the space between them: this is the case with most
of the bugs (_Cimex_ L.) that have them.--They are often _distant_,
as in _Tetyra_ F., _Edessa_ F.; and sometimes _approximated_, as
in _Reduvius_ F.[1512] In many of the Homopterous _Hemiptera_, as
_Cercopis_, _Ledra_, &c. they are planted in the _upper_ part of
the head[1513], but in _Iassus_ their situation is on the _under_
part; and in a North American subgenus, as yet without a name, they
are exactly _between_ the two, being placed in the frontal angle.
In _Fulgora_ their station is between the eyes and antennæ[1514].
They are most commonly _sessile_, and as it were _set_ in the head;
but in some, as _Fulgora candelaria_, they stand on a _footstalk_.
The _stemmata_ are set in the side of a frontal tubercle in that
four-winged fly of threatening aspect, _Corydalis_, which in its
_perfect state_ has mandibles, but longer and more tremendous,
like those that distinguish the _larva_ only of the kindred genus
_Hemerobius_[1515]. These organs differ little in _shape_, being
usually perfectly _round_ and somewhat _convex_; but occasionally
they vary in this respect. In _Fulgora serrata_ they are _oblong_,
with a longitudinal depression; in _F. Diadema_ they are also
umbilicated, but the _umbilicus_ is circular; in _Corydalis_ they are
_oval_; in other insects they are _ovate_; in some _semicircular_,
and in a few _triangular_. They vary much in _size_: in some of
these animals being so minute as to be scarcely visible, while in
others, as _Corydalis_, _Dorylus_, _Vespa pallida_ F., _Reduvius_,
&c.[1515], they are as large as some compound eyes. They differ also
in _colour_, though often _black_: in _Fulgora laternaria_ they
are of a beautiful _yellow_; in F. _candelaria_ they are _white_;
in many _Hymenoptera_ they are _crystalline_, in others _red_: the
fierce look of _Reduvius personatus_ is rendered more hateful by its
_stemmata_ having a pale iris round a dark pupil[1516].

Let us here stop and adore the goodness of a beneficent CREATOR, who,
though he has deprived these little beings of the _moveable_ eyes
with which he has gifted the higher animals, has made it up to them
by the variety and complex structure of their organs of vision, where
_we_ have only _two_ points of sight, giving _them_ more than as many
_myriads_.

5. _Antennæ._--But of all the organs of insects, none appear to be
of more importance to them than their _Antennæ_, and none certainly
are more wonderful and more various in their structure, and probably
uses. Upon this last particular I shall enlarge hereafter. Their
structure, as far as it differs in the sexes, I fully discussed in
a former letter[1517]; and the most remarkable kinds of them will
be included in a set of definitions which I shall draw up for you
before our correspondence on this part of my subject closes: I shall
therefore now confine myself to the following particulars--namely,
their _number_, _insertion_, _substance_, _situation_, _proportion_,
_general form_ and _structure_, _clothing_, _expansion_, _motions_,
and _station of repose_.

As to their _Number_, in the majority of _crustaceous_ animals the
antennæ amount to _four_, but no _insect_ has more than _two_. A
genus recently established (_Otiocerus_ Kirby[1518]) seems to afford
an exception to this rule, since the species composing it at first
sight appear to have _four_, and in some instances even _six_ antennæ;
but as only _two_ of them terminate in a bristle, the other, though
proceeding from the same bed of membrane, may perhaps be regarded
as merely appendages. Germar, who has described a species of this
genus[1519] under the name of _Cobax Wintheri_, considers these
appendages as analogous to _palpi_: but as they do not proceed from
the _oral_ organs, but from the bed of the _antennæ_ at the base of the
nose[1520], they ought certainly to be regarded rather as accessories
to the latter, than as representing the former. In the _Aptera_ order
the mites (_Acacus_ L.) appear to be without these organs. In the
pupiparous tribe _Hippobosca_ they seem about to disappear; and in
the _Arachnida_ &c., as has been more than once observed[1521], the
_mandibulæ_ have been thought to represent, not indeed the antennæ of
_insects_, but the _inner_ pair of those of the _Crustacea_.

In considering the _insertion_ of antennæ, by which I mean their
articulation with the head, we must advert first to the orifice
(_Torulus_) that receives them[1522]. This is a perforation of the
crust of the head; commonly, though not invariably, circular: in
Coleopterous insects often with concave lubricous sides, forming
an acetabulum, with processes usual in ginglymous articulations,
larger than the bulb or root of the antennæ; and which is commonly
covered, except the central space occupied by the bulb, with a
tense membrane. Though not in general remarkable, in some cases
it merits attention. In the genus _Rhipicera_ Latr., the elegant
antennæ of whose males I have described in a former letter[1523],
particularly the Brazilian species, it is a long process on each side
of the nose, and might be mistaken for the first joint: in another
Coleopterous genus, _Priocera_ K.[1524], it has somewhat of the
shape of a trumpet: in _Cupes_ a tubercle rises just above the base
of the antenna: a circular process forms the torulus in _Fulgora_
and others. It is also often placed in a cavity of the front, as in
several wild-bees, _Melitta_ K., and in _Locusta_ Leach on the sides
of an elevation of that part[1525]. In a large majority of insects
the bulb (_Bulbus_) or ball which is received by the bed, wears the
appearance, especially in the _Hymenoptera_, of a distinct joint; but
if you carefully examine it, you will clearly see that it is merely
the base of the _scape_ swelled out into a spherical or other kindred
form[1526]; and often marked, as in the _Cicindelidæ_, with impressed
points: as it is the piece by which the antenna moves in its socket,
this form of a _rotula_ was doubtless given for its more ready motion
in all directions. This structure is principally conspicuous in the
_Coleoptera_ and _Hymenoptera_ Orders: in the others the base is not
so distinguished from the rest of the scape. If you carefully extract
the antennæ of a beetle, say a _Copris_ or _Lamia_, and examine its
base or bottom, you will find that it is open for the transmission
of muscles and nerves; that in its upper margin it has a deep notch
or sinus, on each side of which is a smaller notch; and that all
round the margin, which is very lubricous, a membranous ligament is
attached, by which it was affixed in the torulus. Its articulation,
therefore, seems of a mixed kind, like that of most other organs and
parts of insects, partaking of the ligamentous, ginglymous, and ball
and socket. In the _Orthoptera_, _Hemiptera_, &c. the articulation
seems more purely ligamentous.

With regard to their _substance_--these organs are regulated, in some
degree, by the nature of the integument of the animal of which they
are appendages; in the softer insects being of a softer substance than
they are in hard ones. The vertex of the joints, where they receive the
succeeding one, appears in many cases to be softer than the rest of
it, and especially towards the apex, often papillose. The antennæ are
generally opaque; but in _Nebria complanata_, a beetle common on the
sea-coast in Wales and Lincolnshire, they are semitransparent.

The _situation_ of antennæ must next be considered. In this respect
it seems necessary that they should be so situated as to be under
the direction of the eyes: for if you examine ten thousand insects
(except, as was before observed[1527], where there are _four_ eyes),
you will not find one in which these organs are situated either above
or immediately behind them; their station being always either somewhere
in the space between the eyes or that below them. In _Ptinus_ F. they
are placed near the vertex; but in _Gibbium_, which is so nearly
related to that destructive genus[1528], they are beneath them. In many
_Melittæ_ K. they are in the middle of the space between the eyes; and
in many other _Hymenoptera_ and _Coleoptera_ (_Staphylinus_ &c.), in
the anterior part of it. In many Lamellicorn genera (except in some
_Acridæ_, as _A. viridissima_) as _Melolontha_, _Cetonia_, _Lucanus_,
&c. they may be regarded as planted in the lower surface of the cheek
before the eyes; but in _Copris_ &c., in which they are inserted
further under the shield of the head, they are properly in the _prone_
surface of the _front_. In the Capricorn-beetles (_Cerambyx_ L.) and
_Cnodalon_ F. they may be termed _inocular_, or placed in a sinus of
the eye; in the former tribe in its _interior_, and in the latter its
_anterior_ side. In the Rhynchophorous or rostrum-bearing beetles
(_Curculio_ L.) they vary in their situation. Thus in _Macrocephalus_
Oliv. they are inserted at its apex; in _Anthribus_ in its middle,
and in _Calandra_ at its base[1529]. In the water-scorpions (_Nepa_,
_Belostoma_, &c.) they may be called _extraocular_, being placed
under the head in its prone part, outside the eyes[1530]. In _Nirmus
Fringillæ_, a kind of bird-louse, they appear to be _oral_, being
situated, according to De Geer, under the head near the mouth, at a
great distance from the eyes[1531].

In their _proportions_, both as to length and thickness, antennæ vary
extremely. Thus sometimes they are very short--much shorter than
the head; as in the aquatic beetles _Gyrinus_, _Parnus_, and the
water-scorpion; and some land-beetles, as _Anthrenus_, &c. At other
times they far exceed the length of the insect: the males of many
Capricorn-beetles are so distinguished. In that of _Lamia ædilis_
they are more than _four_ times as long as the body; and every
intermediate length between these two may be found amongst them.
They vary also greatly in _thickness_: in _Paussus_, whose antennæ
emit light in the night[1532], and _Cerapterus_, they are nearly as
thick,--at least their knob, which forms the chief part of them,--as
the body of the insect[1533]; while in _Mantis_, _Acrida_ K. and
_Psocus_, they are as slender as a hair. The antennæ in many of the
_Prioni_, especially in _P. imbricornis_, are thick from base to tip;
while in other Capricorn-beetles they are quite the reverse.

It will not be necessary to enlarge here upon the general _form_
of these organs: I shall therefore only notice the two principal
divisions of them in this respect.--Antennæ, regard being had to
one of their uses, may be divided into two sections, distinguished
by forms extremely different: those, namely, that are employed by
insects as _tactors_ to explore their way, and those that cannot be so
employed. The great majority are of the former kind; but those that
may be denominated _setigerous_,--as the antennæ of the _Libellulina_,
_Ephemerina_, of the Homopterous _Hemiptera_, and of many _Diptera_,
the last joint of which terminates in a bristle, or is furnished
with a lateral one, and of some gnats that have short feathered
antennæ,--appear not fitted to be used as tactors to explore by touch,
and form the latter description. This difference in these organs, as
I shall have occasion to prove more at large hereafter, furnishes a
strong presumption that their _primary_ function is not _touch_. Were
this the case, it would be common to them all.

As to their _structure_, antennæ consist in general of a number
of tubular joints; each of which having separate motion, the
animal is thereby enabled to give them every flexure necessary for
its purposes. The _scape_, or first joint, by means of the bulb
inosculates in the _torulus_, or is suspended to it; and the others,
sometimes by a similar, though less pronounced knob at their base,
inosculate in the preceding one; but in some cases the inosculation
seems not so perfect, the joints being simply suspended by ligament.
In pectinated or lamellated antennæ, the branch is usually a lateral
process of the joint from which it issues; but in _Phengodes_
(_Lampyris plumosa_ L.) its involute plumose branches appear to
articulate with the apex of each joint[1534]. I have a specimen of
one of the _Cleridæ_, of a genus undescribed, in which each branch
is forked. In some tribes of the Capricorn-beetles (_Stenocorus_,
&c.) the antennæ are often armed at their apex with spines, sometimes
on the upper side and sometimes below. In some aquatic beetles
(_Gyrinus_, _Parnus_) they are furnished with an auricle at their
base, which, like the lid of a box, shuts them in when unemployed,
and protects them from the water[1535].

The portions into which antennæ may in general be considered as
divided, have been sufficiently explained to you above; but it may
not be amiss to add here a few words on the principal variations in
their structure that I have had an opportunity of observing. The
_scapus_[1536] or first joint, which includes the _bulbus_, is usually
the most conspicuous joint in the antenna (exclusive, I mean, of the