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].