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
_capitulum_, in those in which that organ terminates in a knob),
it being thicker and often longer than the succeeding ones. In the
Capricorn and Darkling beetles, indeed (_Cerambyx_ and _Tenebrio_ L.),
the third joint is the longest, but the scape is still the thickest;
and in the stag-beetles (_Lucanus_ L.), many of the weevil tribes
(_Curculio_ L.), and those of the bees (_Apis_ L.), except in the
males, it is as long nearly as the remainder of the antennæ, which
forms an angle with it. In shape it is generally somewhat curved and
subclavate, or increasing in size from the base to the summit; but
it is sometimes straight and filiform, at others oblong or square,
at others again triangular, in several instances three-sided: in one
(_Cetonia cruenta_ F. _Genuchus_ K.) it is, as it were, broken, the
upper part forming nearly a right angle with the lower; in _Cerocoma
Schæfferi_ it is foliaceous; and it is occasionally suborbicular: and
probably many other forms might be enumerated.
The _Pedicellus_[1537] is the _second_, and may be deemed the _least
conspicuous_ joint of the antennæ. Though more slender than the scape,
it is generally thicker than that which immediately follows it. In
broken antennæ it is the hinge or pivot on which the _clavola_ or upper
member turns: it is usually very short, campanulate or bell-shaped, or
obconical; but in a species of bug (_Tetyra_, from New Holland--_T.
pedicellata_ Kirb. MS.) it is nearly as long as all the rest of
the joints taken together. In those species of _Lycus_, a genus of
beetles related to the glow-worm, that have flattened antennæ (as _L.
reticulatus_, _fasciatus_, &c.), this joint is almost received into the
socket of the scape, so that their antennæ appear at first to have only
_ten_ joints, but in those which have those organs filiform (as _L.
minutus_, _Aurora_, &c.) it is more conspicuous.
The _Clavola_[1538], or remaining joints of the antennæ taken
together, constitutes the principal part of the organ, which,
especially at its extremity, exercises its functions of touch, or
any other sense. The principal variations, as to form and structure,
that occur in this part will be mentioned in another place. I shall
only here observe, that in many instances the first joint of this
part is longer than the rest; but in _Tetyra pedicellata_ just
mentioned, it is by far the shortest, and shaped like the pedicel
of most insects. In the _Libellulina_, the Homopterous _Hemiptera_,
and those flies whose antennæ terminate in a bristle, the clavolet
is represented by the bristle. But in the flies which have a lateral
bristle, on the last joint, and those with triarticulate antennæ that
have no bristle, the terminal joint represents it. The clavolet often
terminates in a knob, or in several joints thicker than that which
precedes them. This varies greatly, not only in its form, but also
in the number of joints of which it is composed. Thus in _Paussus_,
_Platypus_, and many _Calandræ_, it consists of only a _single_
joint[1539]; in _Anthrenus_, _Ditoma_, &c. of _two_; in _Nitidula_,
_Geotrupes_, &c. of _three_[1540]; in _Tetratoma_, the _Silphidæ_,
of _four_[1541]; of _five_ in _Scaphidium_[1542]; of _six_ in
one species of _Languria_, of _seven_ in the common cockchafer
(_Melolontha vulgaris_[1543]); of _eight_ in _Diaperis Boleti_, in
which the whole clavolet forms the club[1544]; of _nine_ in _Oenas_;
and _ten_ in _Cerapterus_[1545]. All the above, you will observe,
are _beetles_. In the other orders there are _eleven_ joints in the
knob of some butterflies; _twelve_ in that of _Ascalaphus_[1546] and
_Myrmeleon_; and lastly, _fourteen_ in _Trachelus_[1547].
Under _structure_ also, the _number_ of joints of which antennæ in
general consist, should be considered. If you examine the insects
belonging to the different orders, you will find remarkable variations
in this respect. Let us run through them:--In the _Coleoptera_ the
natural number of joints is _eleven_; but this rule is not without
many exceptions. Thus, many have _fewer_ than the prescribed number:
_Paussus_ has only _two_[1548], _Claviger_ and _Platypus_ five,
_Dorcatoma_ and _Calandra_ eight[1549], _Geniates_ K. and _Phanæus_
MacLeay nine[1550], and lastly _Melolontha ten_[1551]. Others, again,
have _more_ than eleven joints: _Cebrio grandis_, _Chrysomela stolida_,
some _Saperdæ_, and several others, have _twelve_. In _Prionus
imbricornis_ the female has _nineteen_, and the male _twenty_[1552].
_Rhipicera marginata_ has _thirty-two_; and in a New Holland species
of this genus I counted _thirty-eight_. In the _Orthoptera_ I can
trace no general law in this respect. In _Locusta_ Leach in some
species you may count _fourteen_ joints, in others _sixteen_, and in
others _twenty-five_. In one, which appears to be a pupa, I found
only _thirteen_. In _Mantis_ they exceed _thirty_; but in _Blatta_,
from between _thirty_ and _forty_, they reach nearly _one hundred
and fifty_; often varying in number in different individuals of the
same species. The order _Hemiptera_ exhibits two peculiar types of
antennæ, which, with some exceptions, distinguish the two natural
sections into which M. Latreille has judiciously divided it. In the
_Heteropterous_ section they are _without_ a bristle at their end; and
in the _Homopterous_ one, with the exception of _Aphis_, _Thrips_,
&c. they _have_ one. In the genera of both these tribes, the number
of joints varies in these organs. Thus, exclusive of the seta, in
_Flata_ and _Cixius_ there are only _two_ joints; in _Galgulus_,
_Fulgora_, and _Cercopis_, there are _three_; in _Lygæus_, _Coreus_,
&c. there are _four_; in _Tetyra_, _Pentatoma_, _Tettigonia_, there
are _five_[1554]; in _Aleyrodes_ there are _six_; in _Aphis seven_; in
_Thrips eight_; in _Psylla ten_, the last of which is terminated by
two bristles[1555]; and in _Coccus eleven_. The _Neuroptera_ order,
as it stands at present, is regulated by no general rule with regard
to the number of joints in the antennæ of the insects that compose
it. Several types of form in these organs distinguish its discordant
tribes. The _first_ is that of the _Ephemeræ_, in which the antennæ
consist of two short joints, crowned by a short, tapering, _unjointed_
bristle. The _second_ is that of the _Libellulina_, similar to the
above, but with a _jointed_ bristle. The _third_ is that of _Psocus_,
in which the antenna has two short thick joints at the base, terminated
by a long filiform bristle, consisting of seven or eight joints, and
finer than a hair. Perhaps these three may be regarded as belonging to
a common type. The _fourth_ type is presented by the short filiform
antennæ of _Termes_; the _fifth_ by the setaceous ones of _Corydalis_,
_Hemerobius_, &c.; and the _sixth_ and last by the clavate and
capitate ones of _Myrmeleon_ and _Ascalaphus_. In the _Lepidoptera_
and _Trichoptera_ orders the antennæ, though varying in their general
form in the three tribes of which Linné formed his genera _Papilio_,
_Sphinx_, and _Phalæna_, with the exception of _Hepialus_, in which
the joints are few, are always _multiarticulate_:--we will therefore,
without further delay, proceed to the _Hymenoptera_. In Latreille's
tribe _Aculeata_ the general rule is, that the females shall have
_twelve_ joints and the males _thirteen_. In his _Ichneumonides_
the law seems to be, that the antennæ shall be multiarticulate
and setaceous; but in most of the other tribes of the order, even
those that in other respects are most nearly related,--as in his
_Tenthredinetæ_,--the number of joints of these organs varies without
end. Thus in _Hylotoma_ there are only _three_ joints[1556]; in _Cimbex
læta_[1557] _five_; in _C. axillaris_ and _Perga_ Leach[1558], six:
and so on to twenty-five or more[1559]. The same fluctuation in this
respect runs throughout the rest of the order. In the _Diptera_ there
are two general types of antennæ:--those of the _Tipulariæ_ Latr.,
consisting usually of from _fourteen_ to _sixteen_ joints, in the
males often resembling beautiful plumes; and those of the remainder of
the order, in which they do not exceed _three_ joints[1560]: though
the last, or _patella_, is often further divided into obsolete or
indistinct ones[1561]. These antennæ may be further subdivided into
_filatæ_ and _aristatæ_, or those without and those with a bristle,
either lateral or terminal.
The _clothing_ of antennæ also merits attention, since it is often
not a little remarkable. By clothing I understand the _down_ or
_hairs_ of every kind with which they are either generally or
partially covered. A great number of filiform and setaceous antennæ
of Predaceous beetles (_Cicindela_ L., _Carabus_ L.) have the first
two, three, or four joints naked, and the rest covered with a fine
down. In insects that have a knob at the end of these organs, whether
lamellated or perfoliate, this down is often confined to it, or to its
intermediate joints, and seems intermixed with nervous papillæ. These
are particularly visible in the flabellate antennæ of _Rhipicera_,
_Lampyris Latreillii_[1562], _Elater flabellicornis_[1563], &c.
covering both surfaces of the processes of the joints. In some male
bees these papillæ are inclosed in hexagonal spaces into which the
antennæ are marked out[1564]. It is to be observed, that in many
antennæ the joints of the clavolet have one or two bristles or more
at their apex, one above perhaps, and one below; the lower angle in
those of the serrated antennæ of _Elater_ is usually so furnished, and
sometimes the upper. In many Capricorn-beetles and various insects the
antennæ are clothed, instead of down, with stiffish hairs or short
bristles. Other insects have these organs, at least the clavolet,
beset with longer hairs standing out from them on all sides: of this
kind are those of a singular beetle (_Sarrotrium muticum_) sometimes
found in this country[1565]. Again, there are some that have only
their underside bearded with longer hairs; as _Lamia curculionoides_,
_speculifera_ K., and other Capricorns[1566]. In another of this tribe,
_Saperda hirsuticornis_, the three intermediate joints are ornamented
with branches of long black hairs, which give them an elegant and
feathery appearance[1567]. In _Callichroma alpina_ the apex of the
slate-coloured joints of its antennæ is bearded with black hairs. In
_Lamia reticulata_, and _Saperda fasciculata_ and _plumigera_, all
also Capricorns, a single bunch of hairs, resembling the brush of a
bottle-cleaner, signalizes the middle of the antenna[1568]: in _Saperda
scopulicornis_ K. this is star-shaped[1569]. Sometimes the _scape_ is
externally bearded, as in _Trox_, a beetle found in horns and bones;
and in many other Lamellicorns[1570]. In this last tribe the two
exterior leaves of the knob of the antennæ are often set with short
bristles[1571]; and in a minute beetle called by De Geer _Dermestes
atomarius_, the hairs of this part are said to form a brush[1572].
When insects, I mean more particularly _Coleoptera_, are about to
move from any station where they have been at rest, the first thing
they usually do, before they set a step, is to bring forward and
_expand_ their antennæ, which have either been carefully laid up
in a cavity fitted to receive them, or back upon the body: if they
terminate in a lamellated knob, they separate the lamellæ as far as
possible from each other; or if it is perfoliate, the joints of it
mutually recede. The object of this is evidently to collect notices
from the atmosphere, since the papillose part of these joints cannot
be applied to surfaces. When the animal begins to move, in many cases
the antennæ do the same, and continue their _motion_ till it stops
and returns to a state of repose. In the parasitic tribes of the
_Hymenoptera_ (_Ichneumon_ L.) they are kept in an almost constant
vibration. Many other insects move them in all directions without
any order or regularity; and others, when they elevate one depress
the other, and so proceed as if balancing themselves by means of
these organs like a rope-dancer. I have before stated to you how by
motions of their antennæ, ants and bees communicate their wants or
discoveries to each other, or make inquiry concerning any thing they
wish to know[1573]. But as I shall have occasion to make some further
remarks upon this subject, when the senses of insects are under
discussion, I shall for the present take my leave of it.
I shall conclude what I have to communicate to you relative to
the organs of which we are treating, with a few observations with
respect to their _station_ when the insect _reposes_. In the
Capricorn-beetles, _Eucera_ and other insects with _long_ antennæ,
they are merely turned back or on one side with no particular cavity
for their reception when unemployed, but probably the apex passes
under the body. In the Predaceous and Darkling beetles (_Carabus_
L., _Tenebrio_ L.) their station is usually under the sides of
the _prothorax_, and in the Tortoise beetles (_Cassida_), under
its anterior margin. In the Elastic beetles (_Elater_) they are
received into a groove between the under margin of that part and
the fore-breast (_antepectus_). In _Anthrenus_, when the animal
reposes or counterfeits death, the antennæ are concealed in a cavity
of the underside of the _prothorax_, at right angles with the
throat[1574]. In the kindred genus _Byrrhus_, another simulator of
death, a large cavity is excavated under the same part, to receive
both the forelegs and antennæ, a narrow space being left between
the angle of the _prothorax_ and fore-breast exactly admitting the
base of the latter, which are quite concealed under the former. In
_Cryptocephalus_ and _Chlamys_, kindred beetles, when at rest they
are withdrawn, except their scape and pedicel, with the head within
the cavity of the _prothorax_. In others they are turned under the
head, without any particular cavity for their reception; as in
many moths, _Apion_, &c. In most of the Lamellicorn beetles their
station is in the cavity formed by the eye and the throat, the knob
forming an angle with the rest of the antenna. In _Heterocerus_
they follow the contour of the eye[1575]. In _Brentus_, a genus
of weevils remarkably long and slender, they are turned back and
received by a slight longitudinal cavity of the rostrum; but in those
of this tribe (_Curculio_ L.) in which the clavolet forms an angle
with the long scape, this latter part, bending back, is laid up in
an oblique channel of that part; and the former, pointing in the
contrary direction, is folded upon it. In many flies (_Muscidæ_) a
vertical frontal cavity receives the antennæ, which point downwards
during repose[1576]. _Cryptocerus_, a very remarkable ant, has on
its head a singular square plate, the sides of which form a deep
longitudinal cavity: in this cavity the antennæ, quite concealed,
repose in safety. A cavity equally remarkable is exhibited by the
water-scorpions, particularly _Belostoma_, in which is a _very_ deep
kidney-shaped box, between the eye and throat, to receive and defend
its singular antennæ[1577]; which, when they are reposing, is closed
by the exterior harder joints, and from which it seems as if they
turned out, like a sentinel out of his box. In some aquatic genera
of beetles, as _Gyrinus_, _Parnus_, &c. they are withdrawn within
a lateral cavity of the same part, and are defended from the water
externally by the auricle at their base[1578]. The flabellated and
lamellated antennæ, previous to their being folded for repose, close
all their plates; which in action are as widely expanded as possible,
so as to form a knob; and in some the middle piece is entirely
concealed, as if in a box. In broken antennæ, or those in which the
clavolet forms an angle with the scape, the former is folded upon the
latter, with its point downwards.
II. _Subfacies._--Having dispatched the _Facies_, or _upper_ side of
the head, I am next to consider the _Subfacies_, or _under_ side:
but as the principal parts that occupy this side have been already
considered, I shall have no occasion to detain you long.