antennæ of insects, I shall endeavour to discover whether there is
any part in the higher animals to which they may be deemed to exhibit
any analogy. And here I must refer you to what I have said on a
former occasion upon the present subject; where I made it evident, I
hope, that the great bulk of the parts and organs of insects, in this
particular differing from the majority of Invertebrates, are, some
in one respect, some in another, and some in many, really analogous
to those of the higher animals[1036]; and that a great many of them,
though varying in their structure, have the same functions. Thus
the analogues of the _eyes_ of Vertebrates are for _seeing_; of the
_jaws_ for _masticating_; of the _lips_ for _closing_ the _mouth_; of
the _legs_ for _walking_, &c. We have seen also very recently, that
a similar analogy, more or less strongly marked, holds also in their
internal organs[1037]; so that it may be safely affirmed, that if all
the invertebrate insects, though gifted with numerous peculiarities,
present the most striking picture of those animals that have an
internal skeleton, and more particularly of the _Mammalia_,--we may
assume it as a probability, the above circumstances being allowed
their due weight, that where facts do not prove the contrary, the
function of analogous organs is more or less synonymous, though
perhaps the structure and _modus operandi_ may be different.
In the letter lately referred to, I observed that the antennæ of
insects are analogous to _ears_ in Vertebrates[1038]. Their _number_
corresponds; they also stand out from the head; and what has
weighed most with me, unless they are allowed as such, no other
organ can have any pretension to be considered as representing the
ear. If we reflect, that in every other part and organ, the head of
insects has an analogy to that of _Mammalia_, we must regard it as
improbable that these prominent organs should not also have their
representative. Admitting then that they are the analogues of ears,
it will follow, not as demonstratively certain, but as probable,
that their _primary_ function may be something related to hearing.
I do not say direct _hearing_, or that the vibrations of sound are
communicated to the sensorium by a complex structure analogous to
that of the internal ear in _Mammalia_--but something _related_
to hearing. I conceive that antennæ, by a peculiar structure, may
collect notices from the atmosphere, receive pulses or vibrations,
and communicate them to the sensorium, which, though not precisely to
be called hearing, may answer the same purpose. From the _compound_
eyes that most of them have, the sense of seeing in insects must
be very different from what it is in vertebrate animals; and yet
we do not hesitate to call it _sight_: but since antennæ, as we
shall see, apparently convey a _mixed_ sensation, I shall have
no objection, admitting it as their primary function, to call it
after Lehmann _Aëroscepsy_[1039]. I lately related some instances
of _sound_ producing an effect on the _antennæ_ of insects: I will
now mention another that I observed, still more remarkable. A
little moth was reposing upon my window; I made a quiet, not loud,
but distinct noise: the antenna nearest to me immediately moved
towards me. I repeated the noise at least a dozen times, and it
was followed every time by the same motion of that organ; till at
length the insect being alarmed became more agitated and violent
in its motions. In this instance it could not be _touch_; since
the antenna was not applied to a surface, but directed towards the
quarter from which the sound came, as if to listen. Bonsdorf made
similar observations, to which Lehmann seems not disposed to allow
their proper weight[1040]. It has been used as an argument to prove
that antennæ are primarily _tactors_, or instruments of _touch_,
that _Fœnus Jaculator_, before it inserts its ovipositor, plunges
its _antennæ_ into the hole forming the nidus of the bee, to the
grub of which it commits its egg[1041]. But had those who used this
argument _measured_ the antennæ and the ovipositor of this ichneumon,
they would have discovered that the latter is thrice the length of
the former: and as these insects generally insert it so that even
part of the abdomen enters the hole, it is clear that the antenna
cannot _touch_ the larva; its object therefore cannot be to explore
by that sense. Others suppose that by these organs it _scents_ out
the destined nidus for its eggs; but Lehmann has satisfactorily
proved that they are not _olfactory_ organs. We can therefore only
suppose, either that by means of its antennæ it _hears_ a slight
noise produced by the latent grub, perhaps by the action of its
mandibles; or else that by its motions it generates a _motion_ in
the atmosphere of its habitation, which striking upon the antennæ
of the _Fœnus_, are by them communicated to its sensory. A similar
disproportion is observable between the antennæ and ovipositor of
_Pimpla Manifestator_, before signalized[1042]. Bees, when collecting
honey and pollen, first insert the organs in question into the
flowers which they visit; but, as I have more than once observed,
they merely insert the _tip_ of them. If anthers are bursting, or the
nectar is exuding, these processes probably are attended by a slight
noise, or motion of the air within the blossom, which, as in the last
case, affects, without immediate contact, the exploring organs.
If the _structure_ of antennæ be taken into consideration, it will
furnish us with additional reasons in favour of the above hypothesis,
with regard to their primary function. We shall find that these
organs, in most of those insects which take their food by suction,
are usually less gifted with powers of motion, than they are in
the mandibulate tribes; so that in the majority of the Homopterous
_Hemiptera_ and _Diptera_, as is generally acknowledged, they cannot
be used for _touch_. Under this view, they may be divided into
_active_ antennæ and _passive_ antennæ: of the former, the _most_
active and versatile are those of the _Hymenoptera_. By means of
them, as was before observed[1043], their gregarious tribes hold
converse, and make _inquiry_--frequently without _contact_--in the
pursuit and discharge, if I may so speak, of the various duties
devolved upon them by PROVIDENCE. Amongst active antennæ, some are
much more _complex_ in their structure than others--a circumstance
which is often characteristic of the _male_ insect[1044]: but if
we examine such antennæ, we shall find that their most _sensitive_
parts cannot come in _contact_ with the earth or other bodies for
exploring their way; but having thus a greater surface exposed to
the action of the atmosphere, they have more points to receive
vibrations, or any pulses or other notices communicated to it.
It is thus, probably, that in their flights, when they approach
within a certain distance, they discover the station of the other
sex. Even the plumose antennæ of male gnats may in some respects
thus be acted upon. In the Lamellicorn beetles, the knob of these
organs in both sexes consists of laminæ, the external ones on their
outside, of a corneous substance; while their internal surface, and
the inner laminæ--which are included between them, as an oyster
between the valves of its shell--are covered with nervous papillæ.
If you examine the proceedings of one of these little animals, you
will find before it moves from a state of repose that its antennæ
emerge, and the laminæ diverge from each other; but that it does
not apply them to _surfaces_ to explore its way, but merely keeps
them _open_ to receive notices from the atmosphere. Even _simple_
antennæ are often employed in this way, as well as for touch. I once
noticed a species of _Leptocerus_, a trichopterous genus, in which
these organs are very long, that was perched upon a blade of grass;
its antennæ vibrated, and it kept moving them from side to side in
the air, as if thus by aëroscepsy it was inquiring what was passing
around it. Dr. Wollaston has an observation bearing so precisely
upon this question, and in general so extremely similar to what is
here advanced, that I must copy it for your consideration. "Since
there is nothing in the constitution of the atmosphere," says he,
"to prevent vibrations much more frequent than any of which we are
conscious, we may imagine that animals like the _Grylli_, whose
powers appear to commence nearly where ours terminate, may have the
faculty of hearing still sharper sounds, which at present we do not
know to exist; and that there may be other insects, hearing nothing
in common with us, but endued with a power of exciting, and a sense
that perceives, vibrations indeed of the same nature as those which
constitute our ordinary sounds, but so remote, that the animals
who perceive them may be said _to possess another sense, agreeing
with our own solely in the medium by which it is excited_, and
possibly wholly unaffected by these slower vibrations of which we are
sensible[1045]." That insects, however, hear nothing in common with
us, is contrary to fact; at least with respect to numbers of them.
They hear our sounds, and we theirs; but their hearing or analogous
sense is much nicer than ours, collecting the slightest vibratiuncle
imparted by other insects, &c. to the air. In inquiring how this is
done, it may be asked--How know we that every joint of some antennæ
is not an acoustic organ, in a certain sense distinct from the rest?
We see that the eyes of insects are usually compound, and consist
of numerous distinct lenses;--why may not their external ears or
their analogues be also multiplied, so as to enable them with more
certainty to collect those fine vibrations that we know reach their
sensory, though they produce no effect upon our grosser organs? I
propose this merely as conjecture, that you may think it over, and
reject or adopt it, in proportion as it appears to you reasonable or
the contrary; and in the hope that some anatomist of insects, who, to
the sagacity and depth of a Cuvier and a Savigny adds the hand and
eye of a Lyonet, may give to the world the results of a more minute
dissection and fuller investigation of the antennæ of these animals,
than has yet been undertaken.
But besides receiving notices from the atmosphere, of sounds, and
of the approach or proximity of other insects, &c., the antennæ are
probably the organs by which insects can discover alterations in its
state, and foretel by certain prognostics when a change of weather
is approaching. Bees possess this faculty to an admirable degree.
When engaged in their daily labours, if a shower is approaching,
though we can discern no signs of it, they foresee it, and return
suddenly to their hives. If they wander far from home, and do not
return till late in the evening, it is a prognostic to be depended
upon, that the following day will be fine: but if they remain near
their habitations, and are seen frequently going and returning,
although no other indication of wet should be discoverable, clouds
will soon arise and rain come on. Ants also are observed to be
excellently gifted in this respect: though they daily bring out their
larvæ to sun them, they are never overtaken by sudden showers[1046].
Previously to rain, as you well know, numberless insects seek
the house; then the _Stomoxys calcitrans_, leaving more ignoble
prey, attacks us in our apartments, and interrupts our studies and
meditations[1047]. The insects of prey also foresee the approach of
wet weather, and the access of flies, &c. to places of shelter. Then
the spiders issue from their lurking-places, and the ground-beetles
in the evening run about our houses. Passive antennæ, which are
usually furnished with a terminal or lateral bristle, and plumose and
pectinated ones, seem calculated for the action of the _electric_ and
other fluids dispersed in the atmosphere, which in certain states
and proportions may certainly indicate the approach of a tempest,
or of showers, or a rainy season, and may so affect these organs as
to enable the insect to make a sure prognostic of any approaching
change: and we know of no other organ that is so likely to have
this power. I say _electric_ fluid, because when the atmosphere is
in a highly electrified state, and a tempest is approaching, is the
time when insects are usually most abundant in the air, especially
towards the evening; and many species may then be taken, which are
not at other times to be met with: but before the storm comes on, all
disappear, and you will scarcely see a single individual upon the
wing. This seems to indicate that insects are particularly excited
by electricity[1048].--But upon this head I wish to make no positive
assertion, I only suggest the probability of the opinion[1049].
From all that has been said, I think you will be disposed to admit
that the primary and most universal function of the antennæ is to
be the organs of a sense, if not the same, at least analogous to
_hearing_, and answering the same end; something perhaps between it
and touch. In some, however, as has been found in the _Crustacea_, an
organ of hearing, in the ordinary sense, may exist at the base of the
antennæ, which may act the part in some measure of the external ear,
and collect and transmit the sound to such organ[1050].
That numerous antennæ, as a _secondary_ function, explore by _touch_,
is admitted on all hands, and therefore I need not enlarge further
upon this point; but shall proceed to inquire whether insects do not
possess some other peculiar organs that are particularly appropriated
to this sense. First, however, I must make some _general_
observations upon it. Of all our senses, _touch_ is the only one
that is not _confined_ to particular organs, but dispersed over the
whole body: insects, however, from the indurated crust with which
they are often covered, feel sensibly, it is probable, only in those
parts where the nerves are exposed, by being covered with a thinner
epidermis, to external action. Not that they cannot feel at all in
their covered parts; for as we feel sufficiently for walking, though
our feet are covered by the thick sole of a boot or shoe, so insects
feel sufficiently through the crust of their legs for all purposes
of motion. Besides, the points that are covered by a thinner cuticle
are often numerous; so that touch, at least in a _passive_ sense,
may be pretty generally dispersed over their bodies; but _active_ or
exploring touch is confined to a few organs, as the _antennæ_, the
_palpi_, and the _arms_. The two last I shall now discuss.
Various opinions have been started concerning the use of the _palpi_.
Bonsdorf thought that they were organs of _smell_; Knoch, that this
sense was confined to the _maxillary_ ones, and that the _labial_
ones were appropriated to _taste_[1051]: but the most early idea, and
that from which they derive their present name of palpi (_feelers_),
is, that they are organs of active _touch_; and this seems to me the
most correct and likely opinion. Cuvier, himself a host, has embraced
this side of the question[1052], and Lehmann also admits it[1053].
The following observations tend to confirm this opinion. The palpi of
numerous insects when they walk, are frequently, or rather without
intermission, applied to the surface on which they are moving--this
you may easily see by placing one upon your hand; which seems to
indicate that they are _feelers_. In the _Araneidæ_ they are used as
_legs_; and by the males at least, as _exciting_ if they be not really
_genital_ organs[1054]. In the _Scorpionidæ_ they answer the purpose
of _hands_: besides being usually much shorter than antennæ, they
are better calculated to assist an insect in threading the dark and
tortuous labyrinths through which it has often to grope its way, and
where antennæ cannot be employed. I have noticed that _Hydrophili_--in
which genus the _palpi_ are longer than the antennæ--when they swim,
have their antennæ folded; while the former are stretched out in front,
as exploring before them. As these are attached to the under-jaws and
under-lip, we may suppose they are particularly useful to insects in
taking their food; and upon this occasion I have often observed that
they are remarkably active. I have seen _Byturus tomentosus_, a beetle
which feeds upon pollen, employ them in opening anthers; and the
maxillary pair appear to me to assist the maxillæ in holding the food,
while the mandibles are at work upon it.
The _arms_ or fore-legs of some insects are also organs of _active_
touch, being used, as we have seen, for cleaning the head, digging,
repairing their dwellings, and the like[1055]. By the _Ephemeræ_,
which have very short antennæ, the fore-legs, when they fly, are
extended before the head, parallel with each other and quite
united--probably to assist in cutting the air. The _Trichoptera_ use
their antennæ for the same purpose.
* * * * *
Another sense of which the organ seems uncertain is that of _smelling_,
and various and conflicting opinions have been circulated concerning
it. Christian thought that insects smell _distant_ objects with their
_antennæ_, and _near_ ones with their _palpi_[1056]. Comparetti has
a most singular opinion. He supposes in different tribes of insects
that different parts are organs of smell: in the _Lamellicorns_ he
conjectures the seat of this sense to reside in the _knob_ of the
_antennæ_; in the _Lepidoptera_ in the _antlia_; and in some _Diptera_
and _Orthoptera_ in certain _frontal cells_[1057]. At first sight, one
of the most reasonable opinions seems to be that of Baster, adopted by
Lehmann, and which has received the sanction of Cuvier[1058],--that
the _spiracles_ are organs of smell as well as of respiration. Lehmann
has adduced several arguments in support of this opinion. Because we
both respire and smell with our nostrils, he concludes that neither
the antennæ nor any other part of the head of insects can serve for
_smell_, since they are not the seat also of _respiration_; and that
there can be no smell where the air is not inspired[1059]. Again,
because nerves from the ganglions of the spinal chord terminate in
bronchiæ near the spiracles, they must be for receiving scents from
those openings. Though it was necessary, in the higher animals,
that the organ of scent should be near the mouth, because they are
larger than their food; yet the reverse of this being the case with
insects, which often even reside in what they eat, it is to them of no
importance where their sense of smelling resides[1060]. By exposing
antennæ, by means of an orifice in a glass vessel, to the action of
stimulant odours, they appeared quite insensible to it: but he does not
name the result of any experiment in which he exposed the _mouth_ to
this action; nor at all distinctly how the insect was affected when the
spiracles were exposed to it[1061].
But though some of these arguments appear weighty, there are others,
I think, that will more than counterbalance them, making it probable
that the seat of this sense is in the head, either in its ordinary
station at the extremity of what I call the _nose_, between it and
the upper-lip, or under those parts. That the nose corresponds
with the so-named part in _Mammalia_, both from its situation and
often from its form, must be evident to every one who looks at an
insect[1062]; and when we further consider the connexion that obtains
between the senses of smell and taste, how necessary it is that the
seat of the one should be near that of the other, and that it really
is so in all animals in which we certainly know its organ[1063]; we
shall feel convinced that the argument from analogy is wholly in
favour of the nose, and may thence consider it as probable that the
sense in question does reside there. Lehmann seems to be of opinion,
because an insect is usually smaller than what it feeds upon, that
it makes no difference whether it smells with its _head_ or with its
_tail_: but one would think that a _flying_ insect would be more
readily directed to its object by smelling with the _anterior_ part
of the body than with the _posterior_; and that a _feeding_ one
would also find it more convenient in selecting its food. As to the
argument,--that _smell_ must be the _necessary_ concomitant of the
_respiratory_ openings, and that there can be no smell where the
_air_ is not inspired,--this seems asserting more than our knowledge
of these animals will warrant: for the organs of the _other_ senses,
though the senses themselves seem analogous, are so different in
their structure, and often in the mode in which they receive the
impressions from external objects, that analogy would lead us to
expect a difference of this kind also in the sense of smell. Besides,
smell does not _invariably_ accompany respiratory organs even in the
higher animals,--for we _breathe_ with our _mouths_, but do not smell
with them. Cuvier says that the _internal_ membrane of the tracheæ
being soft and moist, appears calculated to receive scents[1064]. But
here his memory failed him; for it is the _external_ membrane alone
that answers this description; the _internal_ consisting of a spiral
elastic thread, and seeming not at all fitted to receive impressions,
but merely to convey the air[1065]. That nerves penetrate to the
bronchiæ, does not necessarily imply that they are connected with the
sense in question, since this may be to act upon the muscles which
are every where distributed.
I shall now state some facts that seem to prove that scents are
received by some organ in the vicinity of the _mouth_, and probably
connected with the _nose_. M. P. Huber, desirous of ascertaining
the seat of smell in _bees_, tried the following experiments with
that view. These animals, of all ill scents, abominate most that of
the oil of turpentine. He presented successively to all the points
of a bee's body, a hair-pencil saturated with it: but whether he
presented it to the abdomen, the trunk, or the head, the animal
equally disregarded it. Next, using a very fine hair-pencil, while
the bee had extended its proboscis, he presented the pencil to it,
to the eyes and antennæ, without producing any effect; but when he
pointed it _near the cavity of the mouth, above the insertion of
the proboscis_, the creature started back in an instant, quitted
its food, clapped its wings, and walked about in great agitation,
and would have taken flight if the pencil had not been removed. On
this, it began to eat again; but on the experiment being repeated,
showed similar signs of discomposure: oil of marjoram produced the
same effect, but more promptly and certainly. Bees not engaged in
_feeding_ appeared more sensible of the impression of this odour, and
at a greater distance; but those engaged in absorbing honey might
be touched in every other part without being disturbed. He seized
several of them, forced them to unfold their proboscis, and then
stopped their mouth with paste. When this was become sufficiently
dry to prevent their getting rid of it, he restored to them their
liberty: they appeared not incommoded by being thus gagged, but moved
and respired as readily as their companions. He then tempted them
with honey, and presented to them near the mouth, oil of turpentine,
and other odours that they usually have an aversion to; but all
produced no sensible effect upon them, and they even walked upon the
pencils saturated with them[1066].