What a horrible place must this world appear when regarded according
to our ideas from an insect’s point of view! The air infested with
huge flying hungry dragons, whose gaping and snapping mouths are ever
intent upon swallowing the innocent creatures for whom, according to
the insect, if he were like us, a properly constructed world ought
to be exclusively adapted. The solid earth continually shaken by the
approaching tread of hideous giants—moving mountains—that crush out
precious lives at every footstep, an occasional draught of the blood of
these monsters, stolen at life-risk, affording but poor compensation
for such fatal persecution.
Let us hope that the little victims are less like ourselves than the
doings of ants and bees might lead us to suppose; that their mental
anxieties are not proportionate to the optical vigilance indicated by
the four thousand eye-lenses of the common house-fly, the seventeen
thousand of the cabbage butterfly and the wide-awake dragon-fly, or
the twenty-five thousand possessed by certain species of still more
vigilant beetles.
Each of these little eyes has its own cornea, its lens, and a curious
six-sided, transparent prism, at the back of which is a special retina
spreading out from a branch of the main optic nerve, which, in the
cockchafer and some other creatures, is half as large as the brain. If
each of these lenses forms a separate picture of each object rather
than a single mosaic picture, as some anatomists suppose, what an awful
army of cruel giants must the cockchafer behold when he is captured by
a schoolboy!
The insect must see a whole world of wonders of which we know little
or nothing. True, we have microscopes, with which we can see one thing
at a time if carefully laid upon the stage; but what is the finest
instrument that Ross can produce compared to that with twenty-five
thousand object-glasses, all of them probably achromatic, and each one
a living instrument, with its own nerve-branch supplying a separate
sensation? To creatures thus endowed with microscopic vision, a cloud
of sandy dust must appear like an avalanche of massive rock-fragments,
and everything else proportionally monstrous.
One of the many delusions engendered by our human self-conceit and
habit of considering the world as only such as we know it from our
human point of view, is that of supposing human intelligence to be
the only kind of intelligence in existence. The fact is, that what we
call the lower animals have special intelligence of their own as far
transcending our intelligence as our peculiar reasoning intelligence
exceeds theirs. We are as incapable of following the track of a friend
by the smell of his footsteps as a dog is of writing a metaphysical
treatise.
So with insects. They are probably acquainted with a whole world of
physical facts of which we are utterly ignorant. Our auditory apparatus
supplies us with a knowledge of sounds. What are these sounds? They
are vibrations of matter which are capable of producing corresponding
or sympathetic vibrations of the drums of our ears or the bones of our
skull. When we carefully examine the subject, and count the number
of vibrations that produce our world of sounds of varying pitch, we
find that the human ear can only respond to a limited range of such
vibrations. If they exceed three thousand per second, the sound becomes
too shrill for average people to hear it, though some exceptional ears
can take up pulsations or waves that succeed each other more rapidly
than this.
Reasoning from the analogy of stretched strings and membranes, and of
air vibrating in tubes, etc., we are justified in concluding that the
smaller the drum or the tube the higher will be the note it produces
when agitated, and the smaller and the more rapid the aerial wave
to which it will respond. The drums of insect ears, and the tubes,
etc., connected with them, are so minute that their world of sounds
probably begins where ours ceases; that the sound which appears to
us as continuous is to them a series of separated blows, just as
vibrations of ten to twelve per second appear to us. We begin to hear
such vibrations as continuous sounds when they amount to about thirty
per second. The insect’s continuous sound probably begins beyond three
thousand. The blue-bottle may thus enjoy a whole world of exquisite
music of which we know nothing.
There is another very suggestive peculiarity in the auditory apparatus
of insects. Its structure and position are something between those of
an ear and of an eye. Careful examination of the head, of one of our
domestic companions—the common cockroach or black-beetle—will reveal
two round white points, somewhat higher than the base of the long outer
antennæ, and a little nearer to the middle line of the head. These
white projecting spots are formed by the outer transparent membrane
of a bag or ball filled with fluid, which ball or bag rests inside
another cavity in the head. It resembles our own eye in having this
external transparent tough membrane, which corresponds to the cornea
or transparent membrane forming the glass of our eye-window; which,
like the cornea, is backed by the fluid in an ear-ball corresponding
to our eye-ball, and the back of this ear-ball appears to receive the
outspreadings of a nerve, just as the back of our eye is lined with
that outspread of the optic nerve forming the retina. There does not
appear to be in this or other insects a tightly stretched membrane
which, like the membrane of our ear-drum, is fitted to take up bodily
air-waves and vibrate responsively to them. But it is evidently adapted
to receive and concentrate some kind of vibration, or motion, or tremor.
What kind of motion can this be? What kind of perception does this
curious organ supply? To answer these questions we must travel beyond
the strict limits of scientific induction and enter the fairyland of
scientific imagination. We may wander here in safety, provided we
always remember where we are, and keep a true course guided by the
compass-needle of demonstrable facts.
I have said that the cornea-like membrane of the insect’s ear-bag does
not appear capable of responding to _bodily_ air-waves. This adjective
is important, because there are vibratory movements of matter that
are not bodily but molecular. An analogy may help to render this
distinction intelligible. I may take a long string of beads and shake
it into wavelike movements, the waves being formed by the movements
of the whole string. We may now conceive another kind of movement or
vibration by supposing one bead to receive a blow pushing it forward,
this push to be communicated to the next, then to the third, and so on,
producing a minute running tremor passing from end to end. This kind of
action may be rendered visible by laying a number of billiard balls or
marbles in line and bowling an outside ball against the end one of the
row. The impulse will be rapidly and invisibly transmitted all along
the line, and the outer ball will respond by starting forward.
Heat, light, and electricity are mysterious internal movements of what
we call matter (some say “ether,” which is but a name for imaginary
matter). These internal movements are as invisible as those of the
intermediate billiard balls; but if there be a line of molecules acting
thus, and the terminal one strikes an organ of sense fitted to receive
its motion, some sort of perception may follow. When such movements
of certain frequency and amplitude strike our organs of vision, the
sensation of light is produced. When others of greater amplitude and
smaller frequency strike the terminal outspread of our common sensory
nerves, the sensation of heat results. The difference between the
frequency and amplitude of the heat waves and the light waves is but
small, or, strictly speaking, there is no actual line of separation
lying between them; they run directly into each other. When a piece
of metal is gradually heated, it is first “black-hot;” this is while
the waves or molecular tremblings are of a certain amplitude and
frequency; as the frequency increases and amplitude diminishes (or, to
borrow from musical terms, as the pitch rises), the metal becomes dull
red-hot; greater rapidity, cherry red; greater still, bright red; then
yellow-hot and white-hot: the luminosity growing as the rapidity of
molecular vibration increases.
There is no such gradation between the most rapid undulations or
tremblings that produce our sensation of sound and the slowest of those
which give rise to our sensations of gentlest warmth. There is a huge
gap between them, wide enough to include another world or several other
worlds of motion, all lying between our world of sounds and our world
of heat and light, and there is no good reason whatever for supposing
that matter is incapable of such intermediate activity, or that such
activity may not give rise to intermediate sensations, provided there
are organs for taking up and sensifying (if I may coin a desirable
word) these movements.
As already stated, the limit of audible tremors is three to four
thousand per second, but the smallest number of tremors that we can
perceive as heat is between three and four millions of millions
per second. The number of waves producing red light is estimated
at four hundred and seventy-four millions of millions per second;
and for the production of violet light, six hundred and ninety-nine
millions of millions. These are the received conclusions of our best
mathematicians, which I repeat on their authority. Allowing, however, a
very large margin of possible error, the world of possible sensations
lying between those produced by a few thousands of waves and any number
of millions is of enormous width.
In such a world of intermediate activities the insect probably lives,
with a sense of vision revealing to him more than our microscopes
show to us, and with his minute eye-like ear-bag sensifying material
movements that lie between our world of sounds and our other
far-distant worlds of heat and light.
There is yet another indication of some sort of intermediate
sensation possessed by insects. Many of them are not only endowed
with the thousands of lenses of their compound eyes, but have in
addition several curious organs that have been designated “ocelli”
and “stemmata.” These are generally placed at the top of the head,
the thousand-fold eyes being at the sides. They are very much like
the auditory organs above described—so much so that in consulting
different authorities for special information on the subject I have
fallen into some confusion, from which I can only escape by supposing
that the organ which one anatomist describes as the ocelli of certain
insects is regarded as the auditory apparatus when examined in another
insect by another anatomist. All this indicates a sort of continuity of
sensation connecting the sounds of the insect world with the objects of
their vision.
But these ocular ears or auditory eyes of the insect are not his only
advantage over us. He has another sensory organ to which, with all our
boasted intellect, we can claim nothing that is comparable, unless
it be our olfactory nerve. The possibility of this I will presently
discuss.
I refer to the _antennæ_, which are the most characteristic of insect
organs, and wonderfully developed in some, as may be seen by examining
the plumes of the crested gnat. Everybody who has carefully watched
the doings of insects must have observed the curiously investigative
movements of the antennæ, which are ever on the alert, peering and
prying to right and left and upwards and downwards. Huber, who devoted
his life to the study of bees and ants, concluded that these insects
converse with each other by movements of the antennæ, and he has given
to the signs thus produced the name of “antennal language.” They
certainly do communicate information or give orders by some means;
and when the insects stop for that purpose, they face each other and
execute peculiar wavings of these organs that are highly suggestive of
the movements of the old semaphore telegraph arms.
The most generally received opinion is that these antennæ are very
delicate organs of touch, but some recent experiments made by Gustav
Hansen indicate that they are organs of smelling or of some similar
power of distinguishing objects at a distance. Flies deprived of
their antennæ ceased to display any interest in tainted meat that had
previously proved very attractive. Other insects similarly treated
appear to become indifferent to odors generally. He shows that the
development of the antennæ in different species corresponds to the
power of smelling which they seem to possess.
I am sorely tempted to add another argument to those brought forward by
Hansen, viz.: that our own olfactory nerves, and those of all our near
mammalian relations, are curiously like a pair of antennæ.
There are two elements in a nervous structure—the gray and the white;
the gray, or ganglionic portion, is supposed to be the centre or seat
of nervous power, and the white medullary or fibrous portion merely the
conductor of nervous energy.
The nerves of the other senses have their ganglia seated internally,
and bundles of tubular white threads spread outwards therefrom; but not
so with the olfactory nervous apparatus. These present two horn-like
projections that are thrust forward from the base of the brain, and
have white or medullary stems that terminate outwardly or anteriorly
in ganglionic bulbs resting upon what I may call the roof of the nose;
these bulbs throw out fibres that are composed, rather paradoxically,
of more gray matter than white. In some quadrupeds with great power of
smell, the olfactory nerves extend so far forward as to protrude beyond
the front of the hemispheres of the brain, with bulbous terminations
relatively very much larger than those of man.
They thus appear like veritable antennæ. In some of our best works
on anatomy of the brain (Solly, for example) a series of comparative
pictures of the brains of different animals is shown, extending from
man to the cod-fish. As we proceed downwards, the horn-like projection
of the olfactory nerves beyond the central hemispheres goes on
extending more and more, and the relative magnitude of the terminal
ganglia or olfactory lobes increases in similar order.
We have only to omit the nasal bones and nostrils, to continue
this forward extrusion of the olfactory nerves and their bulbs and
branches, to coat them with suitable sheaths provided with muscles for
mobility, and we have the antennæ of insects. I submit this view of the
comparative anatomy of these organs as my own speculation, to be taken
for what it is worth.
There is no doubt that the antennæ of these creatures are connected by
nerve-stalks with the anterior part of their supra-œsophageal ganglia,
_i.e._, the nervous centres corresponding to our brain.
But what kind and degree of power must such olfactory organs possess?
The dog has, relatively to the rest of his brain, a much greater
development of the olfactory nerves and ganglia than man has. His
powers of smell are so much greater than ours that we find it difficult
to conceive the possibility of what we actually see him do. As an
example, I may describe an experiment I made upon a bloodhound of the
famous Cuban breed. He belonged to a friend whose house is situated on
an eminence commanding an extensive view. I started from the garden and
wandered about a mile away, crossed several fields by sinuous courses,
climbing over stiles, and jumping ditches, always keeping the house
in view; I then returned by quite a different track. The bloodhound
was set upon the beginning of my track. I watched him from a window
galloping rapidly, and following all its windings without the least
halting or hesitation. It was as clear to his nose as a gravelled path
or a luminous streak would be to our eyes. On his return I went down
to him, and without approaching nearer than five or six yards, he
recognized me as the object of his search, proving this by circling
round me, baying deeply and savagely though harmlessly, as he always
kept at about the same distance.[8]
If the difference of development between the human and canine internal
antennæ produces all this difference of function, what a gulf may there
be between our powers of perceiving material emanations and those
possessed by insects! If my anatomical hypothesis is correct, some
insects have protruding nasal organs or out-thrust olfactory nerves as
long as all the rest of their bodies. The power of movement of these
in all directions affords the means of sensory communication over a
corresponding range, instead of being limited merely to the direction
of the nostril openings. In some insects, such as the plumed gnat, the
antennæ do not appear to be thus moveable, but this want of mobility
is more than compensated by the multitude of branchings of these
wonderful organs, whereby they are simultaneously exposed in every
direction. This structure is analogous to the fixed but multiplied eyes
of insects, which, by seeing all round at once, compensate for the want
of that mobility possessed by others that have but a single eyeball
mounted on a flexible and mobile stalk; that of the spider, for example.
Such an extension of such a sensory function is equivalent to living
in another world of which we have no knowledge and can form no
definite conception. We, by our senses of touch and vision, know the
shapes and colors of objects, and by our very rudimentary olfactory
organs form crude ideas of their chemistry or composition, through
the medium of their material emanations; but the huge exaggeration of
this power in the insect should supply him with instinctive perceptive
powers of chemical analysis, a direct acquaintance with the inner
molecular constitution of matter far clearer and deeper than we are
able to obtain by all the refinements of laboratory analyses or the
hypothetical formulating of molecular mathematicians. Add this to the
other world of sensations producible by the vibratory movements of
matter lying between those perceptible by our organs of hearing and
vision, then strain your imagination to its cracking point, and you
will still fail to picture the wonderland in which the smallest of our
fellow-creatures may be living, moving, and having their being.