Looking at the eye as a whole, Hickson r_A Text-book of Entomology Including the Anatomy, Physiology, Embryology and Metamorphoses of Insects for Use in Agricultural and Technical Schools and Colleges as Well as by the Working Entomologist

of the eye lying between the crystalline cone-layer and the true optic

nerve to be analogous with the retina of other animals. With Ciaccio,

Berger, and others, he does not regard the layer composed of the

retinulæ and rhabdoms as the equivalent of the retina of vertebrates,

etc.

=Origin of the facetted eye.=—The two kinds of eye, the simple and the

compound, are supposed to have been derived from a primitive type,

resembling the single eye (ommatidium) of the acone eye of Tipula. As

stated by Lang, “an increase of the elements of this primitive eye led

to the formation of the ocellus; an increase in number of the primitive

eyes, and their approximation, led to the formation of the compound

facet eye.” This view is suggested, he says, by the groups of closely

contiguous single eyes of the myriopods, considered in connection with

the compound eye of Scutigera. Grenacher looks upon simple (ocelli) and

compound eyes as “sisters,” not derived from one another, but from a

common parentage.

Immature insects rarely possess compound eyes; they are only known

to occur in the nymphs of Odonata and Ephemeridæ, and in the larvæ

and pupa of Corethra.

=Mode of vision by single eyes or ocelli.=—In their simplest condition,

the eyes of worms and other of the lower invertebrates, probably only

enable those animals to distinguish light from darkness. The ocelli of

spiders and of many insects, however, probably enable them, as Lubbock

remarks, to see as our eyes do. The simple lens throws on the retina an

image, which is perceived by the fine terminations of the optic nerve.

The ocelli of different arthropods differ, however, very much in degree

of complexity.

Müller considered that the power of vision of ocelli “is probably

confined to the perception of very near objects.”

“This may be inferred,” Müller states, “partly from their existing

principally in larvæ and apterous insects, and partly from several

observations which I have made relative to the position of these

simple eyes. In the genus Empusa the head is so prolonged over the

middle inferior eye that, in the locomotion of the animal, the

nearest objects can only come within the range. In _Locusta

cornuta_, also, the same eye lies beneath the prolongation of the

head.... In the Orthoptera generally, also, the simple eyes are, in

consequence of the depressed position of the head, directed

downwards towards the surface upon which the insects are

moving.”[46] Lowne considers that in the ocellus of Eristalis, the

great convexity of the lens must give it a very short focus, and the

comparatively small number of rods render the picture of even very

near objects quite imperfect and practically useless for purposes of

vision, and that the function of the ocelli is “the perception of

the intensity and the direction of light, rather than of vision, in

the ordinary acceptation of the term.”

Réaumur, Marcel de Serres, Dugès, and Forel have shown by

experiment, that in insects which possess both ocelli and compound

eyes, the former may be covered over without materially affecting

the movements of the animals, while if the facetted eyes are

covered, they act as if in the dark (Lubbock).

While Plateau regards the ocelli as of scarcely any use to the

insect, and Forel claims that wasps, humble bees, ants, etc., walk

or fly almost equally well without as with the aid of their ocelli,

Lubbock demurs to this view, and says the same experiments of

Forel’s might almost be quoted to prove the same with reference to

the compound eyes. Indeed, the writer has observed that in caves,

eyeless beetles apparently run about as freely and with as much

purpose, as their eyed relatives in the open air.

Plateau has recently shown that caterpillars which have ocelli alone

are very short-sighted, not seeing objects at a distance beyond one

or two centimetres, and it has been fully proved by Plateau and

others, that spiders, with their well-formed ocelli, are myopic, and

have little power of making out distinctly the shape of the objects

they see.

On the whole, we are rather inclined to agree with Lubbock and

Forel, that the ocelli are useful in dark places and for near

vision. They are, as Lubbock states, especially developed in

insects, such as ants, bees, and wasps, which live partly in the

open light and partly in the dark recesses of nests. Moreover, the

night-flying moths nearly all possess ocelli, while with one known

exception (Pamphila) they are wanting in butterflies.

Finally, remarks Lubbock, “Whatever the special function of ocelli

may be, it seems clear that they must see in the same manner as our

eyes do—that is to say, the image must be reversed. On the other

hand, in the case of compound eyes, it seems probable that the

vision is direct, and the difficulty of accounting for the existence

in the same animal of two such different kinds of eyes is certainly

enhanced by the fact that, as it would seem, the image given by the

medial eyes is reversed, while that of the lateral ones is direct”

(p. 181).

=Mode of vision by facetted eyes.=—The complexity of the facetted eyes

of insects is amazing, and difficult to account for unless we accept the

mosaic theory of Müller, who maintained that the distinctness of the

image formed by such an eye will be greater in proportion to the number

of separate cones. His famous theory is thus stated: “An image formed by

several thousand separate points, of which each corresponds to a

distinct field of vision in the external world, will resemble a piece of

mosaic work, and a better idea cannot be conceived of the image of

external objects which will be depicted on the retina of beings endowed

with such organs of vision, than by comparing it with perfect work of

that kind.”

[Illustration:

FIG. 267.—From Lubbock.

]

How vision is effected by a many-facetted eye is thus explained by

Lubbock: “Let a number of transparent tubes, or cones with opaque walls,

be ranged side by side in front of the retina, and separated from one

another by black pigment. In this case the only light which can reach

the optic nerve will be that which falls on any given tube in the

direction of its axis.” For instance, in Fig. 267, the light from _a_

will pass to _a′_, that from _b_ to _b′_, that from _c_ to _c′_, and so

on. The light from _c_, which falls on the other tubes, will not reach

the nerve, but will impinge on the sides and be absorbed by the pigment.

Thus, though the light from _c_ will illuminate the whole surface of the

eye, it will only affect the nerve at _c′_.

According to this view those rays of light only which pass directly

through the crystalline cones, or are reflected from their sides, can

reach the corresponding nerve-fibres. The others fall on, and are

absorbed by, the pigment which separates the different facets. Hence

each cone receives light only from a very small portion of the field of

vision, and the rays so received are collected into one spot of light.

It follows from this theory that the larger and more convex the eye, the

wider will be its field of vision, while the smaller and more numerous

are the facets, the more distinct will be the vision (Lubbock).

The theory is certainly supported by the shape and size and the immense

number of facets of the eye of the dragon-fly, which all concede to see

better, and at a longer range, than probably any other insect.

Müller’s mosaic theory was generally received, until doubted and

criticised by Gottsche (1852), Dor (1861), Plateau, and others. As

Lubbock in his excellent summary states, Gottsche’s observation

(previously made by Leeuwenhoek) that each separate cornea gives a

separate and distinct image, was made on the eye of the blow-fly,

which does not possess a true crystalline cone. Plateau’s objection

loses its force, since he seems to have had in his mind, as Lubbock

states, Gottsche’s, rather than Müller’s, theory.

Müller’s theory is supported by Boll, Grenacher, Lubbock, Watase,

and especially by Exner, who has given much attention to the subject

of the vision of insects, and is the weightiest authority on the

subject.

Gottsche’s view that each of the facetted eyes makes a distinct

image which partially overlaps and is combined with all the images

made by the other facets, was shown by Grenacher to be untenable,

after repeating Gottsche’s experiments with the eyes of moths, in

which the crystalline cones are firm and attached to the cornea. He

was thus able to remove the soft parts, and to look through the

cones and the cornea. When the microscope was focussed at the inner

end of the cone, a spot of light was visible, but no image. As the

object-glass was moved forward, the image gradually came into view,

and then disappeared again. Here, then, the image is formed in the

interior of the cone itself.

Exner attempted to make this experiment with the eye of Hydrophilus,

but in that insect the crystalline cones always came away from the

cornea. “He, however, calculated the focal length, refraction, etc.,

of the cornea, and concluded that, even if, in spite of the

crystalline cone, an image could be formed, it would fall much

behind the retinula.”

“In these cases, then,” adds Lubbock, “an image is out of the

question. Moreover, as the cone tapers to a point, there would, in

fact, be no room for an image, which must be received on an

appropriate surface. In many insect eyes, indeed, as in those of the

cockchafer, the crystalline cone is drawn out into a thread, which

expands again before reaching the retinula. Such an arrangement

seems fatal to any idea of an image.”

Lubbock thus sums up the reasons which seem to favor Müller’s theory

of mosaic vision, and to oppose Gottsche’s view: “(1) In certain

cases, as in Hyperia, there are no lenses, and consequently there

can be no image; (2) the image would generally be destroyed by the

crystalline cone; (3) in some cases it would seem that the image

would be formed completely behind the eye, while in others, again,

it would be too near the cornea; (4) a pointed retina seems

incompatible with a clear image; (5) any true projection of an image

would in certain species be precluded by the presence of

impenetrable pigment, which only leaves a minute central passage for

the light-rays; (6) even the clearest image would be useless, from

the absence of a suitable receptive surface, since both the small

number and mode of combination of the elements composing that

surface seem to preclude it from receiving more than a single

impression; (7) no system of accommodation has yet been discovered;

finally (8), a combination of many thousand relatively complete eyes

seems quite useless and incomprehensible.”

In his most recent work (1890) on the eyes of crustacea and insects,

Exner states that the numerous simple eyes which make up the

compound eye have each a cornea, but it is more or less flat, and

the crystalline part of the eye has not the shape of a lens, but of

a “lens cylinder,” that is, of a cylinder which is composed of

sheets of transparent tissue, the refracting powers of which

decrease toward the periphery of the cylinder. If an eye of this

kind is removed and freed of the pigment which surrounds it, objects

may be looked at through it from behind; but its field of vision is

very small, and the direct images received from each separate eye

are either produced close to one another on the retina (or rather

the retinulæ of all the eyes) or superposed. In this last case no

less than thirty separate images may be superposed, which is

supposed to be of great use to night-flying insects. Exner claims

that many other advantages result from the compound nature of an

insect’s eye. Thus the mobile pigment, which corresponds to our

iris, can take different positions, either between the separate eyes

or behind the lens cylinders, in which case it acts as so many

screens to intercept the over-abundance of light. Exner finds that

with its compound eyes the common glow-worm (Lampyris) is capable of

distinguishing large signboard letters at a distance of ten or more

feet, as well as extremely fine lines engraved one-hundredth of an

inch apart, if they are at a distance of less than half an inch from

the eye. Exner substantiates the truth of the results of Plateau’s

experiments, and claims that while the compound eye is inferior to

the vertebrate eye for making out the forms of objects, it is

superior to the latter in distinguishing the smallest movements of

objects in the total field of vision.

More recently Mallock has given some optical reasons to show that

Müller’s view is the true one. He concludes, and thus agrees with

Plateau, that insects do not see well, at any rate as regards their

power of defining distant objects, and their behavior certainly

favors this view. It might be asked, What advantage, then, have

insects with compound eyes over those with simple eyes? Mallock

answers, that the advantage over simple-eyed animals lies in the

fact that there is hardly any practical limit to the nearness of the

objects they can examine. “With the composite eye, indeed, the

closer the object the better the sight, for the greater will be the

number of lenses employed to produce the impression; whereas, in the

simple eye the focal length of the lens limits the distance at which

a distinct view can be obtained.” He gives a table containing

measures of the diameters and angles between the axes of the lenses

of various insect eyes, and states that the best of the eyes would

give a picture about as good as if executed in rather coarse

woodwork and viewed at a distance of a foot, “and although a distant

landscape could only be indifferently represented on such a

coarse-grained structure, it would do very well for things near

enough to occupy a considerable part of the field of view.”

=The principal use of the facetted eye to perceive the movements of

animals.=—Plateau adopts Exner’s views as to the use of the facetted eye

in perceiving the movements of other animals. He therefore concludes

that insects and other arthropods with compound eyes do not distinguish

the form of objects; but with Exner he believes that their vision

consists mainly in the perception of moving bodies.

Most animals seem but little impressed by the form of their enemies

or of their victims, though their attention is immediately excited

by the slightest displacement. Hunters, fishermen, and entomologists

have made in confirmation of this view numerous and demonstrative

observations.

Though the production of an image in the facetted eye of the insect

seems impossible, we can easily conceive, says Plateau, how it can

ascertain the existence of a movement. Indeed, if a luminous object

is placed before a compound eye, it will illuminate a whole group of

simple eyes or facets; moreover, the centre of this group will be

clearer than the rest. Every movement of the luminous body will

displace the centre of clearness; some of the facets not illuminated

will first receive the light, and others will reënter into the

shade; some nervous terminations will be excited anew, while those

which were so formerly will cease to be. Hence the facetted eyes are

not complete visual organs, but mainly organs of orientation.

Plateau experimented in the following way: In a darkened room, with

two differently shaped but nearly equal light-openings, one square

and open, the other subdivided into a number of small holes, and

therefore of more difficult egress, he observed the choices of

opening made by insects flying from the other end of the room.

Careful practical provisions were made to eliminate error; the

light-intensity of the two openings was as far as possible equalized

or else noted, and no trees or other external objects were in view.

The room was not darkened beyond the limit at which ordinary type

ceases to be readable, otherwise the insects refused to fly (it is

well known that during the passage of a thick cloud insects usually

cease to fly). These observations were made on insects both with or

without ocelli, in addition to the compound eyes, and with the same

results.

From repeated experiments on flies, bees, etc., butterflies and

moths, dragon-flies and beetles, Plateau concludes that insects with

compound eyes do not notice differences in form of openings in a

half-darkened room, but fly with equal readiness to the apparently

easy and apparently difficult way of escape; that they are attracted

to the more intensely lighted opening, or to one with apparently

greater surface; hence he concludes that they cannot distinguish the

form of objects, at least only to a very slight extent, though they

readily perceive objects in motion.

One result of his experiments is that insects only utilize their

eyes to choose between a _white_ luminous orifice in a dark chamber,

or another orifice, or group of orifices, _equally white_. They are

guided neither by odorous emanations nor by differences of color. He

thinks that bees have as bad sight and act almost exactly as flies.

From numerous experiments on Odonata, Coleoptera, Lepidoptera,

Diptera, and Hymenoptera Plateau arrives provisionally at the

following conclusions:

1. Diurnal insects have need of a quick strong light, and cannot

direct their movements in partial obscurity.

2. Insects with compound eyes do not notice differences of form

existing between two light orifices, and are deceived by an excess

of luminous intensity as well as by the apparent excess of surface.

In short, they do not distinguish the form of objects, or if they

do, distinguish them very badly.

Lubbock, however, does not fully accept Plateau’s experiments with

the windows, and thinks they discern the form of bodies better than

Plateau supposes.

=How far can insects see?=—It is now supposed that no insects can

perceive objects at a greater distance than about six feet. On an

average Lepidoptera can see the movements of rather large bodies

1.50 meters, but Hymenoptera only 58 cm., and Diptera 68 cm.; while

the firefly (Lampyris) can see tolerably well the form of large

objects at a distance of over two meters.

Until further experiments are made, it seems probable, then, that

few if any insects have acute sight, that they see objects best when

moving, and on the whole—except dragon-flies and other predaceous,

swiftly flying insects, such as certain flies, wasps, and bees,

which have very large rounded eyes—insects are guided mainly rather

by the sense of smell than of sight.

=Relation of sight to the color of eyes.=—It appears from the

observations of Girschner that those Diptera with eyes of a uniform

color see better than those with brightly banded or spotted eyes.

Thus those flies (Asilidæ, Empidæ, Leptidæ, Dolichopidæ) whose

predaceous habits requires good or quick sight have uniformly dark

eyes, as have also such flies as live constantly on the wing,

_i.e._, the holoptic Bombyliidæ, Syrphidæ, Pipunculidæ, etc., whose

eyes are also very large.

Those flies whose larvæ are parasitic on other animals have eyes of

a uniform color that they may readily detect the most suitable host

for their young; such are the Bombyliidæ, Conopidæ, Pipunculidæ, and

Tachinidæ.

Certain flies which live in the clear sunlight, as many Dolichopidæ,

some Bombyliidæ, and certain Tabanidæ (Tabanus, Chrysops,

Hæmatopota), and which are often easily caught with the hand, have

eyes spotted or banded with bright or metallic colors. This is also

a sexual trait, as the males of some horse-flies visiting flowers

have eyes of a single color, the spots and bands surviving only on

the lower and hinder parts of the eye, while their voracious

blood-sucking females have the entire eye spotted or banded (Kolbe).

=The color-sense of insects.=—Insects, as Spengel first suggested,

appear to be able to distinguish the color of objects. Lubbock has

experimentally proved that bees, wasps, and ants have this power,

blue being the favorite color of the honey-bee, and violet of ants,

which are sensitive to ultra-violet rays.

It is well known that butterflies will descend from a position high

in the air, mistaking white bits of paper for white flowers; while,

as we have observed, white butterflies (Pieris) prefer white

flowers, and yellow butterflies (Colias) appear to alight on yellow

flowers in preference to white ones.

The late Mr. S. L. Elliott once informed us that on a red barn with

white trimmings he observed that white moths (Spilosoma, Hyphantria,

and _Acronycta oblinita_) rested on the white parts, while on the

darker, reddish portions sat Catocalæ and other dark or reddish

moths. Gross observed that house-flies would frequent a bluish green

ring on the ceiling of his chamber; but if it were covered by white

paper, the flies would leave the spot, though they would return as

soon as the paper ring was removed (Kolbe). We have observed that

house-flies prefer green paper to the yellowish wall of a kitchen,

but were not attracted to sheets of a Prussian blue paper, attached

to the same wall and ceiling.

It is generally supposed that the shape and high colors of flowers

attract insects; but Plateau has made a number of ingenious

experiments which tend to disprove this view. He used in his

investigations the dahlia, with its central head of flowerets, which

contrast so strongly with the corolla. He finds (1) that insects

frequent flowers which have not undergone any mutilation, but whose

form and colors are hidden by green leaves. (2) Neither the shape

nor lively colors of the central head (capitulum) seem to attract

them. (3) The gayly colored peripheral flowerets of simple dahlias

and, consequently, of the heads of other composite flowers, do not

play the rôle of signals, such as has been attributed to them. (4)

The insects are evidently guided by another sense than that of

sight, and this sense is probably that of smell.

LITERATURE ON THE EYES AND VISION

_a_. General

=Serres, Marcel de.= Mémoires sur les yeux composés et les yeux lisses

des insectes. Montpellier, 1813.

=Müller, Johannes.= Zur vergleichenden Physiologie des Gesichtssinnes

der Menschen und der Tiere. 8 Taf. Leipzig, 1826.

—— Ueber die Augen des Maikäfers. (Meckel’s Archiv f. Anat. u. Phys.,

1829, pp. 177–181; Ann. d. Sc. nat., 1829, sér. 1, xviii, pp.

108–112.)

=Dujardin, F.= Sur les yeux simples ou stemmates des animaux

articulés. (C. R. Acad. Sci., Paris, 1847, xxv, pp. 711–714.)

=Gottsche, C. M.= Beitrag zur Anatomie und Physiologie des Auges der

Krebse und Fliegen. (Müller’s Archiv für Anat. u. Phys., 1852, pp.

483–492. Figs.)

=Murray, Andrew.= On insect vision and blind insects. (Edinburgh New

Phil. Jour., new ser. vi, 1857, pp. 120–138.)

=Claparède, Édouard.= Zur Morphologie der zusammengesetzten Augen bei

den Arthropoden. (Zeitschr. f. wissensch. Zool., 1859, x, pp.

191–214, 3 Taf.)

=Dor, H.= De la vision chez les Arthropodes. (Archives Sci. Phys, et

Nat., 1861, xii, p. 22, 1 Pl.)

=Landois, H.= Die Raupenaugen (Ocelli compositi mihi). (Zeitschr. f.

wissensch. Zool., xvi, 1866, pp. 27–44, 1 Taf.)

—— und =W. Thelen.= Zur Entwicklungsgeschichte der fasettierten Augen

von _Tenebrio molitor L._ (Zeitschr. f. wissensch. Zool., xvii,

1867, pp. 34–43, 1 Taf.)

=Schultze, Max.= Untersuchungen über die zusammengesetzten Augen der

Krebsen und Insecten. Bonn, 1868.

=Schmidt, Oscar.= Die Form der Krystallkegel in Arthropodenauge.

(Zeitschr. f. wissensch. Zool., xxx, Suppl., 1878, pp. 1–12, 1 Taf.)

=Grenacher, H.= Untersuchungen ueber das Sehorgan der Arthropoden,

insbesondere Spinnen, Insecten und Crustaceen. (Göttingen, 1879, 4º,

pp. 1–188, 11 Taf.)

=Reichenbach, H.= Wie die Insekten sehen. Fig. (Daheim, xvi Jahrg.,

1880, pp. 284–286.)

=Poletajew, N.= Ueber die Ozellen und ihr Sehvermögen bei den

Phryganiden. (Horæ Soc. Ent. Ross., 1884, xviii, p. 23, 1 Taf. In

Russian.)

=Hickson, S. J.= The eye and optic tract of insects. (Quart. Journ.

Micr. Sc., ser. 2, xxv, 1885, pp. 215–221, 3 Pls.)

=Notthaft, Jul.= Ueber die Gesichtswahrnehmungen vermittelst des

Fazettenauges. (Abhandl. Senckenberg. naturf. Ges., xii., 1880, pp.

35–124, 5 Taf.)

—— Die physiologische Bedeutung des fazettierten Insektenauges.

(Kosmos, 1886, xviii, pp. 442–450, Fig.)

=Mark, E. L.= Simple eyes in arthropods. (Bull. Mus. Comp. Zool.,

1887, xiii, pp. 49–105, 5 Pls.)

=Girschner, E.= Einiges über die Färbung der Dipterenaugen. (Berlin.

Ent. Zeitschr., 1888, xxxi, pp. 155–162, 1 Taf.)

=Graber, V.= Das unicorneale Tracheatenauge. (Archiv f. Mikroskop.

Anat., xvii, 1879, pp. 58–93, 3 Taf.; Nachtrag, p. 94.)

—— Fundamentalversuche über die Helligkeits- und Farbenempfindlichkeit

augenloser und geblendeter Tiere. (Sitzgs.-Ber. Akad. Wissensch.,

Wien, 1883, lxxxvii, pp. 201–236.)

=Dahl, Fr.= Die Insekten können Formen unterscheiden. (Zool. Anz.,

xii, 1889, pp. 243–247.)

=Ciaccio, G. V.= Figure dichiarative della minuta fabbrica degli occhi

de’ Ditteri. Bologna, 1884, 12 Taf., 30 pp.

—— Della minuta fabbrica degli occhi de’ Ditteri. (Mem. Accad.

Bologna, 1886, ser. 4, vi, pp. 605–660.)

—— Sur la forme et la structure des facettes de la cornée et sur les

milieux refringents des yeux composés des Muscidés. (Journ. Micr.,

Paris, 1889, xiii Année, pp. 80–84.)

=Carrière, J.= On the eyes of some invertebrata. (Quart. Journ. Micr.

Sc. 1884, ser. 2, xxiv, pp. 673–681, 1 Pl.)

—— Ueber die Arbeiten von Viallanes, Ciaccio und Hickson. (Biolog.

Centralblatt, v, 1885, pp. 589–597.)

—— Die Sehorgane der Tiere vergleichend anatomisch dargestellt.

München u. Leipzig, 1885, 205 pp., 147 Figs., 1 Taf.

—— Kurze Mitteilungen aus fortgesetzten Untersuchungen über die

Sehorgane. (Zool. Anz., ix Jarhg., 1886, pp. 141–147, 479–481,

496–500.)

=Forel, A.= Les fourmis de la Suisse. (Neue Denkschriften der schweiz.

naturforsch. Gesellsch. xxvi. 1874, pp. 480, 2 Pls.) Separate. pp.

iv u. 457. Genève.

—— Beitrag zur Kenntnis der Sinnesempfindungen der Insekten. (Mitteil.

d. Münchener Ent. Vereins, ii Jahrg., 1878, pp. 1–21.)

—— Sensations des insectes. (Recueil Zool. Suisse, iv, 1886 et 1887.)

=Plateau, F.= L’instinct chez les insectes mis en défaut par les

fleurs artificielles? (Assoc. française avancement des sciences.

Congrès de Clermont. Ferrand, 1876.)

=Plateau, F.= Recherches expérimentales sur la vision chez les

insectes. Les insectes distinguent-ils la forme des objets? (Bull.

Acad. Belg. 3 Sér. x, 1885, pp. 231–250.)

—— Recherches expérimentales sur la vision chez les insectes.

1. Part, _a_. Résumé des travaux effectués jusqu’en 1887 sur la

structure et le fonctionnement des yeux simples. _b_. Vision chez

les Myriapodes. (Ibid. Sér. 3, xiv, 1887, pp. 407–448, 1 Pl.)

3. Part, _a_. Vision chez les chenilles, _b_. Rôle des ocelles

frontaux chez les insectes parfaits. (Ibid. Sér. 3, xv, 1888, pp.

28–91.)

4. Part. Vision à l’aide des yeux composés. _a_. Résumé

anatomo-physiologique. _b_. Expériences comparatives sur les

insectes et sur les vertébrés. (Mém. cour. et autres Mém. Acad.

Belg. 1888, xliii, pp. 1–91, 2 Pls.)

5. Part, _a_. Perception des mouvements chez les insectes. _b_.

Addition aux recherches sur le vol des insectes avenglés. _c_.

Résumé général. (Bull. Acad. Belg. 1888, sér. 3, xvi, pp. 395–457, 1

Pl.)

—— Recherches expérimentales sur la vision chez les Arthropodes, 2 Pls.

(Mém. couronn. et autres Mém. publ. p. l’Acad. Roy. d. Sciences, etc.,

de Belgique, xliii, Bruxelles, 1889.)

=Watase, S.= On the morphology of the compound eyes in the Arthropoda.

(Studies from biol. laborat. Johns-Hopkins Univ., 1890, pp. 287–334, 4

Pls.)

=Stefanowska, M.= La disposition histologique du pigment dans les yeux

des Arthropodes. (Recueil Zool. Suisse, 1890, pp. 151–200, 2 Pls.)

=Pankrath, O.= Das Auge der Raupen und Phryganiden larven. (Zeitschr. f.

wissensch. Zool., 1890, xlix, pp. 690–708, 2 Taf.)

=Lowne, B. Th.= On the modifications of the simple and compound eyes of

insects. (Philos. Trans. Roy. Soc., London, clxix, 1878, pp. 577–602, 3

Pls.)

—— On the structure and functions of the eyes of Arthropoda. (Proc. Roy.

Soc., London, 1883, xxxv, pp. 140–145.)

—— On the compound vision and the morphology of the eye in insects.

(Trans. Linn. Soc., London, 1884, ii, pp. 389–420, 4 Pls.)

—— On the structure of the retina of the blow-fly (_Calliphora

erythrocephala_). (Jour. Linn. Soc., London, 1890, xx, pp. 406–417, 1

Pl.)

=Patten, W.= Eyes of molluscs and arthropods. (Journal of Morphol.,

Boston, 1887, i, pp. 67–92, 1 Pl.; Mitteil. Zool. Stat. Neapel, vi,

1886, pp. 542–756, 5 Taf.)

—— Studies on the eyes of arthropods.—1. Development of the eyes of

Vespa, with observations on the ocelli of some insects. (Ibid., pp.

193–226, 1 Pl.)—2. Eyes of Acilius. (Ibid., 1888, ii., pp. 190–97, 7

Pls.)

—— On the eyes of molluscs and arthropods. (Zool. Anzeiger, 1887, x

Jahrg., pp. 256–261.)

—— Is the ommatidium a hair-bearing sense-bud? (Anatom. Anzeiger, 1890,

v, pp. 353–359, 4 Figs.)

=Exner, S.= Ueber das Sehen von Bewegungen und die Theorie des

zusammengesetzten Auges. (Sitzgsber. d. math. naturwiss. Cl. kais. Akad.

d. Wissens. Wien, lxxii Jahrg., 1875, 3 Abt. Physiologie, pp. 156–190, 1

Taf.)

—— Die Frage von der Funktionsweise der Fazettenauges. (Biolog.

Centralblatt, i, 1881, pp. 272–281.)

—— Das Netzhautbild des Insektenauges. (Sitzgsber. kais. Akad. d.

Wissensch. Wien, 1889, xcviii, 3 Abt., pp. 13–65, 2 Taf. u. 7 Figs.)

—— Durch Licht bedingte Verschiebungen des Pigmentes im Insektenauge und

deren physiologische Bedeutung. (Ibid., pp. 143–151, 1 Taf.)

=Exner, S.= Die Physiologie der fazettierten Augen von Krebsen und

Insekten, 7 Taf., 1, Lichtdruck u. 23 Holzschn. pp. 206. Wien, F.

Deuticke, 1891.

=Lubbock, John.= On the senses, instincts, and intelligence of animals,

with special reference to insects. London, 1888, pp. 292.

=Mallock, A.= Insect sight and the defining power of composite eyes.

(Proc. Roy. Soc., London, 1894, lv, pp. 85–90, 3 Figs.)

_b_. The color-sense

=Nussli, J.= Ueber den Farbensinn der Bienen. (Schweiz. Bienenzeitung,

N. F., ii Jahrg., 1879, pp. 238–240.)

=Kramer.= Der Farbensinn der Bienen. (Ibid., iii Jahrg., 1880, pp.

179–198.)

=Gross, Wilhelm.= Ueber den Farbensinn der Tiere, insbesondere der

Insekten. (Isis v. Russ., v Jahrg., 1880, pp. 292–294, 300–302,

308–309.)

=Lubbock, John.= Ants, bees, and wasps. London, 1882, pp. 448. Also On

the senses, etc., of animals, 1889.

=Graber, Vitus.= Grundlinien zur Erforschung des Helligkeits und

Farbensinnes der Tiere. Prag u. Leipzig, 1884, pp. 322. (See also p.

262.)

=Forel, Auguste.= Les Fourmis perçoisent-elles l’ultra-violet avec

leurs yeux ou avec leur peau? (Arch. Sci. Phys. Nat. Genève, 1886, 3

sér., xvi, pp. 346–350.)

Also the works of Darwin, Wallace, F. Müller, Grant Allen’s The Color

Sense (1879), Beddard’s Animal Coloration, etc.

_b_. The organs of smell

The seat of the organs of smell is mainly in the antennæ, and they may

be regarded as the principal olfactory organs. For our present knowledge

of the anatomy and physiology of the olfactory organs of insects we are

mainly indebted to the recent investigations of Hauser and of Kraepelin.

The following historical and critical remarks are translated from

Kraepelin’s able treatise:

=Historical sketch of our knowledge of the organs of smell.=—In the

first half of the last century began the inquiries as to the seat of

the sense of smell in the arthropods. Thus Réaumur, in his Mémoires

(i, p. 283; ii, 224), expressed the view that in the antennæ was

situated a special organ which might be an organ of smell.

Lesser, Roesel, Lyonet, Bonnet, and others expressed the same

opinion. Before this Sulzer suggested that an “unknown sense” might

exist in the antennæ; others regarded the stigmata as organs of

smell, as these were considered the natural passages for the

olfactory currents. Duméril, in two special treatises as well as in

his Considérations générales, sought to prove the theory as to the

seat of the organs of smell in the stigmata.

Against both of these leading views as to the seat of the sense of

smell were expressed, in the last century, different opinions. Thus

Comparetti thought that the sense of smell might be localized in

very different points of the head, in the antennal club of

lamellicorns, in the sucking-tube of Lepidoptera, in special frontal

holes of flies and Orthoptera, etc., while Bonsdorf considered the

palpi as organs of smell.

Thus four different views, confused, were held at the opening of

this century; the Hamburg zoölogist, M. C. S. Lehrman, in three

different treatises, brought together all the hitherto known

observations and arguments, treated them critically, and completed

them by his own extended studies. Lehrman adopted the opinions of

Reimarus, Baster, Duméril, and Schelver, that the stigmata presented

the most convenient place for the site of the organs of smell.

Cuvier followed throughout the lead of Lehrman, but Latreille

returned to the view of the perception of smell by the antennæ,

while Treviranus considered the mouth of arthropods as the probable

site of the sense of smell, an opinion which, before his time,

Huber, in his experiments on bees, had thought to be correct. Marcel

de Serres (1811) returned again to the palpi, and asserted—at least

in the Orthoptera—their functions to be olfactory, while Blainville,

ten years later, again expressed anew the old opinion that the

antennæ, or at least their terminations, were organs of smell. Up to

that date there was an uncertainty as to the seat of the organs both

of smell and hearing. Fabricius, indeed, had already, in 1783,

thought he had found an organ of hearing at the base of the outer

antenna. In 1826 J. Müller mentioned an already well-known organ in

the abdomen of crickets as an organ of hearing. Müller, however, was

doubtful, from the fact that the nerve passing to this organ arose,

not from the brain, but from the third thoracic ganglion; but,

notwithstanding, he remarks: “Perhaps we have not found the organ of

hearing in insects because we sought for it in the head.” This

discovery was afterwards considerably broadened and extended by

Siebold’s work, for the views of these naturalists on the seat of

both organs had a definite influence, especially in Germany. For

awhile, indeed, Müller’s hypothesis stood in complete contradiction,

so that during the following decennial was presented anew the

picture of opposing observations and opinions as to the nature of

the organs of smell. While Robineau-Desvoidy, at the end of the

twentieth year, and also later, in different writings, strove

energetically for the olfactory nature of the antennæ,

Straus-Dürckheim held fast to the view that the tracheæ possessed

the function under discussion. At the same period Kirby and Spence,

in their valuable Introduction to Entomology, maintained that “two

white cushions on the under side of the upper lip” in the mouth of

biting insects formed a nose or “rhinarium” peculiar to insects.

This opinion was afterwards adopted by Lacordaire (Introduction à

Entomologie), and also by Oken in his Lehrbuch der Naturphilosophie,

while Burmeister, rejecting all the views previously held, believed

that insects might perhaps smell “with the inner upper surface of

the skin.” Müller’s locust’s ear he regarded as a vocal organ.

Besides these occasional expressions of opinion, the French

literature of the thirtieth and fortieth years of this century

recorded a long series of special works, with weighty experimental

and physiological contents, on this subject. Thus Lefebre, in 1838,

described the experiments which he made on bees, and which seemed to

assign the seat of the sense of smell to the antennæ. Dugès reported

similar researches on the Scolopendræ, and Pierret thought that the

great development of the antennæ in the male Bombycidæ might be

similarly interpreted. Driesch sought to give currency to the views

of Bonsdorf, Lamarck, and Marcel de Serres, that the sense of smell

was localized in the palpi, though Duponchel went back to the old

assertion of æroscepsis of Lehrman, _i.e._ of the air-test through

the antennæ, and Goureau again referred the seat of the sense of

smell to the mouth. In England, Newport at this period put forth a

work in which he considered the antennæ as organs of touch and

hearing, and the palpi as organs of smell—a view which, as regards

the antennæ, was opposed by Newman.

Thus the contention as to the use of the antennæ and the seat of the

organs of smell and hearing fluctuated from one side to the other,

and when in 1844 Küster, by reason of his experiments on numerous

insects, again claimed that “the antennæ are the smelling organs of

insects,” he argued on a scientific basis; yet v. Siebold and

Stannius (1848), in their valuable Lehrbuch der vergleichenden

Anatomie (p. 581), remarked that “organs of smell have not yet with

certainty been discovered in these animals.”

The following decennial was of marked importance in the judgment of

many disputed questions. Almost contemporaneously with Siebold and

Stannius’ Lehrbuch appeared an opportune treatise by Erichson, in

which this naturalist first brought forward certain anatomical data

as to the structure of the antennæ of insects. In a great number of

insects Erichson described on the upper surface of the antennæ

peculiar minute pits, “pori,” which, according to him, were covered

by a thin membrane, and to which he ascribed the perception of

smell. A still more thorough work on this subject was published in

the following year by Burmeister, who recognized in the pits of

lamellicorns many small tubercles and hairs; and about the same time

Slater, as also Pierret and Erichson before him had done, out of the

differences of the antennal development in the males and females in

flesh and plant-eating insects, brought together the proof of the

olfactory function of the antennæ. But the most valuable work of

this period is that of Perris, who, after a review of previous

opinions, by exact observations and experiments, a model of their

kind, sought to discover the seat of the sense of smell. He comes to

the conclusion that the antennæ, and perhaps also the palpi, may

claim this sense, and finds full confirmation of Dufour’s views, and

adopts as new the physiological possibility expressed by Hill and

Bonnet, that the antennæ might be the seat of both senses—those of

smell and hearing.

The beautiful works of Erichson, Burmeister, and Perris could not

remain long unnoticed. In 1857 Hicks published complete researches

on the peculiar nerve-endings which he had found in the antennæ,

also in the halteres of flies and the wings of all the other groups

of insects, and which he judged to be for the perception of smell.

But Erichson’s and Burmeister’s “pori” were by Lespès, in 1858,

explained to be so many auditory vesicles with otoliths. This view

was refuted by Claparède and Claus without their deciding on any

definite sense. Leydig first made a decided step in advance. In

different writings this naturalist had busied himself with the

integumental structures of arthropods, and declared Erichson’s view

as to the olfactory nature of the antennal pits as the truest,

before he, in his careful work on the olfactory and auditory organs

of crabs and insects, had given excellent representations of the

numerous anatomical details which he had selected from his extensive

researches in all groups of arthropods. Besides the pits which were

found to exist in Crustacea, Scolopendræ, beetles, Hymenoptera,

Diptera, Orthoptera, Neuroptera, and Hemiptera, and which had only

thus far been regarded as sense-organs, Leydig first calls attention

to the widely distributed pegs and teeth, also considering them as

sense-organs. “Olfactory teeth,” occurring as pale rods, perforated

at the end, on the surface of the antennæ of Crustacea, Myriopoda,

Hymenoptera, Lepidoptera, Coleoptera, are easily distinguished, and

besides the “olfactory pegs” of the palpi, may be claimed as organs

of smell. The nerve-end apparatus first discovered by Hicks in the

halteres and wings, Leydig thinks should be ranked as organs of

hearing.

There was still some opposition to Leydig’s opinion that in the

insects the sense of smell is localized in the antennæ (teeth and

pits), and here the work of Hensen might be mentioned, which in 1860

had a decided influence upon the conclusion of some inquiries.

Thus Landois denied that the antennæ had the sense of smell, and

declared that the pits in the antennæ of the stag beetle were

auditory organs. So, also, Paasch rejected Leydig’s conclusion,

while he sought to again reinstate the old opinion of Rosenthal as

to the olfactory nature of the frontal cavity of the Diptera. In

spite of the exact observations and interesting anatomical

discoveries of Forel in ants, made in 1874, there appeared the great

work of Wolff on the olfactory organs of bees, in which this

observer, with much skill and acuteness, sought to give a basis for

the hypothesis of Kirby and Spence that the seat of the sense of

smell lay in the soft palatine skin of the labrum within the mouth

(_i.e._ the epipharynx). Joseph, two years later, drew attention to

the stigmata as olfactory organs, referring to the olfactory girdle,

and Forel sought by an occasional criticism of Wolff’s conclusions

to prove experimentally the olfactory function of the antenna; but

Graber, in his widely read book on insects, defended the Wolffian

“nose” in the most determined way, and denied to the antennæ their

so often indicated faculty of smell. In 1879 Berté thought he had

observed in the antenna of the flea a distinct auditory organ, and

Lubbock considered the organs of Forel in the antennæ of ants as a

“microscopic stethoscope.” In 1879 Graber described a new

otocyst-like sense-organ in the antennæ of flies, which was

accompanied by a complete list of all the conceivable forms of

auditory organs in arthropods. In this work Graber described in

Musca and other Diptera closed otocysts with otoliths and auditory

hairs, as Lespès had previously done. But Paul Mayer, in two essays,

refuted this view in a criticism of the opinion of Berté, referring

the “otocysts with otoliths” to the well-known antennal pits into

which tracheæ might pass. Mayer did not decide on the function of

the hairs which extend to the bottom of the pits; while in the most

recent research, that of Hauser, the author again energetically

contended for the olfactory function of the antennæ. Both through

physiological experiments and detailed anatomical investigations

Hauser sought to prove his hypothesis, as Pierrot, Erichson, Slater,

and others had done before him, besides working from an evolutional

point of view. In a purely anatomical aspect, especially prominent

are his discovery of the singularly formed nerve-rods in the pits

and peg-like teeth of the Hymenoptera and their development, as well

as the assertion that numerous hairs in the pits described by

Leydig, Meyer, etc., should be considered as direct terminations of

nervous fibres passing into the pits. In the pits he farther, with

Erichson, notices a serous fluid, which may serve as a medium for

the perception of smells. Among the latest articles on this subject

are those of Künckel and Gazagnaire, which are entirely anatomical,

while the latest treatise of Graber on the organs of hearing in

insects opposes Hicks’s theory of the olfactory function of the

nerve-end apparatus in the halteres, wings, etc., and argues for the

auditory nature of these structures. Finally, according to Voges,

the sense of smell is not localized, but spread over the whole body.

My own observations on different groups of insects agree, in

general, with those of Perris, Forel, and Hauser, without being in a

position to confirm or deny the varying relations of the Hemiptera.

That irritating odorous substances (chloroform, acetic acid) cause

the limbs to move in sympathy with the stimulus, I have seen several

times in Acanthosoma; still it may be a gustatory rather than

olfactory stimulus.

Turning now from speculation and simple observation to exact

anatomical and histological data, the nerve-end apparatus seems to

have a distinct reference to the perception of odors. It comprises a

structure composed of nervous substances which are enclosed in a

chitinous tube, and either only stand in relation to the surrounding

bodies by the perforated point, or pass to the surface as free

nerve-fibrillæ.

In insects there is a remarkable and fundamental difference in the

structures of the parts supposed to be the organs of smell. Erichson

was acquainted only with the “pori” covered by a thin membrane; but

Burmeister, in his careful work on the antennæ of the lamellicorns,

distinguished pits at the bottom of which hairs rise from a cup-like

tubercle, from those which were free from hairs. Leydig afterwards

was the first to regard as olfactory organs the so-called pegs

(_kegel_), a short, thick, hair-like structure distinctly perforated

at the tip, which had already, by Lespès in Cercopis, etc., been

described as a kind of tactile papilla. Other very peculiar

olfactory organs of different form, Forel (Fourmis de la Suisse)

discovered in the antennæ of ants, which Lubbock incorrectly

associated with the nerve-end apparatus found by Hicks in other

insects.

As the final result of his researches Kraepelin states that the great

variety of antennal structures previously described may be referred to a

single common fundamental type of a more or less developed free or

sunken hair-like body which stands in connection by means of a wide

pore-canal with a many-nucleated ganglion-cell. The latter sends only a

relatively slender nerve-fibre (axial cord) through the pore-canal into

the hair; but the same is enclosed by epithelial cells which surround

the pore-canal.

Hauser’s researches on the organs of smell in insects were so carefully

made and conclusive that our readers will, we feel sure, be glad to have

laid before them in detail the facts which prove so satisfactorily that

the antennæ of most insects are olfactory rather than auditory in their

functions.

=Physiological experiments.=—First of all one should observe as exactly

as possible the normal animal in its relation to certain odorous

substances, whose fumes possess no corrosive power or peculiarities

interfering with respiration; then remove the antennæ and try after

several days to ascertain what changes have taken place in the relation

of the animal to the substance. In order to come to no false results it

is often necessary to let the insects operated upon rest one or two

days, for immediately after the operation they are generally so restless

that a careful experiment is impossible.

The extirpation of the antennæ is borne by different insects in

different ways; many bear it very easily, and can live for months after

the operation, while others die in the course of a few days after the

loss of these appendages. The animals seem to be least injured if the

operation is performed at a time when they are hibernating. _Pyrrhocoris

apterus_, and many other insects, afforded a very striking proof of this

relation.

Experiments made by placing the antennæ in liquid paraffine so as to

cover them with a layer of paraffine, thus excluding the air, gave the

same result as if the antennæ had been removed.

The experiments may be divided, according to their object, into three

groups. Experiments of the first kind were made on insects in their

relation to strong-smelling substances, as turpentine, carbolic acid,

etc., before and after extirpation of the antennæ. The second group

embraces experiments on the relation of animals as regards their search

for food; and finally the third group embraces experiments on the

relation of the sexes relative to reproduction before and after the

extirpation of the antennæ.

=Relation of insects to smelling substances before and after the loss of

their antennæ.=—Taking a glass rod dipped in carbolic acid and holding

it within 10 cm. of _Philonthus œneus_, found under stones at the end of

February, it was seen to raise its head, turn it in different

directions, and to make lively movements with its antennæ. But scarcely

had Hauser placed the rod close to it when it started back as if

frightened, made a sudden turn, and rushed, extremely disturbed, in the

opposite direction. When he removed the glass rod, the creature busied

itself for some time with its antennæ, while it drew them, with the aid

of its fore limbs, through its mouth, although they had not come into

direct contact with the carbolic acid. There was the same reaction

against oil of turpentine, and it was still more violent against acetic

acid.

After having many times carefully tested the relations of the normal

animal to the substances mentioned, the antennæ were removed from the

socket-cavity.

On the second day after Hauser experimented with the insects, they

exhibited no reaction either against the carbolic acid, the oil of

turpentine, or even against the acetic acid, although he held the glass

rod which had been dipped into it for one or two minutes before and over

the head. The creatures remained completely quiet and immovable, at the

most slightly moving the palpi. They showed otherwise no change in their

mode of life and their demeanor; they ate with great eagerness flesh

which had been placed before them, or dead insects, and some were as

active as usual as late as May. These beetles had, as proved by the

experiments, lost the sense of smell alone; how far the sense of touch

was lost Hauser could not experimentally decide.

The same results followed experiments with species of the genus Ptinus,

Tenebrio, Ichneumon, Formica, Vespa, Tenthredo, Saturnia, Vanessa, and

Smerinthus; also many species of Diptera and Orthoptera, besides Julus

and Lithobius, while many larvæ reacted in the same manner.

Less satisfactory were the experiments with Carabus, Melolontha, and

Silpha; there is no doubt that the species of these genera, through

the extirpation of their antennæ, become more or less injured as to

the acuteness of their powers of smelling; but they never show

themselves wholly unable to perceive strong-smelling substances.

The allurement of the substance acts for a longer time on those

deprived of their antennæ, then they become restless, then they

wander away from the glass tube held before them; still all their

movements are but slightly energetic, and the entire reaction is

indeterminate and enfeebled.

Experiments with the Hemiptera gave still more unfavorable results;

after the loss of their antennæ they reacted to smells as eagerly as

those did which were uninjured.

=Experiments on the use of the antennæ in seeking for food.=—Under this

head experiments were made with Silpha, Sarcophaga, Calliphora, and

Cynomyia.

Silpha and its larva were treated in the following manner: they were

placed in large boxes whose bottoms were covered with moss, etc.; in a

corner of the box was placed a bottle with a small opening, in which was

placed strong-smelling meat. So long as the beetles were in possession

of their antennæ they invariably after a while discovered the meat

exposed in the bottle, while after the loss of their antennæ they did

not come in contact with it.

In a similar way acted the species of Sarcophaga, Calliphora, and

Cynomyia. Hauser, in experimenting with these, placed a dish with a

large piece of decayed flesh on his writing-table. In a short time

specimens of the flies referred to entered through the open window of

the room. The oftener he drove them away from the meat would they swarm

thickly upon it. Then closing the window and catching all the flies, he

deprived them of their antennæ and again set them free. They flew about

the room, but none settled upon the flesh nor tried to approach it.

Where a fly had alighted on a curtain or other object, the decayed flesh

was placed under it so that the full force of the effluvium should pass

over it, but even then no fly would settle upon it.

=Experiments testing the influence of the antennæ of the males in

seeking the females.=—For this purpose Hauser chose those kinds in which

the male antennæ differ in secondary sexual characters from those of the

female, and in which it is known that they readily couple in

confinement, as _Saturnia pavonia_, _Ocneria dispar_, and _Melolontha

vulgaris_. The two first-named insects did not couple after the

extirpation of their antennæ. Of _Melolontha vulgaris_ twenty pairs were

placed in a moderately sized box. On the next morning twelve pairs of

them were found coupling. Hauser then, after removing the first lot,

placed a new set of thirty pairs in the same box, cut off all the

antennæ of the males and those of a number of females. On the following

morning only four pairs were found coupling, and at the end of three

days five others were observed sexually united.

From these experiments Hauser inferred that those insects deprived

of their antennæ were placed in the most favorable situation, such

as they would not find in freedom; for the space in which the

insects moved about was so limited that the males and females must

of necessity meet. But at the same time the results of the

experiments cannot absolutely be regarded as proving that the males,

after the loss of their antennæ, were then not in condition to find

the females, because in the case of the above-mentioned moths, under

similar conditions, after the extirpation of the antennæ no sexual

union took place. If, however, the experiments made do not all lead

to the results desired, Hauser thinks that the results agree with

those of his histological researches, that in the greater number of

insects the sense of smell has its seat in the antennæ. His results

also agree with those of Perris.

=Structure of the organs of smell in insects.=—The olfactory organs

consist, in insects,—_i.e._, all Orthoptera, Termitidæ, Psocidæ,

Diptera, and Hymenoptera, also in most Lepidoptera, Neuroptera, and

Coleoptera,—

1. Of a thick nerve arising from the brain, which passes into the

antennæ.

2. Of a sensitive apparatus at the end, which consists of staff-like

cells, which are modified hypodermis cells, with which the fibres of the

nerves connect.

3. Of a supporting and accessory apparatus, consisting of pits, or peg-

or tooth-like projections filled with a serous fluid, and which may be

regarded as invaginations and outgrowths of the epidermis.

Hauser adds a remark on the distribution of the pits and teeth in the

larvæ of insects, saying that his observations are incomplete, but that

it appears that in the larvæ the teeth are most generally distributed,

and that they occur not on the antennæ alone, but on the palpi; but in

very many larvæ neither pits nor teeth[47] occurred. In the Myriopoda

teeth-like projections occur on the ends of the antennæ. In Lithobius

they form very small, almost cylindrical, pale organs.

[Illustration:

FIG. 268.—Olfactory organ of Caloptenus.

]

[Illustration:

FIG. 269.—Olfactory pits of the antenna of Stenobothrus. This and Fig.

268 after Hauser.

]

LETTERING FOR FIGS. 268, 269, 273, 275, 276, 278–281.—_a_, _a_,

circular thickening of the skin surrounding the opening of the

olfactory pit; _ax_, thread-like continuation of the nerve-cell;

_b_, vesicle-like bottom of the olfactory pit, through which the

olfactory style passes; _br_ bristle in Fig. 283, stout, and

protecting the olfactory pit; _bs_, bent bristle or seta; _ch_,

chitinous integument of the antennæ; _d_, seen in section; _f_,

invaginated pit; _Fv_, Forel’s flask-shaped organ; _Fvo_, its

opening seen from the surface; _gl_, gland-like mass of cells;

_hyc_, hypodermic cells; _i_, entrance into the canal belonging to

the pit; _m_, olfactory membrane; _m′_, _m″_, _mc_, membrane-forming

cell; _n_, nerve of special sense; _nc_, nucleus of the sense- or

ganglion-cell; _o_, opening into the olfactory pit; _p_, olfactory

pit; _cp_, compound pits; _pw_, wall of the pit; _s_, a large seta;

_sc_, sense- or ganglion-cell; _st_, olfactory or sense-style,

sometimes peg-shaped; _tb_, tactile bristle.

[Illustration:

FIG. 270.—_A_, _b_, sense-organ on the abdominal appendages of a fly

(Chrysopila); _c_, sense-organ on the terminal joint of palpus of

Perla.

]

[Illustration:

FIG. 271.—Longitudinal section of part of cercus of _Acheta

domestica_: _ch_, cuticula; _hyp_, hypodermis; _n._ nerve; _h′^1_,

integumental hairs, not sensory; _h^2_, ordinary hair; _h^3_,

sensory hair; _h^4_, bladder-like hair; _sz_, sense-cell.—After Vom

Rath, from Sharp.

]

In the course of a special description of these sense-organs in the

Orthoptera, Hauser describes at length those of _Œdipoda cœrulescens_

and _Caloptenus italicus_. On one antennal joint of Caloptenus (Fig.

268) was often counted 50 pits; on the anterior joints the number

diminishes to about 30. Hauser thinks that in all Orthoptera whose

antennæ are like those of Caloptenus occur similar pits, as he found

them in Stenobothrus (Fig. 269) as well as in Œdipoda. Gryllotalpa

possesses similar pits,—four to six on each antennal joint, making

between 300 and 400 pits on each antenna.[48] In _Mantis religiosa_ the

pits were not detected, but on each joint, except the eighth basal,

there are about 200 small, hollow, curved teeth with a fine opening in

front.

In the Neuroptera (Chrysopa) there occur on the antennæ, besides

numerous very long tactile bristles, small pale, transparent teeth. No

pits could be detected.

In the Hemiptera (two species of Pyrrhocoris only were examined) only

two kinds of tactile bristles occurred, but Hauser detected no pits,

though Lespès states that they are present.

[Illustration:

FIG. 272.—Longitudinal section of apex of palpus of _Pieris brassicæ_:

_sch_, scales; _ch_, cuticula; _hyp_, hypodermis; _n_, nerve; _sz_,

sense-cells; _sh_, sense-hairs.—After Vom Rath, from Sharp.

]

Of the Diptera, Hauser examined more than 60 species. The pits in the

_Diptera brachycera_ (Muscidæ, etc.) are unexceptionally confined to the

third antennal joint. Their number varies extraordinarily in the

different species. _Helophilus florens_ has on each antennal disk only a

single pit, while _Echinomyia grossa_ possesses 200 of them. In flies of

certain families the pits are compound, and contain 10, 20, and often

100 olfactory hairs, partly arising from the coalescence of several

pits. Such pits are usually divided by lateral walls into several

chambers, whose connection is only indicated by their common outlet.

Simple olfactory pits with a single olfactory style were observed only

in the Tabanidæ, Asilidæ, Bombylidæ, Leptidæ, Dolichopidæ, Stratiomyidæ,

and Tipulidæ. In the last the compound forms do not occur at all, but in

the other families mentioned also occur compound pits, receiving from

two to ten nerve-terminations.

The antennal pits of flies are always sac-like invaginations of the

external chitinous integument, of manifold shapes, opening externally

and never closed by a membrane. The pits differ but slightly in the

different species, and that of _Cyrtoneura stabulans_ (Fig. 273) is

described at length as typical of those of brachycerous flies in

general.

The olfactory pits of the Tipulidæ seem to have a somewhat different

structure, since the external passage is closed. It is circular,

surrounded with a slight chitinous wall, and not covered with bristles.

Such pits in their external appearance are like those of the locust

(Caloptenus) and many Hymenoptera. They are situated usually on the

third antennal joint. _Pachyrhina pratensis_ L. has about 60 of them, as

have _Tipula oleracea_ L. and Ctenophora.

In the Lepidoptera, olfactory pits are much like those of flies. Hauser

describes in detail those of _Vanessa io_. Those of the moths were not

examined, but they can be readily and satisfactorily proved to be the

site of the olfactory sense.

[Illustration:

FIG. 273.—Longitudinal section through the third antennal joint of a

fly (_Cyrtoneura stabulans_), showing the compound pits from above

and in section.—After Hauser.

]

[Illustration:

FIG. 274.—Antenna of Adelops, showing the olfactory organs (_p_) in

the five last joints.

]

Historical researches in respect to the Coleoptera generally gave a very

unfavorable result, contrary to Lespès’s views. That author states that

in the Carabidæ the pits are found on the four first joints, but Hauser

could discover them in none which he examined. Usually only tactile

bristles occur, so also in the Cerambycidæ, Curculionidæ, Chrysomelidæ,

and Cantharidæ. In a blind silphid beetle (_Adelops hirtus_) of Mammoth

Cave we have found well-marked olfactory organs (Fig. 274). Similar

organs occur in the antennæ of the Panorpidæ.

Olfactory pits, however, without doubt occur in Silpha, Necrophorus,

Staphylinus, Philonthus, and Tenebrio. The openings of the pits are

small and surrounded with a small chitinous ring; in Silpha,

Necrophorus, and Tenebrio they cannot easily be distinguished from the

insertion-cavities of the bristles, but in Philonthus and Staphylinus

they are less like them, being distinguished by their somewhat larger

size and their often more oval form. In _Philonthus æneus_ about 100

such small pits occur irregularly on the terminal joints; besides, in

this species on each side of the terminal joint is an apparatus which is

like the compound pit generally occurring in the Diptera.

[Illustration:

FIG. 275.—Olfactory pits of the antenna of _Melolontha

vulgaris_.—After Kraepelin.

]

[Illustration:

FIG. 276.—Antennal pit of _Melolontha vulgaris_, seen in vertical

section.—After Hauser.

]

Very remarkable pits occur in the antennal lamellæ of _Melolontha

vulgaris_ (Fig. 275) and other lamellicorns. On the outer surface of the

first and seventh (in the female the sixth) antennal leaf, as also on

the edges of the other leaves, only arise scattered bristles; on the

inner surface of the first and seventh leaves, as also on both surfaces

of the second to sixth leaves, are close rows of rather shallow

depressions of irregular form, some circular, others regularly

hexagonal. Their number is enormous: in the males 39,000, in the females

about 35,000, occur on each antenna.

[Illustration:

FIG. 277.—Organ of smell of Anophthalmus.—After Hauser. _A_, _a_, _b_,

the same in _A. tenuis_, _B_ in _A. tellkampfii_.

]

[Illustration:

FIG. 278.—Section through antennal joint of _Vespa crabro_, showing

the great number of olfactory pits, olfactory and tactile bristles.

_A_, section through an olfactory pit of _Vespa crabro_.—After

Hauser.

]

The antennal pits and teeth of _Dyticus marginalis_ are morphologically

and physiologically identical with those of bees and wasps. In

_Anophthalmus bilimekii_, Hauser found on the last antennal joints about

60 teeth, which essentially differ in form from those previously

described; they are very pale, transparent, cylindrical, elongated, and

bent elbow-shaped on the first third, so that the last two-thirds run

parallel with the antenna. The length of these remarkable teeth is 0.035

mm., their breadth 0.005 mm. He only found them in Anophthalmus, and in

no other species of Carabidæ; they must resemble the teeth described in

Chrysopa. Our species possesses similar processes (Fig. 277). Similar

teeth occur on the maxillary and labial palpi of beetles. _Dyticus

marginalis_ possesses at the end of each terminal palpal joint a group

of very small teeth, which were also detected in _Anophthalmus

bilimekii_, _Melolontha vulgaris_, etc. In _Carabus violascens_ were

detected on the maxillary palpi large, plainly microscopical, white

disks, which are surrounded with a great number of extremely small

teeth.

Whether the above-described organs on the palpi of beetles should be

considered as olfactory or gustatory in their nature can only be

determined by means of physiological experiments; they probably receive

taste-nerve terminations.

[Illustration:

FIG. 279.—Olfactory pits of the antenna of _Vespa vulgaris_.—After

Kraepelin.

]

The Hymenoptera furnished very good material for histological purposes,

so that Hauser could not only study the terminal apparatus of the

olfactory nerves in the perfect insect, but also in three different

stages of the pupa. These are described at length, as regards the

distribution of the pits and teeth, in _Vespa crabro_; each joint of the

antenna (flagellum) possesses between 1300 and 1400 pits, nearly 60

teeth, and about 70 tactile hairs; on the terminal joint there are more

than 200 teeth, so that each antenna has between 13,000 and 14,000

olfactory pits and about 700 teeth (Kegeln). Fig. 278 represents a

cross-section through the penultimate antennal joint of _Vespa crabro_;

we can see how thick are the series of openings on the surface of the

antennæ, and how regular is the distribution of the teeth.

The distribution of the olfactory pits and olfactory teeth is thus seen

to be very general; the deviations are so insignificant that there is no

reason for the establishment of more than one type.

Antennal pits with a small crevice-like opening occur in genera nearly

allied to Vespa and also in most Ichneumonidæ, Braconidæ, and Cynipidæ.

But the crevice-like openings in these families are considerably longer

and often are of a somewhat twisted shape. In all the species with

translucent antennæ we can recognize the inner mouth of the pit as a

round or nearly round disk situated usually under the middle of the

opening. The antennal pits of _Apis mellifica_, as well as those of

Bombus (Fig. 280) and allied genera, differ from those of the

Ichneumonidæ in being not like crevices, but circular openings.

[Illustration:

FIG. 280.—Olfactory pits of the antenna of Bombus.—After Kraepelin.

]

[Illustration:

FIG. 281.—Olfactory pits of the antenna of Formica: _Fv_, Hicks’

“bottle,” Forel’s flask-shaped organ, _Fvo_, its opening.—After

Kraepelin.

]

[Illustration:

FIG. 282.—Supposed olfactory organs at end of antenna of Campodea:

_A_, _C. staphylinus_. _B_, _C. cookei_, from Mammoth Cave.

]

[Illustration:

FIG. 283.—Vertical section through a single olfactory pit in the

antenna of the horse-fly (_Tabanus bovinus_). For lettering see p.

272.—After Hauser.

]

The distribution of the olfactory peg or tooth-like projections seems to

be much more limited than that of the pits in the Ichneumonidæ. Hauser

could not find any. _Apis mellifica_ possesses on each antennal joint

only about twenty slender pale teeth, scarcely a third as many as in

_Vespa crabro_; on the other hand, Formica, of which genus several

species were examined, seems to have far more teeth than pits; they are

relatively long, pale, transparent, and somewhat clavate; they are not

unlike those of Chrysopa; on the terminal joint only occur the round

openings (_Fvo_), which lead into a bottle-shaped invagination of the

integument (_Fv_) and contain an olfactory style (Fig. 281). In the

Tenthredinidæ only teeth and no pits were to be detected. Sirex has on

the under side of the nine last joints of each antenna a group of from

200 to 300 small teeth, which resemble those of _Vespa crabro_; Lyda has

on the terminal joints about 100 teeth. We may add that supposed organs

of smell occur on the antennæ of Campodea (Fig. 282).

Kraepelin also thus briefly summarizes Hauser’s statements as to the

forms of the different organs of smell.

The manifold nature of the antennal organs has, by Hauser, from

thorough studies of the nerve-elements belonging to them, been not

simplified but rendered more complicated. According to this

naturalist we may distinguish the following forms which the

olfactory organs may assume: 1. “Pale, tooth-like chitinous hairs on

the outer surface of the antennæ, which are perforated at the end;

nothing is known as to the relation of the nerve passing into it

(Chrysopa, Anophthalmus). 2. In pit-like depressions of the antennæ

arise _nerve-rods_ (without a chitinous case) which stand in direct

relation with a ganglion-cell lying under it. These pits are either

_simple_, viz. with only an ‘olfactory rod’ (Tabanus, Fig. 283, and

other Diptera, Vanessa), or _compound_ (Muscidæ, and most other

Diptera, and Philonthus). It is important that these pits are partly

_open_ (in the above-named groups of insects), and partly _closed_

and covered with a thin membrane, under whose concavity the

olfactory rods end (Orthoptera, Melolontha, and other lamellicorns).

3. Short, thick pits sunken slightly into the surface of the

antennæ, and over this a chitinous peg perforated at the end, in

whose base, from the interior, projects a very singular nerve-peg,

which is situated over an olfactory ganglion-cell, and provided with

a slender crown of little rods, and flanked on each side by a

flagellum-cell (Hymenoptera). 4. Round or crevice-like pits covered

over by a perforated chitinous membrane with nerve-rods like those

in 3, but in place of the flagellum-cell with ‘membrane-forming’

cells spread before it. Hauser finally mentions further differences

in the ganglion-cells sent out into the nerve-end apparatus. These

exhibit in Diptera and Melolontha only one nucleus, in Hymenoptera a

single very large one (with many nucleoli) and three small ones, in

Vanessa six, in Orthoptera a very large number of nuclei, etc.”

LITERATURE OF THE ORGANS OF SMELL

=Réaumur, Réné Ant. de.= Mémoires pour servir à l’histoire des

insectes. Paris, 1734–42. (i, 283; ii, 224).

=Lesser, F. C.= Insecto-theologia, 1740, p. 262.

=Roesel, A. J.= Insektenbelustigungen, 1746, ii, p. 51.

=Reimarus, H. S.= Allgemeine Betrachtung ueber die Triebe der Thiere

hauptsächlich ihre Kunsttriebe (Instinct). Hamburg, 1760, p. 355.

=Sulzer, J. H.= Die Kenntzeichen der Insecten. Zürich, 1761.

=Lyonet, P.= Traité anatomique de la chenille, 1762, pp. 42, 96, 195.

=Comparetti, A.= De aure interna comparata. Patavii, 1769.

=Bonnet, C.= Œuvres complètes, 1779–1783, ii, p. 36.

—— Contemplation de la nature, Ch. iii, p. 18.

=Scarpa, Ant.= Anatomicæ disquisitiones de auditu et olfactu. Ticini,

1789.

=Huber, F.= Nouvelles observations sur les abeilles, 1792, ii, p. 475.

=Lehrmann, M. C. G.= De antennis insectorum. Londini, Hamburgi, 1799,

p. 48, Diss. posterior; Hamburg and London, 1800, p. 80 (especial

sense, ærocepsis).

=Latreille, P. A.= Histoire naturelle des crustacés et des insectes,

1806–1809, ii, 50.

=Blainville, M. H. D.= Principes d’anatomie comparée, 1822, i, p. 339.

=Dugès, A. L.= Traité de physiologie comparée, 1838, i, p. 161.

=Newport, G.= On the use of the antennæ of insects. (Trans. Ent. Soc.,

London, ii, 1840, pp. 229–248.)

=Robineau-Desvoidy, A. J. B.= Sur l’usage réel des antennes chez les

insectes. (Ann. Soc. Ent. France, 1842, xi Bull., pp. 23–27.)

=Erichson, W. F.= De fabrica et usu antennarum in insectis. Berlin,

1847, 1 Tab., p. 13.

=Perris, E.= Mémoire sur le siège de l’odorat dans les articulés.

(Ann. sc. nat., Sér. 3, 1850, xiv, pp. 159–178.)

=Dufour, L.= Quelques mots sur l’organe de l’odorat et sur celui de

l’ouie dans les insectes. (Actes d. l. Soc. Linn., Bordeaux, 1850,

xvii, Ann. sc. nat., Sér. 3, Zool., xiv, 1850, pp. 179–184.)

=Leydig, F.= Zum feineren Bau der Arthropoden. (Müller’s Archiv, 1855,

pp. 376–480); Lehrbuch der Histologie, 1857, p. 220; Zur Anatomie

der Insekten (Archiv für Anatomie, 1859, pp. 35–89 and 149–183).

—— Ueber Geruchs- und Gehörorgane der Krebse und Insekten. (Archiv f.

Anat. u. Phys., 1860.)

—— Die Hautsinnesorgane der Arthropoden. (Zool. Anzeiger, 1886, pp.

284–291, 308–314, 265–314.)

=Landois, H.= Das Gehörorgan des Hirschkäfers. (Archiv f. mikrosp.

Anat., 1868, iv, pp. 88–95.)

=Troschel, H.= Ueber das Geruchsorgan der Gliedertiere. (Verhandl. d.

naturhist. Vereins d. preuss. Rheinlande u. Westfal., xxvii Jahrg.,

1870, pp. 160–161.)

=Packard, A. S.= The caudal styles of insects sense-organs, _i.e._,

abdominal antennæ. (Amer. Naturalist, 1870, pp. 620, 621. Also Proc.

Bost. Soc. Nat. Hist., 1868, xi, p. 398.)

=Paasch, A.= Von den Sinnesorganen der Insekten im Allgemeinen, von

Gehörund Geruchsorganen im Besondern. (Archiv für Naturgesch., xxxix

Jahrg., i, 1873, pp. 248–275.)

=Chadima, Jos.= Ueber die von Leydig als Geruchsorgane bezeichneten

Bildungen bei den Arthropoden. (Mitteil. d. naturwiss. Ver. f.

Steiermark, 1873, pp. 36–44.)

=Forel, A.= Les Fourmis de la Suisse. (Neue Denkschr. Allg. Schweiz.

Gesellsch. f. d. ges. Naturw., xxvi, 1874, pp. 118, 144.)

—— Études myrmécologiques en 1884, avec une description des organes

sensoriels des antennes. (Bull. Soc. Vaud. sc. nat., 1885, Sér. 2,

xx, pp. 316–380.)

=Graber, V.= Die Insekten. München, 1877.

—— Neue Versuche über die Functionen der Insektenfühler. (Biol.

Centralb., vii, 1887, pp. 13–19.)

=Trouvelot, L.= The use of the antennæ in insects. (Amer. Naturalist,

xi, 1877, pp. 193–196.)

=Mayer, P.= Sopra certi organi di senso nelle antenne dei Ditteri.

(Atti R. Accad. d. Lincei, Roma, Ser. 3, Mem. Cl. sc. fis., mat. e

natur., iii, 1879, p. 11.)

=Hauser, Gustav.= Physiologische und histiologische Untersuchungen

über das Geruchsorgan der Insekten. (Zeitschr. f. wissens. Zool.,

xxxiv, 1880, pp. 367–403, 3 Taf.)

=Kraepelin, Karl.= Ueber die Geruchsorgane der Gliedertiere

(Oster-Programm der Realschule des Johanneums. Hamburg, 1883, pp.

48, 3 Taf.)

=Schiemenz, Paulus.= Ueber das Herkommen des Futtersaftes und die

Speicheldrüsen der Bienen nebst einem Anhange über das Riechorgan.

(Zeitschr. f. wissens. Zool., xxxviii, pp. 71–135, 3 Taf.)

=Plateau, F.= Expériences sur le rôle des palpes chez les arthropodes

maxillés, I., Palpes des insectes broyeurs. (Bull. Soc. Zool.

France, x, 1885, pp. 67–90.)

=Plateau, F.= Une expérience sur la fonction des antennes chez la

Blatte (_Periplaneta orientalis_). (Comptes rend. Soc. Ent. de

Belgique, 1886, pp. 118–122, 1 Fig.)

=Lubbock, J.= On some points in the anatomy of ants. (Monthly Micr.

Journ., 1887, pp. 121–142.)

=Ruland, Franz.= Beiträge zur Kenntniss der antennalen Sinnesorgane

der Insekten. Diss. Marburg, 1888, p. 31, 1 Taf.

=Wasmann, E.= Die Fühler der Insekten. (Stimmen aus Maria-Laach.

Freiburg i. B., 1891, p. 37.)

=Sergi, G.= Ricerche su alcuni organi di senso nelle antenne delle

formiche. (Riv. Filos. Sci. Milano, 1891, p. 10, 3 Figs.)

=Nagel, Wilibald.= Die niederen Sinne der Insekten, 19 Figs.,

Tübingen, 1892, pp. 67.

With the writings of Baster, Lamarck, Cuvier, Treviranus, Oken,

Lefebure, Duméril, Schelver, Bousdorf, Rosenthal, Burmeister,

Slater, Balbiani, Marcel de Serres, Garnier, Berté, Porter, Sazepin,

Reuter, Pierret, Duponchel, Driesch, Küster, Peckham, Lubbock, A.

Dohrn, Lespès.

_c_. The organs of taste

The gustatory organs of insects are microscopic pits or setae, either

hair-like or resembling short pegs, which form the ends of ganglionated

nerves. They are difficult to distinguish morphologically from certain

olfactory structures, and it is owing to their position at or very near

the mouth that they are supposed to be gustatory in nature.

Meinert was the first (1860) to suggest that organs of taste occurred in

ants. He observed in the maxillæ, and tongue of these insects a series

of canals in the cuticula of these organs connected with ganglion-cells,

and through them with the nerves, and queried whether they were not

organs of taste. Forel afterwards (1874) confirmed these observations.

Wolff in an elaborate work (1875) described a group of minute pits (Fig.

284) at the base of the tongue of the honey bee, which he supposed to

possess the sense of smell, but Forel and also Lubbock attributed to

these sensory pits the function of taste. Ten years afterward Will

showed conclusively, both by anatomical studies and by experiments, that

Diptera and Hymenoptera possess gustatory organs. He, however, denied

that the organs of Wolff were gustatory, and maintained that organs of

smell were confined to the maxillæ, paraglossæ, and tongue. As we shall

see, however, what appear to be with little doubt taste-pits, with hairs

or pegs arising from them, are most numerous on the epipharynx of nearly

all insects, and situated at a point where they necessarily must come in

contact with the food as it enters the mouth and passes down the throat.

[Illustration:

FIG. 284.—Taste-pits on the epipharynx (_C_) of the honey-bee: _B_,

horny ridge; _R_, _R_, taste-pits; _L_, _A_, _A_, muscular fibres;

_S_, _S′_, _a b c d e f_, section of skin of œsophagus.—After Wolff.

]

[Illustration:

FIG. 285.—Tip of the proboscis of the honey bee, × 140: _L_, terminal

button or ladle: _Gs_ taste-hairs; _Sh_, guard-hairs; _Hb_, hooked

hairs.—After Will.

]

Kraepelin (1883) discovered taste-organs on the proboscis of the fly,

and taste-hairs at the end of the tongue of the humble-bee (Fig. 285),

and afterwards Lubbock critically discussed the subject, and concluded

that the organs of taste in insects are situated “either in the mouth

itself, or on the organs immediately surrounding it.”

=Structure of the taste-organs.=—The organs have been best studied by

Will, who, besides describing and figuring the chitinous structures,

such as the pits or cups, hairs and the pegs, showed that they were the

terminations of ganglionated nerves.

Figure 286 represents the taste-cups on the maxilla of a wasp, and Fig.

287 the taste-cone or peg projecting from the cup or pit. The cell out

of which the pit and projecting hair or peg are formed is a modified

hypodermis cell; and the seta is apparently a modification of a tactile

hair, situated at the end of a nerve, which just beneath the chitinous

structures passes into a ganglion-cell, which sends off a nerve-fibre to

the main nerve.

Will detected on the tongue of the yellow ant (_Lasius flavus_) from 20

to 24, and in Atta from 40 to 52, of these structures. The number of

pits on the maxillæ vary much, not always being the same on the two

sides of the same insect. We have observed these taste-cups in the honey

and humble bee, not only at the base of the second maxillæ (Fig. 288,

_g_), but also on the paraglossæ (_pg_).

=Distribution in other orders of insects.=—The writer has detected

these taste-cups in other orders than Diptera and Hymenoptera. They

very generally occur in mandibulate insects on the more exposed

surface of the epipharynx (compare pp. 43–46). We have not observed

them in the Synaptera (Lepisma and Machilis).

In the Dermaptera the taste-cups appear to be undeveloped in the

nymph, while in the adult they are fewer in number than in any other

pterygote order yet investigated.

In a species of Forficula from Cordova, Mexico, the taste-pits are

few in number, there being only about a dozen on each side in all;

most of them being situated on the anterior half, and a few near the

base. The taste-pits are provided each with a short fine seta, as

usual arising from the centre.

[Illustration:

FIG. 286.—Under side of left maxilla of Vespa: _Gm_, taste-cups;

_Shm_, protecting hairs; _Tb_, tactile hairs; _Mt_, base of

maxillary palpus.—After Will.

]

In the order Platyptera (including Perla, Pteronarcys, Psocus,

Termes, Eutermes, and Termopsis) we have been unable to detect any

organs of taste.

[Illustration:

FIG. 287.—Section through a taste-cup: _SK_, supporting cone; _N_,

nerve; _SZ_, sense-cell.—After Will. This and Figs. 284–286 from

Lubbock.

]

[Illustration:

FIG. 288.—Tongue of worker honey-bee: _pg_, paraglossæ; _B_, the

same enlarged, showing the taste-papillæ; _C_, _D_, base of a

labial palpus (_mx.′p_) with the taste-papillæ; _E_, taste-cups on

paraglossæ of Bombus; _F_, group of same on left, _G_, on right

side, at base of labial palpus.

]

In the Odonata, however, they are fairly well developed; in

Calopteryx, about 50 taste-cups were discovered; in a species of

Diplax about 28, there being a group of 14 at the base of the

epipharynx on each side of the median line, while in _Æschna heros_

there are two groups of from 25 to 30 taste-cups, situated as in the

two aforenamed genera.

In the Orthoptera the gustatory cups are numerous, well developed,

and present in all the families except the Phasmidæ, where, however,

they may yet be found to occur.

In a large cockroach (Blabera) from Cuba they are well developed. On

each side of the middle of the epipharynx is a curved row of stiff,

defensive spines, and at the distal end of each row is a sensory

field, containing 20 taste-cups on one side and 23 on the other.

Near the front edge of the clypeal region are two more sensory

fields, situated on each side of the median line, there being 35

taste-cups in each field. The taste-cups in this form are rather

smaller than usual in the order.

In the Acrydiidæ they are more numerous than in the Blattidæ. For

example, in _Camnula pellucida_, near what corresponds to the front

edge of the clypeus are two gustatory fields, each bearing about 35

taste-pits. Just in front, under the clypeo-labral suture, are two

similar fields, each containing from 40 to 42 taste-pits. There are

none in front of these. There are thus about 140–150 sense-cups in

all.

The members of the Locustidæ (Fig. 26) appear to be better provided

with the organs of taste than any other Orthoptera, those of the

katydid numbering from 170 to 180. There are from 50 to 60

taste-cups in the front region; behind the middle a group of 25 on

each side, and over an area corresponding to the base of the labrum

and front edge of the clypeus is a sensory field with about 70

taste-cups on each side. They are true cups or beaker-like papillæ,

some with a fine, others with a short, stout, conical seta.

The gustatory organs in the cave cricket (_Hadenœcus subterraneus_,

Fig. 27), from Mammoth Cave, are highly developed, being rounded

papillæ with the nucleus at the top or end. They are grouped on each

side of the middle near the front edge, there being 25 on each side.

An irregular row of these beaker-like organs extends along each

side; some occur under the base of the labrum, but they are most

numerous in a field corresponding to the front edge of the clypeus,

there being 50 on each side, or 100 in all, where in Ceuthophilus

there are only 9 or 10. It would thus appear as if the sense of

taste were much more acute in the cave-dweller than in the

out-of-doors form.

In the Coleoptera taste-cups and setæ are very generally

distributed, though we were unable to detect them in Dendroctonus or

in _Lucanus dama_. As seen in Fig. 57, we have observed numerous

taste-pegs along the maxilla of _Nemognatha lurida_, but otherwise

taste-organs have only been detected in the epipharynx. They not

only occur in the adult beetles, but we have found them in the larvæ

of cerambycid, scarabæid, and other beetles. In the adults

taste-cups appear to be about as well developed in the carnivorous

forms (Carabidæ) as in the phytophagous or lignivorous groups.

In _Chlænius tomentosus_ there are about half as many of these

organs as in Harpalus, while in Calosoma there are 90 taste-cups, 45

on each side, under the base of the labrum. The cups are

papilliform, being rather high, with a seta arising from each.

In the Cicindelidæ, the epipharynx bears a sensory field quite

different from that of the Carabidæ. There are no normal taste-cups,

except a few situated on two large, round, raised areas which are

guarded in front by a few very long setæ. On the surface of each

area are numerous very long setæ which may, if not tactile, have

some other sense, as they arise from cup-like bases or cells. Those

on the outside are like true taste-cups, with a bristle but little

larger than normal in taste-cups generally. We are disposed to

regard this sensory field as a highly specialized gustatory

apparatus.

In the Dyticidæ the taste-cups are nearly as described in the

Carabidæ.

The Staphylinidæ are not well provided with taste-organs. Under the

clypeus of _Staphylinus violaceus_, on each side near the middle, is

a bare rounded area, in which are situated 4 or 5 papilliform

taste-cups, and at the base behind them is another linear group of

about 7 slenderer, somewhat curved, taste-cups. In the Elateridæ

these organs are scantily developed.

In the Buprestidæ (_Buprestis maculiventris_ alone examined) no true

taste-cups were detected. On the other hand, the Lampyridæ are well

supplied with them. Under the clypeus is situated a sensory field

bearing 26 taste-cups, which are rather smaller than usual. Over the

epipharyngeal surface are scattered a few taste-cups, but they are

small and perhaps not gustatory. Under the clypeus of _Lucidota

punctata_ Lec. is a group of 12 taste-cups, and in the middle region

of the epipharynx, situated in a field extending from near the base

to near the front edge, are about 40 taste-cups, which, however, are

not, as is usual, arranged on each side of the median line, but are

scattered among the hairs of the pilose surface of the epipharynx.

In the Cleridæ the taste-cups are few in number.

In the great family of Scarabæidæ, the presence of gustatory organs

is variable. None occur in _Lucanus dama_, though in the June beetle

(_Lachnosterna fusca_ Fröhl.) they are abundantly developed. The

epipharynx bears on each side outside of a spiny area a group of

about 50 taste-cups, each bearing a long seta, those on the outside

of the area passing into a few high, rather slender, papillæ,

without a seta. On the under side of the clypeus is a median group

of 10 taste-cups of singular form, the cups being large, with broad

bases, which posteriorly bear three spines, of which the median one

is the largest.

Taste-cups occur without any known exception in the longicorn

beetles. In _Leptura canadensis_ they are numerous; in _Euryptera

lateralis_ they are abundant along and near the middle of the

anterior half of the labral region, and in _Cyllene robiniæ_ Forst.

(or _pictus_ Drury) they are more numerous than usual, extending in

an unbroken sensory field from near the front margin of the clypeal

region to near the front edge of the epipharynx. The cups vary much

in size, some being one-half as large as others; and those on the

sides of the sensory field bear short, and a few others rather long,

bristles, showing that the taste-cups are modified tactile bristles.

The Tenebrionidæ are fairly well endowed with taste-cups, their

number in _Eleodes obsoleta_ Say amounting to 30 or 40.

Those of the Meloidæ especially are unusual in size and number.

[Illustration:

FIG. 289.—Epipharynx (_ep_) of Nemognatha: _cl_, clypeus; _gh_,

gathering hairs; _tc_, triangular sensory field dotted with taste

cups; _A_, the field enlarged.

]

In _Nemognatha lurida_ Lec. (Fig. 289) the front edge of the

epipharynx contains about 80 remarkably small taste-cups, arranged

irregularly in a triangular sensory space, and not more than ¼ to ⅙,

as large as those on the maxillæ of the same beetle. Unless the

former structures are gustatory it is difficult to account for their

presence here, and it will be observed that the taste-cups in

Epicauta are unusually abundant. Thus in the middle and near the

front of the epipharynx of the blister-beetle over 100 gustatory

cups were counted. They are conical, papilliform, and truncated at

the end as if open, the edge of the opening being ragged, though

bearing no bristle, except in a few cases. Around the edge of the

sinus, on the under side of the labrum, is a regular marginal row of

large, longer, more distinctly chitinized taste-cups, whose walls

are streaked up and down by chitinous thickenings. In _E. callosa_

Lec. there are about 55 taste-cups under the labrum, besides about

10 cells, which may be gustatory structures, situated on either side

of a median setose ridge which passes back under the clypeal region.

The taste-cups of the leaf-beetles are fairly numerous, judging from

an examination of _Diabrotica vittata_. The surface of the

epipharynx is pilose, but the median region is naked, and on the

anterior half bears from 11 to 12 taste-cups, arranged each side of

the median line in a rude Y. On each side, at the base of the labial

region, are two sensitive fields, each bearing about 25 to 26

taste-cups. More were seen under the clypeus.

In the Neuroptera unmistakable taste-cups are not always present. In

_Sialis infumata_ along the median line of the epipharynx and near

the front are about 20 scattered gustatory pegs, which are minute,

but longer and more acute than usual. In _Chauliodes maculatus_

there are one or two taste-cups under the front edge of the clypeus;

others are scattered along the middle from the base of the labrum to

the front, but are not arranged in definite order. In _Corydalis

cornutus_ no sense-cups, pits, or rods are present. In Chrysopa

there are scattered cups armed with a short acute bristle, which are

possibly gustatory in function. In _Myrmeleon diversum_ also the

presence of sense-pits or of taste-cups is doubtful, though a group

of about 12 pits on each side of the clypeal region of the

epipharynx, and a few situated at the base of the labral region, may

be endowed with the sense of taste. In _Mantispa brunnea_, however,

along the middle of the epipharynx are scattered about 30

unmistakable taste-cups, each bearing a short, fine hair.

In the Mecoptera (_Panorpa debilis?_) taste-cups, giving rise to a

minute hair, occur on the labium in two regions, and also on the

maxillæ situated on the stipes near the base of the palpi, and on

the lacinia and galea. They are also to be found on the maxillæ of

_Boreus californicus_, but were not detected on the labium.

They were first detected by Reuter in various microlepidoptera, and

occur on the “basal spot” of the palpi of many butterflies. In a

Tineid moth (_Coleophora coruscipennella_) we have detected what we

suppose to be a group of four taste-pits on the inner side of the

basal joint of the labial palpi.

=Experimental proof.=—No one, says Lubbock, who has ever watched a bee

or wasp can entertain the slightest doubt as to their possession of the

sense of taste. “Forel mixed morphine and strychnine with some honey,

which he offered to his ants. Their antennæ gave them no warning. The

smell of the honey attracted them, and they began to feed; but the

moment the honey touched their lips they perceived the fraud.”

Will at first fed wasps with sugar, so that they frequently visited it;

afterwards he substituted alum for the sugar. Eagerly flying to it, they

had scarcely touched it when they drew back from the distasteful

substance with the most comical gestures, and cleaned their tongues by

frequently running them in and out, repeatedly stroking them with their

fore feet. He noticed a great repugnance to quinine in nearly all the

insects experimented on. Bees and wasps were observed to have a more

delicate gustatory sense than flies, etc., which are more omnivorous in

their tastes.

LITERATURE ON THE ORGANS OF TASTE

=Meinert, F.= Bidrag til de danske myrers naturhistorie. (Kgl. Dansk

Vidensk. selsk. skrifter. Kjoebenhavn. Raekke 5 Naturvid. og math.

Afd., v, 1861, pp. 273–340.)

=Wolff, O. J. B.= Das Riechorgan der Biene. (Nova acta d. K.

Leop.-Carol. Akad., xxxviii, 1875, pp. 1–251, 8 Taf.)

=Joseph, G.= Zur Morphologie des Geschmacksorganes bei Insekten.

(Amtlicher Bericht der 50. Versammlung deutscher Naturforscher und

Aerzte in München, 1877, pp. 227–228.)

=Künckel et Gazagnaire.= Du siège de la gustation chez les insectes

Diptères. Constitution anatomique et physiologique de l’epipharynx

et l’hypopharynx. (Comptes-rend. Acad. Sc., Paris, 1881, xcv, pp.

347–350.)

—— Recherches sur l’organisation et le développement des Diptères et

en particulaire des Volucelles, i, 1875, ii, 1881, 26 Pls.

=Kraepelin, K.= Zur Kenntniss der Anatomie und Physiologie des Rüssels

von Musca. (Zeitschr. f. wissens. Zool., xxxix, 1883, pp. 683–719, 2

Taf.)

=Kirbach, P.= Ueber die Mundwerkzeuge der Schmetterlinge. (Zool.

Anzeiger, 1883, pp. 553–558, 2 Figs.)

=Will, F.= Das Geschmacksorgan der Insekten. (Zeitschr. f. wissens.

Zool., 1885, xlii, pp. 674–707, 1 Taf.)

=Gazagnaire, J.= Du siège de la gustation chez les insectes

Coléoptères. (Comptes-rend. Acad. Sc., Paris, 1886, cii, pp.

629–632; Ann. Soc. Ent. France, Sér. 6, Bull., pp. 79–80.)

=Forel, A.= Expériences et remarques critiques sur les sensations des

insectes. 2^{me} Part. (Recueil Zool. Suisse, iv, 1887, pp.

161–240.)

=Reuter, Enzio.= Ueber den “Basalfleck” auf den Palpen der

Schmetterlinge. (Zool. Anzeiger, 1888, pp. 500–503.)

—— Ueber die Palpen der Rhopaloceren, etc., 6 Taf. Helsingfors, 1896,

pp. 1–578. (Acta Soc. Sc. Fennicæ, xxii, 1896.)

=Packard, A. S.= On the occurrence of organs, probably of taste, in

the epipharynx of the Mecoptera (Panorpa and Boreus). (Psyche, 1889,

v, pp. 159–164.)

—— Notes on the epipharynx, and the epipharyngeal organs of taste in

mandibulate insects. (Psyche, 1889, v, pp. 193–199, 222–228.)

Also Lubbock’s Senses, etc., of animals, and the writings of Briant,

Breithaupt (titles on p. 85).

_d._ The organs of hearing

Although it has been denied by Forel that insects have the sense of

hearing, yet the majority of writers and experimenters agree that

insects are not deaf. On general grounds if, as we know, many insects

produce sounds, it must follow that they have ears to hear, for there is

every reason to suppose that the sounds thus made are, as in other

animals, either for attracting the sexes, for a means of communication,

or to express the emotions. We will begin by briefly describing the

structures now generally supposed to be auditory in function, and about

which there can be no reasonable doubt, and then consider the more

problematical organs, closing with an account of the extremely various

means of producing sounds and cries.

=The ears or tympanal and chordotonal sense-organs of Orthoptera and

other insects.=—The ears or tympana of locusts (Acrydiidæ) are situated

one on each side, on the basal joint of the abdomen, just behind the

first abdominal spiracle. That this is a true ear was first suggested by

J. Müller, and his opinion was confirmed by Siebold, Leydig, Hensen,

Graber, Schmidt, Lubbock, etc.[49]

[Illustration:

FIG. 290.—Ear of a locust (_Caloptenus italicus_), seen from the inner

side: _T_, tympanum; _TR_, its border; _o_, _u_, two horn-like

processes; _bi_, pear-shaped vesicle; _n_, auditory nerve; _ga_,

terminal ganglion; _st_, stigma; _m_, opening, and _m′_, closing,

muscle of the same; _M_, tensor muscle of the tympanum

membrane.—After Graber.

]

The apparatus consists of a tense membrane, the _tympanum_, surrounded

by a horny ring (Fig. 290). “On the internal surface of this membrane

are two horn-like processes (_o_, _u_), to which is attached an

extremely delicate vesicle (_bi_) filled with a transparent fluid, and

representing a membranous labyrinth. This vesicle is in connection with

an auditory nerve (_n_) which arises from the third thoracic ganglion,

forms a ganglion (_ga_) upon the tympanum, and terminates in the

immediate neighborhood of the labyrinth by a collection of cuneiform,

staff-like bodies, with very finely pointed extremities (primitive

nerve-fibres?), which are surrounded by loosely aggregated ganglionic

globules” (Siebold’s Anatomy of the Invertebrates).

[Illustration:

FIG. 291.—Fore tibia of _Locusta viridissima_. _td_, cover of the

drum; _tr_, fissure between the drum and its cover.—After Graber,

from Lang.

]

In the green grasshoppers, katydids, and their allies, the ears are

situated on the fore tibiæ, where these organs can be found after a

careful search (Figs. 291, 292).

The presence of the structure is indicated by the oval disc, the drum,

which is a thin tense membrane covering the auditory apparatus of

nerves, ganglion cells, and auditory rods beneath.

The tympana, or drums, are not present in all Locustidæ and

Gryllidæ, and, as Lubbock states, it is an additional reason for

regarding them as auditory organs, that in those species which

possess no stridulating organs the tympana are also wanting. In many

of the Locustidæ the tympana are covered or protected by a fold of

the skin projecting over them. These covered ones are, Graber

thinks, derived from the open ones.

[Illustration:

FIG. 292.—_A_, fore tibia of a European grasshopper (Meconema),

containing the ear: _Ty_, tympanum or outer membrane; _Tr_ 1, _Tr_

2, tracheæ. _B_, diagrammatic cross-section through the tibia and

ear of the same; _Ty_, tympanum; _Ct_, cuticula; _CM_, hypodermis:

_A_, the auditory organ connecting with the tympanum; _B_,

supra-tympanal auditory organ; _GZ_, the ganglion-cell belonging

to them; _Hst_, the auditory rod connecting with the

ganglion-cells.—After Graber, from Judeich and Nitsche.

]

On examining the apparatus within the leg under the drum, it is seen to

consist of the trachea, the auditory vesicles and rods, ganglion cells,

and acoustic nerve. The trachea is greatly modified (Fig. 292, _Tr_ 1).

On passing into the tibia the trachea enlarges and divides into two

branches, which reunite lower down. The spiracles supplying the air to

this enlarged trachea are considerably enlarged, while in the dumb

species it is of the normal size. The enlarged trachea passes close to

the tympanum, which thus has air on both sides of it: the open air on

the outer, the air of the trachea on its inner surface. In fact, as

Lubbock states, “the trachea acts like the Eustachian tube in our own

ear; it maintains an equilibrium of pressure on each side of the

tympanum, and enables it freely to transmit the atmospheric vibrations.”

[Illustration:

FIG. 293.—The auditory apparatus in the tibia of a grasshopper,

showing the tympanal nerve-endings in situ: _EBI_, terminal vesicles

of Siebold’s organ; _SN_, nerve of the organ of Siebold; _Gr_, group

of vesicles of same; _SO_, nerve-endings of the same; _vT_, front

tympanum; _vTr_, front branch of the trachea; _hT_, hinder tympanum;

_hTr_, hinder branch of the trachea; _Sp_, space between the

tracheæ; _go_, supra tympanal ganglion; _rN_, connecting

nerve-fibrils between the ganglion cells and the terminal vesicles;

_R_, upper, _n-S_, lower, root of the transparent covering membrane.

(Other lettering not explained by author.)—After Graber.

]

[Illustration:

FIG. 294.—Auditory rod of _Gryllus viridissimus_: _fd_, auditory rod;

_ko_, terminal piece.—After Graber, from Lubbock.

]

These tracheæ, says Graber, though formed on a similar plan, present

many variations, corresponding to those of the tympana, and showing

that the tympana and the tracheæ stand in intimate connection with

one another. For instance, in those species where the tympana are

equal, the tracheæ are so likewise; in Gryllotalpa, where the front

tympanum only is developed, though both tracheal branches are

present, the front one is much larger than the other; and where

there is no tympanum, the trachea remains comparatively small, and

even in some cases undivided (Lubbock, _ex_ Graber).

The acoustic nerve, which next to the optic is the thickest in the body,

divides soon after entering the tibia into two branches, one almost

immediately forming a ganglion, the supra-tympanal ganglion, the other

passing down to the tympanum, where it expands into an elongated flat

ganglion, the organ of Siebold (Fig. 293), and closely applied to the

anterior tracheæ.

At the upper part of the ganglion is a group terminating below in a

single row of vesicles, the first few of which are approximately equal,

but which subsequently diminish regularly in size. Each of these

vesicles is connected with the nerve by a fibril (Fig. 293, _vN_), and

contains an auditory rod (Fig. 294). They are said by Graber to be

brightly refractive, hollow (thus differing from the retinal rods, which

are solid), and terminate in a separate end-piece (_ko_). The rods were

first discovered by Siebold, and, as Lubbock remarks, may be regarded as

specially characteristic of the acoustic organs of insects.

[Illustration:

FIG. 295.—Chordotonal organ in nymph of a white ant.—After Müller,

from Sharp.

]

[Illustration:

FIG. 296.—Right half of 8th body-segment of _Corethra plumicornis_:

_g_, ganglion of ventral cord; _lm_, longitudinal muscle; _cn_,

chordotonal nerve; _cl_, chordotonal ligament; _cg_, chordotonal

ganglion; _cs_, rod of chordotonal organ; _cst_, terminal cord;

_tb_, tactile setæ; _hn_, out-going fibres of the integumental

nerves.—After Graber, from Lang.

]

As will be seen in Fig. 293, at the upper part of the tibial organ

of Ephippigera there is a group of cells, and below them a single

row of cells gradually diminishing in size from above downwards.

“One cannot but ask oneself,” says Lubbock, “whether the gradually

diminishing size of the cells in the organ of Siebold may not have

reference to the perception of different notes, as is the case with

the series of diminishing arches in the organ of Corti of our own

ears.”

These organs were supposed to be restricted to the Orthoptera, but

in 1877 Lubbock discovered what seems to resemble the supra-tympanal

auditory organ of Orthoptera in the tibia of the yellow ant (_Lasius

flavus_). Graber confirmed Lubbock’s account, and also discovered

these organs in the tibia of a Perlid (_Isopteryx apicalis_), and

Fritz Müller has detected them in the fore tibiæ of the nymph of

_Calotermes rugosus_ (Fig. 295). To these structures Graber gave the

name of chordotonal organs.

He has also detected these organs in all the legs of other insects

(Trichoptera, Pediculidæ), and auditory rods have been discovered in

the antennæ of Dyticus and of Telephorus by Hicks, Leydig, and

Graber. Graber classifies the chordotonal organs into truncal and

membral. In Coleoptera and Trichoptera they may occur on several

joints of the leg; others are more localized,—thus he distinguishes

femoral (Pediculidæ), tibial (Orthoptera, Perlidæ, Formicidæ), and

tarsal organs (Coleoptera).

A type of chordotonal organ, observed in the body-segments of the

larvæ of several insects by Leydig, Weismann, Graber, Grobben, and

Bolles Lee, is to be seen in the transparent larva of Corethra (Fig.

296), where the auditory organ extends to the skin. It contains at

the point _cs_ two or three auditory rods. In the opposite direction

a fine ligament (_cl_) passes from _cg_ to the skin; in this way the

auditory organ is suspended in a certain state of tension, and is

favorably situated to receive even very fine vibrations. A similar

apparatus has been detected in the larva of Ptychoptera.

=Antennal auditory hairs.=—It is not at all improbable that the antennæ

of different insects contain auditory as well as olfactory structures.

Lubbock has suggested that the singular organs which have only been

found in the antennæ of ants and certain bees, and to which he gives the

name of “Hicks’ bottles” (Fig. 281), may act as microscopic

stethoscopes, while Leydig also regards them as chordotonal organs.

That, however, some of the antennal hairs of the mosquito, as first

suggested by Johnson and afterwards proved experimentally by Mayer, are

auditory, seems well established. Fastening a male mosquito down on a

glass slide, Mayer then sounded a series of tuning-forks. With an Ut_{4}

fork of 512 vibrations per second, some of the hairs were seen to

vibrate vigorously, while others remained comparatively at rest. The

lower (Ut_{3}) and higher (Ut_{5}) harmonics of Ut_{4} also caused more

vibration than any intermediate notes. These hairs, then, are specially

tuned so as to respond to vibrations numbering 512 per second. Other

hairs vibrated to other notes, extending through the middle and next

higher octave of the piano.

Mayer then made large wooden models of these hairs, the one

corresponding to the Ut_{3} hair being about a metre in length, and on

counting the number of vibrations they made when they were clamped at

one end and then drawn on one side, he found that it “coincided with the

ratio existing between the numbers of vibrations of the forks to which

covibrated the fibrils,” or hairs. It should be observed that the song

of the female mosquito corresponds nearly to this note, and would

consequently set the hairs in vibration. Mayer observed that the song of

the female vibrates the hairs of one of the antennæ more forcibly than

those of the other. Those auditory hairs are most affected which are at

right angles to the direction from which the sound comes. Hence from the

position of the antennæ and the hairs a sound will be loudest or most

intense if it is directly in front of the head. If, then, the song of

the female affects one antenna more than another, the male turns his

head until the two antennæ are equally affected, and is thus able to fly

straight towards the female. From his experiments Mayer found that the

male can thus guide himself to within 5° of the direction of the female.

Hence he concludes that “these insects must have the faculty of the

perception of the direction of sound more highly developed than in any

other class of animals.” (Also see Child’s work.)

=Special sense-organs in the wings and halteres.=—Organs of a

special sense, which Hicks supposed to be those of smell, were found

by him near or at the base of the wings of Diptera, Coleoptera, and

less perfect ones in Lepidoptera, Neuroptera, and Orthoptera, with a

trace of them in Hemiptera; but these were considered by Leydig to

be auditory organs, since he found the nerves to end in club-shaped

rods, like those of Orthoptera.

Hicks found, as to the halteres and their sense-organs, that the

nerve in the halter is the largest in the insect, except the optic

nerve; and that at the base of the halteres is a number of vesicles

arranged in four groups, to each of which the nerve sends a branch.

Afterwards Bolles Lee discovered that the vesicles, undoubtedly

perforated, contain a minute hair, those of the upper groups being

protected by hoods of chitin. He regarded them as olfactory organs,

while Lubbock seems inclined to consider them as auditory

structures. Graber also regards the vesicles of Hicks as chordotonal

organs.

In his elaborate account of the balancers, Weinland concludes that

the organs of sense of varying structure occurring at the base of

these appendages allow the perception of movements which the

halteres perform and which enable the fly to steer or direct its

course. The halteres can thus cause differences in the direction of

the flight of a fly in the vertical plane. If the balancers act

unequally, there is a change in direction.

_e._ The sounds of insects

Insects have no true voice; but sounds of different intensity, shrill

cries, and other noises are produced mechanically by insects, either

being love-songs to attract the sexes, to give signals, to communicate

intelligence, or perhaps to express the emotions. The loud, shrill cry

of the Cicada, or chirp of the cricket, is evidently a love-call, and

results in the mating of individuals of separate broods more or less

widely scattered, thus preventing too close interbreeding.

The simplest means of making a noise is that of the death-watch

(Anobium), which strikes or taps on the wall with its head or abdomen.

Longicorn beetles make a sharp sound by the friction of the

mesoscutellum against the edge of the prothoracic cavity, the head being

alternately raised and lowered, Burying-beetles (Necrophorus) rub the

abdomen against the hinder edges of the elytra. Weevils make a loud

noise by rapidly rubbing the tips of the abdomen on the ends of the

elytra.

Landois offers the following summary of the kinds of noises produced

by beetles:

1. Tapping sounds (Bostrycinæ, Anobium).

2. Grating sounds (Elateridæ).

3. Friction without special rasping organs (_Euchirus

longimanus_).

4. Rasping sounds produced by friction:

_a._ Rubbing of the pronotum on the mesonotum (Cerambycidæ

except Spondyli and Prionus).

_b._ Friction of the prosternum on the mesosternum (_Omaloplia

brunnea_).

_c._ Elytra with a rasp at the end (Curculionidæ, Dyticidæ,

Pelobius).

_d._ With a coxal rasp (Geotrupes, Ceratophyus). The male of

Ateuchus stridulates to encourage the female in her work, and

from distress when she is removed. (Darwin.)

_e._ Friction of the edge of the elytra against the femur

(_Chiasognathus grantii_).

_f._ Pygidium with two rasps in the middle (Crioceris, Lema,

Copris, Oryctes, Necrophorus, Tenebrionidæ).

_g._ Abdomen with a grating ridge and four grating plates

(Trox).

_h._ Abdomen with two toothed ridges rubbing on a rasp on edge

of wing-cover (Elaphus, Blethisa, Cychrus).

_i._ Rubbing the elytra on a rasp on the hind wings (_Pelobius

hermanni_).

_j._ Friction of the wing against the abdominal segments

(_Melolontha fullo_).

Mutilla makes a rather sharp noise by rubbing one abdominal segment

against another. Ants (Ponera) have a stridulating apparatus, and

other genera numerous (20) ridges between the segments.

Even certain moths and butterflies emit a rasping or crackling

noise. The death’s-head moth and other sphinges cause it by rubbing

the palpi against the base of the proboscis. These and certain

butterflies are provided with parallel ridges forming a rasp on the

“basal spot” of the inner side of the basal joint of each palpus

(Reuter). A South American butterfly (_Ageronia feronia_) can be

heard for several yards as it flies with a crackling sound. Hampson

finds that the cause of the clicking sound is due to a pair of

strong chitinous hooks attached to the thorax, against which play

the spatulate ends of a pair of hooks attached to the fore wings. An

Australian moth (Hecatesia) flies with a whizzing sound; Vanessa is

said to be sonorous.

The males of Orthoptera produce their shrill cries or chirping

noises, 1, by rubbing the thighs against the sides of the body

(Acrydiidæ); 2, by the friction of the base of the fore wings on

each other (Locustidæ); 3, by rubbing the base of the upper on the

base of the hinder or under pair (Gryllidæ), in the two last there

being a shrilling apparatus consisting of a file on the hind wings,

which rubs on a resonant surface on the fore wings. The females are

not invariably dumb, both sexes of the European Ephippigera being

able to faintly stridulate. Corixa also produces shrill chirping

notes. (Carpenter.)

Certain insects also hum, and have what may perhaps be called a voice.

The cockchafer, besides humming with the wings, produces a sound almost

like a voice. In the large trachea, just behind each spiracle, is a

chitinous process, which is thrown into vibrations by the air during

respiration, and thus produces a humming noise. (Lubbock.) Such is also

the case with flies, the mosquito, dragon-flies, and bees. In flies and

dragon-flies the “voice” is caused by the air issuing from the thoracic

spiracles; while in the humble-bee the abdominal spiracles are also

musical. The sound made by the spiracles bears no relation to that

caused by the wings. Landois tells us that the wing-tone of the

honey-bee is A′; its voice, however, is an octave higher, and often goes

to B″ and C″.

The sounds produced by the wings are constant in each species, except

where, as in Bombus, there are individuals of different sizes; in these

the larger ones generally give a higher note. Thus the comparatively

small male of _Bombus terrestris_ hums on A′, while the large female

hums an entire octave higher.

From the note produced the rapidity of the vibrations can be calculated.

For example, the house-fly, which produces the sound of F, vibrates its

wings 21,120 times in a minute, or 335 times in a second; and the bee,

which makes a sound of A′, as many as 26,400 times, or 440 times in a

second. On the contrary, a tired bee hums on E′, and therefore,

according to theory, vibrates its wings only 330 times in a second.

Marey has confirmed these numbers graphically, and found by experiment

that the fly actually makes 330 strokes in a second. (Lubbock.)

A different kind of musical apparatus is that of the cicada, which has

been elaborately described by Graber. The shrill, piercing notes issue

from a pair of organs on the under side of the base of the abdomen of

the male, these acting somewhat as two kettle-drums, the membrane

covering the depressions being rapidly vibrated.

LITERATURE ON THE ORGANS OF HEARING

_a._ The auditory organs

=Siebold, C. Th. E. von.= Ueber das Stimm- und Gehörorgan der

Orthopteren. (Archiv f. Naturgesch., 1844, x, pp. 52–81.)

A Text-book of Entomology Including the Anatomy, Physiology, Embryology and Metamorphoses of Insects for Use in Agricultural and Technical Schools and Colleges as Well as by the Working Entomologist · 第 6 / 16 章

Looking at the eye as a whole, Hickson regards all the nerve structure