Part 1

# An Introduction to Entomology: Vol. 4: or Elements of the Natural History of the Insects ### By Kirby, William

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[Illustration: _Painted by J. J. Masquerier._

_Engraved by W. T. Fry._

_William Spence, Esq^r., F.L.S._]

_Published by Longman & C^o. London, July 1825._

AN INTRODUCTION TO ENTOMOLOGY:

OR ELEMENTS OF THE _NATURAL HISTORY OF INSECTS_:

WITH PLATES.

BY WILLIAM KIRBY, M.A. F.R. AND L.S. RECTOR OF BARHAM, AND WILLIAM SPENCE, ESQ. F.L.S.

IN FOUR VOLUMES. VOL. IV.

_FIFTH EDITION._

LONDON: PRINTED FOR LONGMAN, REES, ORME, BROWN, AND GREEN, PATERNOSTER ROW.

1828.

PRINTED BY RICHARD TAYLOR, RED LION COURT, FLEET STREET.

CONTENTS OF VOL. IV.

Letter. Page.

XXXVII. Internal Anatomy and Physiology of Insects. _Sensation_ 1-33

XXXVIII. Internal Anatomy and Physiology of Insects continued. _Respiration_ 34-80

XXXIX. Internal Anatomy and Physiology of Insects continued. _Circulation_ 81-101

XL. Internal Anatomy and Physiology of Insects continued. _Digestion_ 102-126

XLI. Internal Anatomy and Physiology of Insects continued. _Secretion_ 127-151

XLII. Internal Anatomy and Physiology of Insects continued. _Reproduction_ 152-173

XLIII. Internal Anatomy and Physiology of Insects concluded. _Motion_ 174-203

XLIV. Diseases of Insects 204-240

XLV. Senses of Insects 241-264

XLVI. Orismology, or Explanation of Terms 265-363

XLVII. System of Insects 364-428

XLVIII. History of Entomology 429-485

XLIX. Geographical Distribution of Insects; their Stations and Haunts; Seasons; Times of Action and Repose 486-527

L. On Entomological Instruments; and the best Methods of collecting, breeding, and preserving Insects 528-559

LI. Investigation of Insects 560-573

Appendix 575-584 Authors quoted 585-602 Explanation of the Plates 603-614 Indexes 615-683

AN INTRODUCTION TO ENTOMOLOGY.

LETTER XXXVII.

_INTERNAL ANATOMY AND PHYSIOLOGY OF INSECTS._

SENSATION.

Having given you this full account of the _external_ parts of insects, and their most remarkable variations; I must next direct your attention to such discoveries as have been made with regard to their _Internal Anatomy and Physiology_: a subject still more fertile, if possible, than the former in wonderful manifestations of the POWER, WISDOM and GOODNESS of the CREATOR.

The vital system of these little creatures, in all its great features, is perfectly analogous to that of the vertebrate animals. _Sensation_ and _perception_ are by the means of _nerves_ and a _common sensorium_; the _respiration_ of air is evident, being received and expelled by a particular apparatus; _nutrition_ is effected through a _stomach_ and _intestines_; the analogue of the _blood_ prepared by these organs pervades every part of the body, and from it are secreted various peculiar substances; _generation_ takes place, and an intercourse between the sexes, by means of appropriate _organs_; and lastly, _motion_ is the result of the action of _muscles_. Some of these functions are, however, exercised in a mode apparently so dissimilar from what obtains in the higher animals, that upon a first view we are inclined to pronounce them the effect of processes altogether peculiar. Thus, though insects respire _air_, they do not receive it by the _mouth_, but through little orifices in the _sides_ of the body; and instead of _lungs_, they are furnished with a system of air-vessels, ramified _ad infinitum_, and penetrating to every part and organ of their frame; and though they are nourished by a fluid prepared from the food received into the stomach, this fluid, unlike the blood of vertebrate animals, is _white_, and the mode in which it is distributed to the different parts of the system, except in the case of the true _Arachnida_, in which a circulation in the ordinary way has been detected, is altogether obscure.

In order that you may more clearly understand the variations that occur in insects, and in what respects they differ amongst themselves, and from the higher animals, in the vital functions and their organs, I shall consider them as to their organs of _sensation_, _respiration_, _circulation_, _nutrition_, _generation_, _secretion_, and _muscular motion_.

* * * * *

_Organs of Sensation._--The nervous system of animals is one of the most wonderful and mysterious works of the CREATOR. Its pulpy substance is the _visible_ medium by which the governing principle[1] transmits its commands to the various organs of the body, and they move instantaneously--yet this appears to be but the conductor of some higher principle, which can be more immediately acted upon by the mind and by the will. This principle, however, whatever it be, whether we call it the nervous _fluid_, or the nervous _power_[2], has not been detected, and is known only by its effects. The system of which we are speaking may therefore be deemed the foundation and root of the animal, the centre from which emanate all its powers and functions.

Comparative anatomists have considered the nervous system of animals as formed upon _four_ primary types, which may be called the _molecular_, the _filamentous_, the _ganglionic_, and _cerebro-spinal_[3]. The _first_ is where invisible nervous molecules are dispersed in a gelatinous body, the existence of which has only been ascertained by the nervous irritability of such bodies, their fine sense of touch, their perceiving the movements of the waters in which they reside, and from their perfect sense of the degrees of light and heat[4]. Of this description are the infusory animals, and the _Polypi_. The nervous molecules in these are conjectured to constitute so many ganglions, or centres of sensation and vitality[5]. The _second_, the filamentous, is where the nervous system consists of nervous threads radiating from the mouth, as in the _Radiata_, or star-fish and sea-urchins[6]. The _third_, the ganglionic, is where the nervous system consists of a series of ganglions connected by nervous threads or a medullary chord, placed, except the first ganglion, below the intestines, from which proceed nerves to the various parts of the body. This system may be considered as divisible into two--the _proper ganglionic_, in which it is ganglionic with the ganglions arranged in a series with a double spinal chord. This prevails in the classes _Insecta_, _Crustacea_, _Arachnida_, &c., and the _improper ganglionic_, in which it is ganglionic with the ganglions dispersed irregularly, but connected by nervous threads, as in the _Mollusca_[7]. In the _fourth_, the cerebro-spinal, the nervous tree may be said to be double, or to consist of _two_ systems--the first taking its origin in a brain formed of two hemispheres contained in the cavity of the head, from which posteriorly proceeds a spinal marrow, included in a dorsal vertebral column. These send forth numerous nerves to the organs of the senses and the muscles of the limbs. The second consists of two principal ventral chords, which by their ganglions, but without any direct communication, anastomose with the spinal nerves and some of those of the brain, and run one on each side from the base of the skull to the extremity of the _sacrum_. This system consists of an assemblage of nervous filaments bearing numerous ganglions, from which nervous threads are distributed to the organs of nutrition and reproduction[8]. Its chords are called the _great sympathetic_, the _intercostal_, or _trisplanchnic_ nerves[9]. While the first of these two systems is the messenger of the will, by means of the organs of the senses connects us with the external world, and is subject to have its agency interrupted by sleep or disease[10]; the latter is altogether independent of the will and of the intellect, is confined to the internal organic life, its agency continues uninterrupted during sleep, and is subject to no paralysis. While the former is the seat of the intellectual powers, the latter has no relation to them, but is the focus from whence _instincts_ exclusively emanate: from it proceed spontaneous impulses and sympathies, and those passions and affections that excite the agent to acts in which the will and the judgement have no concern[11].

It is probable, though the above appear to exhibit the _primary_ types of nervous systems, that others exist of an _intermediate_ nature, with which future investigators may render us better acquainted[12]: but as our business is solely with that upon which _insects_ in this respect have been modelled, without expatiating further in this interesting field, I shall therefore now confine myself to them.

We have before seen[13] that the nervous system of insects belongs to the _ganglionic_ type: but it requires a more full description, and this is the place for it. It originates in a small brain placed in the head, and consisting almost universally of two lobes, sometimes extremely distinct. It is placed over or upon the _œsophagus_ or gullet, and from its posterior part proceeds a double nervous chord, which embracing that organ as a collar dips below the intestines, and proceeds towards the anus, forming knots or ganglions at intervals, in many cases corresponding in number with the segments of the body, and sending forth nerves in pairs, the ramifications of which are distributed to every part of the frame. In the perfect insect the bilobed ganglion of the head or the brain is usually of greater volume than in the larva, and the ganglions of the spinal chord are fewer, which gives a more decided character of _centricity_ to the whole nervous system[14]. This may be considered more particularly with respect to its _substance_ and _colour_; its _tunics_, and _parts_.

I. _Substance and Colour._--The nervous apparatus of insects is stated by those who have examined it most narrowly, though consisting of a cortical and medullary part, the latter more delicate and transparent than the former, to be less tender and less easy to separate than the human brain[15]. It has a degree of tenacity, and does not break without considerable tension; in general, it is clammy and flabby, and under a microscope a number of minute grains are discoverable in it, and when left to dry upon glass, it appears to contain a good deal of oil, which does not dry with the rest[16]. That of the ganglions differs from the substance of the rest of the spinal chord, in being filled with very fine aërial vessels, which are not discoverable in the latter[17]. With regard to _colour_, Lyonet states that the chords of the spinal marrow in the larva of the great goat-moth are of a blueish gray, and have some transparence[18]; Malpighi and Swammerdam observed that the cortical part of the ganglions of that of the silk-worm and the hive-bee had a reddish hue, while the medullary part was white[19]; Cuvier relates that the brain and the third ganglion in _Hypogymna dispar_, with us a scarce moth, differed in colour from all the rest, being quite white, while the others were more or less tinted, and examined under a lens appeared variegated by reddish sinuous markings, resembling blood vessels as they are seen in injected glands[20].

II. _Tunics._--The coats that inclose the various branches of the nervous system in insects seem analogous to those of vertebrate animals. The first thing that strikes the eye, when these parts in a recent subject are submitted to a microscope, is a tissue of very delicate vessels, which ramify beyond the reach of the assisted sight; these are merely air-vessels or _bronchiæ_ derived originally from the _tracheæ_ of the animal: but besides these is an exterior and an interior tunic; the first corresponding with the _dura mater_ of anatomists; and the other, which is the most delicate and incloses the cortical and medullary parts, with the _pia mater_[21].

III. _Parts._--The nervous system of insects consists of the _brain_; the _spinal marrow_ and its _ganglions_; and the _nerves_.

i. _Brain_.[22] Linné denied the existence of a _brain_ in insects, and most modern physiologists seem to be of the same opinion. A part however, analogous to this important organ--at least in its situation, and in its emission of nerves to the principal organs of the _senses_, in which respect it certainly differs very materially from the upper cervical ganglion, which Dr. Virey regards as its analogue[23]--is certainly to be found in them; and as Messrs. Cuvier and Lamarck distinguish this part by the name of _brain_, we may continue to call it by that name without impropriety. The _brain_ of insects, then, is distinguished from the succeeding ganglions of the spinal chord by its _situation_ in the head, the middle of the internal cavity of which it occupies, and by being the only ganglion _above_ the œsophagus. It is usually small, though in some cases larger than they are[24]. It consists of two lobes, more or less distinct and generally of a spherical form. In _Oryctes nasicornis_ and _Pontia Brassicæ_ the lobes are separated both before and behind[25]; while in the larva of _Dytiscus marginalis_, but not in the imago, in which there are two large hemispheres separated by a furrow, the brain is undivided[26]. Cuvier mentions the larva of a saw-fly in which this part is formed of _four_ nearly equal spherical bulbs[27]: in the Scorpion (to judge by the figure of Treviranus[28]) the two lobes represent an equilateral triangle, the exterior angle of which terminates in several lesser spherical bulbs; in _Acrida viridissima_, _Nepa cinerea_, _Clubiona atrox_, and the common Louse, the lobes are pear-shaped[29].

ii. _The spinal marrow and its ganglions_[30]. From the _posterior_ part of the brain of insects, but in the ground and water beetles (_Eutrech_in_a_ and _Eunech_in_a_) from its _sides_ below[31], issue two chords which diverging embrace the _œsophagus_, and dipping below it and the intestines,--a situation they maintain to the end of their course,--and in their further progress uniting at intervals and dilating into several knots or ganglions, compose their spinal marrow. This part is so named, from a supposed analogy to the spinal marrow of vertebrate animals, which however admits of some degree of doubt; yet, since it mixes the functions of that organ with those of the great sympathetic nerves, the denomination is not wholly improper, and may be retained. Though this chord is usually _double_ when it first proceeds from the brain, and surrounds the _œsophagus_ like a collar, yet in some insects it may be called a _single_ chord. This is the case with that of the common louse, in which Swammerdam could perceive no opening for the transmission of the part just named[32]; if he was not mistaken in this, the brain, as well as the rest of the spinal marrow in that animal, would be below the intestines; from the figures of Treviranus it should seem that the spiders, at least _Clubiona atrox_, are similarly circumstanced[33]; in the cheese-maggot, which turns to a two-winged fly (_Tyrophaga Casei_), the chord is also single, but it has a small orifice through which the gullet passes[34]. At the union of the chords in other cases below that organ, a knot or ganglion is usually formed, and an alternate succession of internodes and ganglions commonly follows to the end. The internodes also may generally be stated to consist of a _double_ chord, though in many cases the two chords unite and become one, or are distinguished only by a longitudinal furrow, and even where they are really distinct and separable, in the body of the insect they lie close together[35]. In the rhinoceros beetle (_Oryctes nasicornis_) and _Acrida viridissima_ &c. _all_ the internodes consist of a double chord[36]; but in many other insects numerous variations in this respect occur.--Thus in the stag-beetle the _last_ internode is single[37]; in the caterpillar of the cabbage butterfly (_Pontia Brassicæ_) the _five first_ are double, and the _six last_ single[38]; in that of the great goat-moth (_Cossus ligniperda_) the _three first_ only are double, but the others terminate in a fork[39]; in the cockroaches (_Blatta_) the _four first_, in _Hydrophilus piceus_ the _three first_, and in _Eristalis tenax_ the _two first_ only are double, the rest being all single[40]. A singular variation takes place in _Hypogymna dispar_; _all_ the internodes are single, except the _second_, the chords of which at first are separate, and afterwards united[41]; and, to name no more, in _Clubiona atrox_ there is only _one_ internode, which is single, with a longitudinal furrow[42]. In some, as in the louse, the grub of _Oryctes nasicornis_, and the cheese-maggot, there are no internodes, the spinal marrow being formed of knots separated only by slight or deep constrictions[43].

I must next say something of the _ganglions_[44]. Lyonet has observed that, in the caterpillar of the great goat-moth, these in one respect differ remarkably from the chords that connect them; in the latter the air-vessels or bronchiæ only cover the _outside_ of the tunic, while in the former they enter the _substance_ of the ganglion, which is quite filled with their delicate and numberless branches[45]. Every ganglion may be regarded in some degree as a centre of vitality or little brain[46], and in many cases, as well as the brain, they are formed of two lobes[47]. I shall now consider them more

## particularly as to their _station_, _number_, and _shape_.

1. With regard to the first head, their _station_, they are most commonly divided between the trunk and abdomen; but in some cases, as in _Hydrophilus piceus_ and _Acrida viridissima_, the _first_ ganglion is in the _head_[48]; in others, as in the louse, the water-scorpion, and the grub of the rhinoceros-beetle, they are confined to the _trunk_, their functions in the abdomen being supplied by numerous radiating nerves[49]; in others again, as in the scorpion, they are all _abdominal_. The ganglions vary also in their situation with respect to each other. Thus in some, as in the larva of the Chamæleon-fly (_Stratyomis Chamæleon_), they are so near as to appear like a string of beads[50]; in that of the ant-lion (_Myrmeleon_) the two ganglions of the trunk are separated by an interval from those of the abdomen, which are so contiguous as to resemble the rattle of the rattle-snake[51]. In others the internodes are longer, and the ganglions occur at nearly equal intervals, as in the larva of the _Ephemeræ_[52]; but in the majority they are unequal in length: thus in the scorpion the three first ganglions are the most distant[53]; in the hive-bee the third and fourth[54]; and in the spider the last[55].

2. The ganglions also in different species, and often in the same insect in its different states, vary in their _number_. Thus in the grub of the rhinoceros-beetle the whole spinal marrow appears like a _single_ ganglion divided only by transverse furrows[56]; in the water-scorpion there are _two_[57]; in the louse there are _three_[58]; in the rhinoceros-beetle there are _four_[59]; _five_ in the stag-beetle[60]; _seven_ in the hive-bee and some _Lepidoptera_[61]; _eight_ in the grub of the stag-beetle[62]; _nine_ in the great _Hydrophilus_[63]; _ten_ in _Dytiscus_[64]; _eleven_ in the grub of the great _Hydrophilus_[65]; _twelve_ in the grub of _Dytiscus_ and the caterpillars of _Lepidoptera_[66]; _thirteen_ in the larva of _Æshna_[67]; and _twenty-four_ in _Scolopendra morsitans_[68]. You must observe that, generally speaking, the number of ganglions is less in the _imago_ than in the _larva_. With regard to the distribution of these knots to the different primary parts of the body, the following table will exhibit it, as far as I am acquainted with it, at one view. I omit those in which the ganglions are only in _one_ of these parts.

Head. Trunk. Abdomen.

_Acrida viridissima_ 1 3 6[69]

_Hydrophilus piceus_ 1 6 2

_Clubiona atrox_ 0 2 1

_Gryllotalpa vulgaris_ 0 2 7[70]

_Myrmeleon, Larva_ 0 2 8[71]

_Eristalis tenax_ 0 3 2[72]

_Apis mellifica_ 0 3 4

_Ephemera, Larva_ 0 3 7

_Æshna, Larva_ 0 6 7

3. I am next to say a few words upon the _shape_ of the ganglions. Most commonly it approaches to a _spherical_ figure, but in many instances, as I said before, they, as well as the brain, consist of _two_ lobes: they are, however, seldom all precisely of the same shape. In the _Dytisci_, and _Carabi_, the last is marked with a transverse furrow, which seems to indicate the reunion of two[73]; in the stag-beetle, the first ganglion is oval or elliptical, the second hexagonal; the third and fourth shaped like a crescent, and the last like an olive[74]; in the caterpillar of the great goat-moth the first is oblong and constricted in the middle, and the seven last are rhomboidal[75]; in the great _Hydrophilus_ the _second_, and in the silk-worm _all_ the ganglions are quadrangular[76]; in _Hypogymna dispar_ the _third_ is heart-shaped[77]; the great ganglion which forms the spinal marrow of the cheese-maggot is pear-shaped[78]; that of the grub of the rhinoceros-beetle is fusiform[79]; and in the scorpion all the ganglions are lenticular[80]. But the most remarkable in this respect are those of a spider (_Clubiona atrox_): in this insect the brain sits upon a bilobed ganglion of the ordinary form, which is immediately followed without any internode by another bilobed one, terminating on each side in four pear-shaped processes or fingers, which give it a very singular appearance[81].

iii. The _nerves_[82] of insects, as of other animals, are white filaments running from the brain and spinal marrow to every part of the body which they are destined to animate; and their numerous ramifications, when delineated, form no unpleasing picture[83]. In the caterpillar of the goat-moth the accurate Lyonet counted _forty-five_ pairs of them, and _two_ single ones, making in all _ninety-two_ nerves; whereas in the _human_ body anatomists count only _seventy-eight_[84]. From the brain issue several pairs, which go to the _eyes_, _antennæ_, _palpi_, and other parts of the mouth: sometimes those that render to the mandibles issue from the first ganglion, as in the larva of _Dytiscus marginalis_, the stag-beetle, &c.[85]; those both of _mandibles_ and _palpi_ in the great _Hydrophilus_[86]; and in _Blatta_ some which act also upon the _antennæ_[87].

The _optic_ are usually the most conspicuous and remarkable of the nerves. In some insects with large eyes, as many _Neuroptera_, _Hymenoptera_, and _Diptera_, their size is considerable; in the hive-bee they present the appearance of a pair of kidney-shaped lobes, larger than the brain[88]; in the dragon-flies, whose brain consists of two very minute lobes, these nerves dilate into two large plates of a similar shape, which line all the inner surface of the eyes[89]; in the stag-beetle they are pear-shaped, and terminate in a bulb, from which issue an infinity of minute nerves[90]; it is probable that this takes place in all cases, and that a separate nerve renders to every separate lens in a compound eye[91]; the optic nerve in _Dytiscus_ and _Carabus_ is pyramidal, with the base of the pyramid at the eye and the summit at the brain[92]; in _Eristalis tenax_ it is very large, cylindrical, and of a diameter equal to the length of the last-mentioned part, upon the side of which it is supported; it terminates in a very large bulb corresponding to the eye[93]: in _Scolopendra morsitans_ the optic nerves divide into four branches long before they arrive at the eyes, and in this insect the nerves which render to the antennæ are so thick as to appear portions of the brain, which they equal in diameter[94]. Swammerdam discovered in the grub of the rhinoceros-beetle and in the caterpillar of the silk-worm, a pair of nerves which he regarded as analogous to the _recurrent nerves_ in the human subject, and therefore he distinguishes them by the same name[95]: they issue from the lower surface of the brain, or that which rests on the _œsophagus_, and at first go towards the mouth, but afterwards turn back, and uniting form a small ganglion; this produces a single nerve, which passing below the brain follows the œsophagus to the stomach, where it swells into another ganglion, from which issue some small nerves that render to the stomach, and one more considerable which accompanies the intestinal canal, producing at intervals lateral filaments which lose themselves in the tunics of that tube[96]. Lyonet afterwards discovered these nerves in the caterpillar of the goat-moth[97], and Cuvier in other insects[98].