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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 _oesophagus_ 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 aerial
vessels, which are not discoverable in the latter[