[Illustration: _Printed by H. Howard, RA._
_Engraved by W. T. Fry._
_William Kirby. M.A. F.R. L.S. &c_
_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.
VOL. III.
_LONDON:_
PRINTED FOR
LONGMAN, REES, ORME, BROWN, AND GREEN,
PATERNOSTER ROW.
1826.
PRINTED BY RICHARD TAYLOR,
SHOE LANE, LONDON.
ADVERTISEMENT.
The publication of the concluding volumes of the "Introduction
to Entomology" has been unavoidably delayed by the continued ill
health of one of the Authors, which has devolved upon the other a
considerable increase of labour, and demanded a greater expenditure
of time than would otherwise have been required: for though Mr.
SPENCE put every facility in Mr. KIRBY'S power, and had drawn up a
rough copy of every Letter belonging to his department; yet, as most
of them had been written several years ago, many curious facts, and
a great variety of interesting information subsequently derived from
various sources, were necessarily to be inserted, and the whole to be
prepared for the press.
When the thousands of objects that were to be examined, and many of
them repeatedly, in composing the Letters on the External Anatomy
of Insects, are considered, it will not appear surprising if some
errors should have crept in; especially as Mr. KIRBY was deprived of
the effectual help formerly derived from the acumen, learning, and
judgement of his esteemed coadjutor, by his lamented and protracted
indisposition: but it is hoped that these errors will be found of
minor importance, and not to affect any general principles advanced.
The same remarks are also in part applicable to the Anatomical and
Orismological Tables (VOL. III. p. 354-393, and VOL. IV. p. 257-354),
which were drawn up by the Authors jointly many years ago, before any
other portion of the work was composed, but which have, especially
the former, required considerable alterations and additions in
consequence of subsequent observations and information.
It will not be amiss here to state, in order to obviate any charge
of inconsistency in the possible event of Mr. KIRBY'S adverting in
any other work to this subject, that though on every material point
the authors have agreed in opinion, their views of the _theory of
instinct_ do not precisely accord. That given in the second and
fourth volumes is from the pen of Mr. SPENCE.
It was originally intended, as mentioned in the Preface, to have given
a complete list of Entomological works, of which a large portion was
drawn up; but the great length to which more important matters have
extended, has rendered necessary the intire omission of this list,--an
omission in some degree compensated by the catalogue of _Authors
quoted_, which comprises most of the standard Entomological works.
ERRATA.
Page. Line.
29 27, _for_ Pseudo-c_o_rdia _read_ Pseudo-c_a_rdia.
33 7, _for_ 1/12 _read_ 1-1/2.
35 7 and elsewhere, _for_ Gigas _read_ grandis.
46 16, _for_ number and situation _read_ in some respects.
98 6, _for_ Furtina _read_ Jurtina.
121 note^d, _for c read c´._
135 note^b, _for_ XXIV. _read_ XXIII.
137 note^a, _for_ 17 _read_ 18.
251 4, _for_ ten _read_ nine.
378 10, } _for_ frœnum _read_ frænum.
359 21, }
422 note^b, _for_ a´ _read_ a´´.
425 note^b, _for_ b´´ _read_ b´.
471 1, _dele_ Pelecotoma.
10, _for_ orbicular _read_ subtriangular.
512 antepenult. _After_ genera _insert_ except in some _Acridæ_, as
_A. viridissima_.
562 note^c, _for_ πνεω _read_ πνυμι.
606 5, _for_ Heteropterous _read_ Homopterous.
DIRECTIONS TO THE BINDER.
The Synoptical Table of the Nomenclature of the Parts of the External
Crust of Insects should be placed opposite to page 354.
Plates VI-XX. should be placed in this Volume, and the remainder in
the Fourth.
It is however suggested to Purchasers, that in binding complete Sets
of the Work, a separate Volume may be formed of the Synoptical Table,
the Plates and their Explanations, and the Indexes.
CONTENTS OF VOL. III.
Letter. Page.
XXVIII. Definition of the Term _Insect_ 1-51
XXIX. States of Insects. _Egg state_ 52-104
XXX. The same Subject continued. _Larva
state_ 105-237
XXXI. The same Subject continued. _Pupa
state_ 238-290
XXXII. The same Subject continued. _Imago
state_ 291-347
XXXIII. External Anatomy of Insects. _Terms
and their Definition_ 348-393
XXXIV. The same Subject continued. _The Head
and its Parts_ 394-528
XXXV. The same Subject continued. _The
Trunk and its Parts and Organs_ 529-697
XXXVI. The same Subject continued. _The Abdomen
and its Parts_ 698-720
NOTICE RESPECTING VOL. I. AND II.
It being judged expedient, since the publication of the last Edition
of the first and second Volumes of this Work, to adopt a new plan
with respect to the reference letters of the Plates, the Reader is
requested to make the following corrections in those Volumes.
VOL. I.
Page. Note.
125 ^e, _for_ f, d _read_ a´´.
273 ^a, _for_ a _read_ _a_.
395 ^a, _for_ 29, 30 _read_ 13.
VOL. II.
244 ^c, _for_ a _read_ _a_.
319 ^b, _for_ 10 _read_ 14.
348 ^a, _for a read e´´´._
353 ^a, _for_ 7--. _read_ 16--.
366 ^b, _for a read s´´, v´´´._
^c, _for b read t´´._
405 ^a, _for_ 1.8. aa _read_ 18. _c_†.
^b, _for_ bb _read_ _q´´´_.
406 ^e, _for_ bb _read_ _C´´_.
407 ^e, _for_ cc _read_ _C´´ C´´_, which represent the bundles of
muscles in connexion with the drums. In the above
figure the mirror is the part directly under those
bundles.
AN
INTRODUCTION
TO
ENTOMOLOGY.
LETTER XXVIII.
_DEFINITION OF THE TERM_ INSECT.
What is an insect? This may seem a strange question after such
copious details as have been given in my former Letters of their
history and economy, in which it appears to have been taken for
granted that you can _answer_ this question. Yet in the scientific
road which you are now about to enter, to be able to define these
creatures technically is an important first step which calls for
attention. You know already that a butterfly is an insect--that
a fly, a beetle, a grasshopper, a bug, a bee, a louse, and flea,
are insects--that a spider also and centipede go under that name;
and this knowledge, which every child likewise possesses, was
sufficient for comprehending the subjects upon which I have hitherto
written. But now that we are about to take a nearer view of them--to
investigate their anatomical and physiological characters more
closely--these vague and popular ideas are insufficient. In common
language, not only the tribes above mentioned, but most _small_
animals--as worms, slugs, leeches, and many similar creatures, are
known by the name of _insects_. Such latitude, however, cannot be
admitted in a scientific view of the subject, in which the class
of insects is distinguished from these animals just as strictly as
beasts from birds, and birds from reptiles and amphibia, and these
again from fishes. Not, indeed, that the just limits of the class
have always been clearly understood and marked out. Even when our
correspondence first commenced, animals were regarded as belonging
to it, which since their internal organization has been more fully
explained, are properly separated from it. But it is now agreed on
all hands, that an earthworm, a leech, or a slug, is not an insect;
and a Naturalist seems almost as much inclined to smile at those who
confound them, as Captain Cook at the islanders who confessed their
entire ignorance of the nature of cows and horses, but gave him to
understand that they knew his sheep and goats to be birds.
You will better comprehend the subsequent definition of the
term _Insect_, after attending to a slight sketch of the chief
classifications of the animal kingdom, more especially of the
creatures in question, that have been proposed. That of Aristotle
stands first. He divides animals into two grand sections,
corresponding with the _Vertebrata_ and _Invertebrata_ of modern
Zoologists: those, namely, that have blood, and those that have it
not[1]:--by this it appears that he only regarded _red_ blood as
real blood; and probably did not suspect that there was a true
circulation in his _Mollusca_ and other white-blooded animals. His
_Enaima_, or animals that have blood, he divides into _Quadrupeds_,
_Birds_, _Fishes_, _Cetacea_, and _Apods_ or reptiles; though
he includes the latter, where they have four legs, amongst the
quadrupeds[2]; and his _Anaima_, or animals without blood, into
_Malachia_, _Malacostraca_, _Ostracoderma_, and _Entoma_. The
first of these, the _Malachia_, he defines as animals that are
externally fleshy and internally solid, like the _Enaima_; and
he gives the _Sepia_ as the type of this class, which answers to
the _Cephalopoda_ of the moderns. The next, the _Malacostraca_,
synonymous with the _Crustacea_ of Cuvier and Lamarck, are those,
he says, which have their solid part without and the fleshy within,
and whose shell will not break, but splits, upon collision[3]. The
_Ostracoderma_, corresponding with the _Testacea_ of Linné, he also
defines as having their fleshy substance within, and the solid
without; but whose shell, as to its fracture, reverses the character
of the _Malacostraca_. He defines his last class _Entoma_, in Latin
_Insecta_, with which we are principally concerned, as animals whose
body is distinguished by _incisures_, either on its upper or under
side, or on both, and has no solid or fleshy substance separate, but
something intermediate, their body being equally hard both within and
without[4]. This definition would include the _Annelida_ and most
other _Vermes_ of Linné, except the _Testacea_, which accordingly
were considered as insects by those Zoologists that intervened
between Aristotle and the latter author. The Stagyrite, however, in
another place, has expressly excluded all _apods_[5]. From other
passages in his works, it appears that he regarded the _Vermes_, &c.
either as _larvæ_, or as produced spontaneously and not _ex ovo_[6].
This definition of an insect, though partly founded on misconception,
as well as his primary division of animals in general, is by no means
contemptible. If you look at a bee or a fly, you will observe at first
sight that its body is _insected_, being divided as it were into three
principal pieces--head, trunk, and abdomen[7]; and if you examine
it more narrowly, you will find that the two last of these parts,
especially the abdomen, are further subdivided. And this character
of _insection_, or division into segments, more or less present in
almost every insect[8], is not to be found (with the exception of the
_Crustacea_, which Aristotle distinguishes by the nature of their
integument and its contents) in any of the other classes into which he
divided animals without blood. It was on account of this most obvious
of their characters, that these little creatures were in Greek named
_Entoma_, and in Latin _Insecta_; and from the former word, as you
know, our favourite science takes the name of _Entomology_.
Pliny adhering to the definition of Aristotle, as far as it relates
to the _insection_ of the animals we are speaking of, expressly
includes _Apods_, as well as _Aptera_, amongst them[9]; and in
this was followed, without any attempt at improvement, by all the
entomological writers that intervened between him and the great
Aristotle of the moderns, Linné.
This illustrious naturalist, aware of the incorrectness of the
primary divisions of the animal kingdom founded upon the presence or
absence of blood, establishes his system upon the structure of the
heart, and upon the temperature and colour of the circulating fluid.
He divided animals into two great _sections_ or _sub-kingdoms_, each
comprising two _classes_. His _first_ section included those having
a heart with _two_ ventricles, _two_ auricles, and _warm_ and red
blood, viz. the _Mammalia_ or beasts, and the _Aves_ or birds. His
_second_, those having a heart with _one_ ventricle, _one_ auricle,
and _cold_ and red blood, namely, the classes _Amphibia_, which
included reptiles, serpents, &c. and _Pisces_ or fish. His _third_,
those having a heart with _one_ ventricle and _no_ auricle, and _cold
white_ sanies in the place of blood, namely, his classes _Insecta_ et
_Vermes_, including the _Invertebrate_ animals of Lamarck. Thus the
first of Aristotle's great divisions he increased by the addition of
a new and very distinct class, the _Amphibia_, by which some ground
was gained in the science; but as much was lost by his compressing
the four classes of which the last consisted into two, by which
the natural classes of _Cephalopoda_ and _Crustacea_ merged under
_Insecta_ and _Vermes_. Linné was not aware of the extraordinary
fact, that the _Cephalopoda_ have three hearts; and that though the
_Crustacea_ and _Arachnida_ have a circulation, _Insects_ have none,
or he would never have taken this retrograde step.
Indeed Linné's definition of an _Insect_ is, in many most material
points, inapplicable, not only to the _Crustacea_, but to many other
animals included under that denomination. This will appear evident
from a very slight examination. Thus it runs: "_Polypod animalcula,
breathing by lateral spiracles, armed every where with an osseous
skin, whose head is furnished with movable sensitive antennæ_[10]."
Now of this definition only the first member can be applied to the
whole class which it is meant to designate; for the entire genus
_Cancer_ L., which, with some others, forms the class _Crustacea_ of
the moderns, does not respire by _spiracles_ at all, but by _gills_;
and the same in some degree may be said of spiders, scorpions, &c.
With the last member of the definition Linné himself must have been
aware that a large number of what he conceived to be insects were at
variance, as mites, spiders, and many other of his apterous tribes:
though from some very recent observations of M. Latreille[11],
there seems some ground for thinking, that in these the antennæ
are represented by the mandibles, palpi, &c.[12], and to the soft
flexible, coriaceous or membranous skin of a vast number of insects,
the term _cutis ossea_ is by no means applicable.
Evident as these incongruities are, when the Herculean task which
Linné imposed upon himself, and the vastness and variety of his
labours, are considered, they become very venial. Indeed, unless he
had divided his class _Insecta_ into two or more, it was impossible
to define it intelligibly to ordinary readers, otherwise than nearly
in the terms which he actually employed; and these characters,
restricted and amended by qualifying clauses, are still those to
which recurrence must be had in a popular definition of the class,
when separated as it ought to be from the _Crustacea_ and _Arachnida_.
Pennant, Brisson, and other zoologists, who, attending to _nature_
rather than _system_, saw the impropriety of uniting a crab or a
lobster in the same class with a bee or a beetle, long since assigned
the _Crustacea_ their ancient distinct rank. "But these changes,"
as Latreille observes[13], "being only founded upon _external_
characters, might be deemed arbitrary; and to fix our opinion, it was
necessary to have recourse to a decisive authority--the _internal_
and comparative organization of these animals." It results from the
observations of the most profound comparative anatomist of our age,
M. Cuvier, that the _Crustacea_ and _Arachnida_ differ from insects
properly so called, and particularly from those that are furnished
with wings, in having a complete system of circulation, a different
mode of respiration, and that they have a more perfect organization.
Influenced by these motives, both Cuvier and Lamarck have considered
them as forming two classes separate from insects. Treviranus, led by
considerations founded on the organs of circulation, of respiration,
and of generation, is of opinion that spiders and scorpions ought
to form one class with the _Crustacea_: he observes, however, that
the nervous system of all three is very dissimilar; and that in an
arrangement founded on this circumstance, the organs of motion, and
the external shape, even spiders and scorpions must be placed in
different classes[14].
It is to be observed with regard to the _Arachnida_ of the French
school, that the class as laid down by them includes several
animals that have no circulation, and breathe by _tracheæ_, of
which description are the mites (_Acarus_ L.), and the harvest-men
(_Phalangium_ L.) &c.; and therefore it has been divided into two
orders, _Pulmonaria_ and _Tracheana_; but if the definition from
the internal organization be adhered to, the latter should either
remain with the class _Insecta_, or form a new one by themselves. Yet
the animals that compose the _Trachean_ order of _Arachnida_, their
external form considered, are certainly much more nearly related to
the spiders and scorpions than to any members of the class _Insecta_
at present known. This circumstance, perhaps, may seem to throw some
doubt upon the modern system of classification.
I must further observe, that the assertion of Treviranus, which appears
to intimate that the respiration of the _pulmonary Arachnida_ is the
same with that of the _Crustacea_, is not quite correct, since in
the latter the _branchiæ_ or gills are _external_, and in the former
_internal_, the air entering by spiracles before it acts upon them[15].
It may not be amiss in this place to lay before you the principal
points in which the _Crustacea_ and _Arachnida_ agree with _Insecta_,
and also those in which they differ.
The _Crustacea_ agree with _Insecta_ in having a body divided into
segments, furnished with jointed legs, compound eyes, and antennæ.
Their nervous system also is not materially different, and they
are both oviparous. They differ from them in having the greater
insections of the body less strongly marked; in the greater number
of legs on the trunk, the anterior ones performing the office of
maxillæ: in their eyes usually on a moveable footstalk: their
palpigerous mandibles; and their four antennæ at least in the great
majority. But the principal difference consists in the internal
organization and the fountains of vitality; for the _Crustacea_ have
a double circulation, the fountain of which is a heart in the middle
of their thorax[16]. They have too a kind of gizzard and liver,
at least the _Decapods_[17], and their respiration is by gills.
Genuine insects terminate their existence after they have laid their
eggs[18]; but the _Crustacea_ live longer, and lay more than once.
The _Arachnida_ will be found to differ from insects more widely than
even the _Crustacea_. They agree in their jointed legs and palpi;
immoveable eyes; and in being covered with a coriaceous or corneous
integument: but they differ in having a system of circulation;
gills instead of tracheæ; their organs of generation double; and
the females lay more than once in their lives. Their head also is
not distinct from the trunk as in insects; they have no compound
eyes; and their antennæ, if we admit the opinion on this head of MM.
Latreille and Treviranus, that they have representatives of these
organs, differ totally in structure, situation, and use, from those
of the great body of insects. In the _Araneidæ_ or Spiders, their
body seems to have no segments or incisure but that which separates
the abdomen from the trunk; and in the _Scorpionidæ_ they are
observable only in the abdomen. Other particulars might be enumerated
in which these two classes differ from insects; but these will be
sufficient to convince you that Aristotle and MM. Cuvier and Lamarck
were justified in separating them.
The two last-mentioned authors made further improvements in Zoology.
The latter, from the consideration of the general structure of animals,
perceiving that Aristotle's _Enaima_ were distinguished from his
_Anaima_, by being built as it were upon a vertebral column, very
judiciously changed the denomination, which was indeed improper, of
"_The Philosopher's_" two sub-kingdoms, into that of _Vertebrata_
or animals that have a vertebral column, and _Invertebrata_ or those
that have no vertebral column. These he distributes into three primary
divisions according to their supposed degrees of _intelligence_--Thus:
* _Apathetic Animals._ 1. INFUSORIA.
2. POLYPI.
3. RADIATA.
4. VERMES.
** _Sensitive Animals._ (_Epizoaria._)
5. INSECTA.
6. ARACHNIDA.
7. CRUSTACEA.
8. ANNELIDA.
9. CIRRHIPEDA.
10. MOLLUSCA.
*** _Intelligent Animals._ 11. PISCES.
12. REPTILIA.
13. AVES.
14. MAMMALIA.[19]
Profiting by the light afforded by the Aristotelian system, this
eminent zoologist improved, we see, upon that of Linné, by resolving
his _Insecta_ into three classes, and his _Vermes_ into seven,
interposing the Linnean _Insecta_ between the four first and three
last, in which he was not so happy, since as to _sense_ insects should
certainly occupy the place he has here assigned to the _Mollusca_.
In the work from which I have taken this statement of Lamarck's
system, that acute writer has given a sketch of another method of
arrangement, in which he has made the first deviation from the beaten
track of an unbroken and unbranching series. In the Supplement to
the first volume, he has distributed the _Invertebrata_ in a double
subramose series--one consisting of _articulate_, and the other of
_inarticulate_ animals[20].
Upon Lamarck's system, most of the modern ones, with some variation,
are founded. There is one, however, by a learned countryman of ours,
that is more unique, _sui generis_, and I may add profound, than any
that has yet appeared. I am speaking of that, you will perceive, of
which our friend Mr. Wm. MacLeay has given a detailed statement in
his _Horæ Entomologicæ_. In this he goes even far beyond what Lamarck
has attempted in the above sketch, and substantiates his claim to be
considered as one of those original thinkers, _rari nantes in gurgite
vasto_, that do not appear every day. The following are the principal
bases of his system.
1. That all natural groups, whether kingdoms or any subdivision of
them, return into themselves; a distribution which he expresses by
circles.
2. That each of these circles is formed precisely of _five_ groups,
each of which is resolvable into five other smaller groups, and so on
till you reach the extreme term of such division.
3. That proximate circles or larger groups are connected by the
intervention of lesser groups, which he denominates _osculant_.
4. That there are relations of analogy between the corresponding
points of contiguous circles.
This system he has represented by tables of circles inscribed with
the five primary divisions of each group. His first table exhibits a
general view of organized matter as distributed in the animal and
vegetable kingdoms--Thus:
[Illustration]
Our learned author here divides the animal kingdom into what may be
denominated five sub-kingdoms or provinces, in three of which (with
the exception of the _Crustacea_ and _Arachnida_ belonging to his
_Annulosa_) no circulation of blood is visible, but which obtains in
the rest. These he names--
1. ACRITA, consisting of the _Infusory Animals_, the _Polypi_, the
_Corallines_, the _Tæniæ_, and the least organized of the _Intestinal
Worms_.
2. RADIATA, including the _Jelly-fish_, _Star-fish_, _Echini_, and
some others.
3. ANNULOSA, consisting of _Insecta_, _Arachnida_, and _Crustacea_.
4. VERTEBRATA, consisting of _Beasts_, _Birds_, _Reptiles_,
_Amphibia_, and _Fishes_.
5. MOLLUSCA, including the numerous tribes of _shell-fish_,
_land-shells_, _slugs_, &c., which, from their mucous or gelatinous
substance, from their nervous system and the imperfection of their
senses, return again to the _Acrita_, though connected with the
_Vertebrata_ by having a heart and circulation.
His next set of circles shows the sub-division of these five
sub-kingdoms into classes--Thus:
[Illustration]
In this scheme the _osculant_ classes are those placed between the
circles. In the _Mollusca_ circle two classes are still wanting
to complete the quinary arrangement of that sub-kingdom. I am not
sufficiently conversant with the details of the animal kingdom
at large to hazard any decided opinion upon Mr. MacLeay's whole
system, or to ascertain whether all these classes are sufficiently
distinct[21]. My sentiments with regard to those of the _Annulosa_ I
shall state to you hereafter.
Upon a future occasion I shall consider more at large the station
to which insects seem entitled in a system of invertebrate animals,
which will not accord exactly with that assigned by MM. Cuvier and
Lamarck. But I am now in a field in which I have no intention to
expatiate further, than as it is connected with the subject of the
present letter. I shall therefore confine myself in what I have
more to say to the definitions of _Insecta_ that have been given by
modern authors, beginning with that of the zoologist last mentioned.
Insects form a part of his _second_ group, which he terms _sensitive_
animals (_animaux sensibles_), which group he thus defines: "_They
are sentient, but obtain from their sensations only perceptions of
objects--a kind of simple ideas which they cannot combine to obtain
complex ones._ Charact. _No vertebral column; a brain, and most
commonly an elongated medullary mass; some distinct senses; the
organs of movement attached under the skin: form symmetrical, by
parts, in pairs_[22]." This division of animals, from the kind and
degree of sense and intelligence that they possess, seems rather
fanciful than founded in nature, since many insects show a greater
portion of them than many vertebrate animals. Compare in this
respect a _bee_ with a _tortoise_[23]. Lamarck divides his group
of _animaux sensibles_ into two sections, namely, _Articulated_
animals, exhibiting segments or articulations in all or some of their
parts; and _Inarticulatcd_ animals, exhibiting neither segments
nor articulations in any of their parts. _Insecta_, _Arachnida_,
and _Crustacea_, belong to the first of these sections, which he
defines as "_those whose body is divided into segments, and which are
furnished with jointed legs bent at the articulations_[24]." INSECTA
he defines--"_Articulate animals, undergoing various metamorphoses,
or acquiring new kinds of parts--having, in their perfect state,
six feet, two antennæ, two compound eyes, and a corneous skin. The
majority acquiring wings. Respiration by spiracles_ (stigmates), _and
two vascular opposite chords, divided by plexus, and constituting
aeriferous tracheæ, which extend every where. A small brain at the
anterior extremity of a longitudinal knotty marrow, with nerves. No
system of circulation, no conglomerate glands. Generation oviparous:
two distinct sexes. A single sexual union in the whole course of
life_[25]." ARACHNIDA he defines--"_Oviparous animals, having at
all times jointed legs, undergoing no metamorphosis, and never
acquiring new kinds of parts. Respiration tracheal or branchial: the
openings for the entrance of the air spiraculiform (stigmatiformes).
A heart and circulation beginning in many. The majority couple
often in the course of life_[26]." I shall next add his definition
of CRUSTACEA: "_Oviparous, articulated, apterous animals, with a
crustaceous integument more or less solid, having jointed legs; eyes
either pedunculate or sessile, and most commonly four antennæ, with a
maxilliferous mouth seldom rostriform; maxillæ in many pairs placed
one over the other; scarcely any under-lip; no spiraculiform openings
for respiration; five or seven pair of legs; a longitudinal knotty
marrow terminated anteriorly by a small brain. A heart and vessels
for circulation. Respiration branchial with external branchiæ,
sometimes hid under the sides of the shell of the thorax, or shut
in prominent parts; sometimes uncovered, and in general adhering to
particular legs or to the tail. Each sex usually double_[27]."
I have given Lamarck's definitions of these three classes, all
considered as _Insecta_ by Linné, that by comparing them together
you may be better enabled to appreciate the system of this author.
On looking over the characters of the _Arachnida_ as here given,
you will see at once that it consists of heterogeneous animals--for
in fact he includes in this class not only the _Trachean Arachnida_
of Latreille, but the _Ametabolia_ of Dr. Leach, or the _Hexapod_
Aptera, and the _Myriapoda_.
I shall next copy for you Latreille's latest definition of _Insecta_
and _Arachnida_.
"INSECTA: _A single dorsal vessel representing the heart: two
trunks of tracheæ running the whole length of the body, and opening
externally by numerous spiracles; two antennæ; very often upper
appendages for flight, indicating the metamorphosis to which the
animal is subject when young; legs most commonly reduced to
six._ ARACHNIDA: _Distinguished from_ Crustacea _by having their
respiratory organs always internal, opening on the sides of the
abdomen or thorax to receive the respirable fluid. Sometimes these
organs perform the office of lungs, and then the circulation takes
place by means of a dorsal vessel, which sends forth arterial, and
receives venose branches. Sometimes they are tracheæ or air-vessels,
which, as in the class_ Insecta, _replace those of circulation. These
have only the vestige of a heart, or a dorsal vessel alternately
contracting and sending forth no branch. The absence of antennæ,
the reunion of the head with the thorax, a simple trachea but
ramified and almost radiating, serve to distinguish these last_
Arachnida, _or the most imperfect of insects, which respire only by
tracheæ_[28]." Under this head he observes--"Of all these characters,
the most easy to seize and the most certain would doubtless be,
if there were no mistake in it, that of the absence of antennæ;
but later and comparative researches, confirmed by analogy, have
convinced me, that these organs, under particular modifications it
is true, and which have misled the attention of naturalists, do
exist[29]:" and he supposes, from the situation and direction of
the _mandibles_ of the _Arachnida_, corresponding with that of the
_intermediate_ pair of _antennæ_ in _Crustacea_, that they really
represent the latter organs. If this supposition be admitted, their
use is wholly changed; the palpi, in fact, executing the functions of
antennæ, which probably induced Treviranus to call them _Fühlhörner_
(_Feelinghorns_). Perhaps these last may be regarded as in some sort
representing the _external_ antennæ of the _Crustacea_? With regard
to _Insecta_, their antennæ seem to disappear in the _Pupiparæ_
Latr., or the genus _Hippobosca_ L.
The above definitions of the _Arachnida_ by these two celebrated
authors, appear to me the reverse of satisfactory. When we are told
of animals included in it, that some breathe by gills and others by
tracheæ, that some have a heart and circulation and others not, we
are immediately struck by the incongruity, and are led to suspect
that animals differing so widely in the fountains of life ought
not to be associated in the same class. A learned zoologist of our
own country, Dr. Leach, seems to have made a nearer approach to a
classification in accordance with the internal organization, by
excluding from _Arachnida_ the _Acari_ and _Myriapoda_.
Sub-kingdom ANNULATA Cuv.
* Gills for respiration. _Classes._
_Legs sixteen:_ Antennæ two or four 1 CRUSTACEA.
** Sacs for respiration.
_Legs twelve:_ Antennæ none 3 ARACHNÖIDEA.
*** Tracheæ for respiration.
a. No Antennæ.
4 ACARI.
b. Two Antennæ.
_Six thoracic legs:_ Abdomen also bearing legs 2 MYRIAPODA.
_Six thoracic legs:_ No abdominal legs 5 INSECTA[30].
Mr. MacLeay, on whose system I shall now say a few words, divides
his sub-kingdom _Annulosa_ into five classes, namely, _Crustacea_,
_Ametabola_, _Mandibulata_, _Haustellata_, _Arachnida_. From
the _Crustacea_ he goes by the genus _Porcellio_ Latr. to
_Iulus_[31], which begins his _Ametabola_: these he connects with
the _Mandibulata_, by _Nirmus_, which he thinks approaches some of
the corticarious _Coleoptera_[32]. This class he appears to leave
by the _Trichoptera_ Kirby, and so enters his _Haustellata_ by the
_Lepidoptera_[33], and leaves it again by the _Diptera_ by means of
the _Pupiparæ_ Latr., especially _Nycteribia_, connecting this class
with the _Arachnida_, which he enters by the Hexapod _Acari_ L.[34],
and these last he appears to leave by the _Araneidæ_, and to enter
the _Crustacea_ by the Decapods[35]: thus making good his circle
of classes, or a series of Annulose animals returning into itself.
Mr. MacLeay's whole system upon paper appears very harmonious and
consistent, and bears a most seducing aspect of verisimilitude; but
it has not yet been so thoroughly weighed, discussed, and sifted, as
to justify our adopting it _in toto_ at present: should it, however,
upon an impartial and thorough investigation, come forth from the
furnace as gold, and be found to correspond with the actual state
of things in nature, my objections, which rest only upon some parts
of his arrangement of _Annulosa_, would soon vanish. Some of those
objections I will state here, and some will come in better when I
treat of the Systems of Entomology. My first objection is, that his
_Ametabola_, _Mandibulata_, and _Haustellata_, approach much nearer
to each other than they do to the other two classes of his circle,
or than even these last to each other; so that under this view it
should primarily consist of _three_ greater groups, resolvable, it
may be, into five smaller ones. My next objection is, that he has
also considered the _Trachean_ and _Pulmonary_ Arachnida as forming
_one_ class. Whether an animal breathes by gills or tracheæ, or has
a circulation or not, is surely as strong a reason for considering
those so distinguished as belonging to different classes, as the
taking of their food by suction or by manducation is, for separating
others to the full as much or more nearly related as to their
external structure. But of this more hereafter. I cannot help, as a
last objection, lamenting that our learned author has rejected from
his system a term consecrated from the most remote antiquity, and
which, even admitting his arrangement, might have been substituted
for _Annulosa_, a name borrowed by Scaliger from Albertus Magnus,
neither of whom, in Entomology, is an authority to weigh against
Aristotle, from whom we derive the term _Insecta_, in Greek Εντομα.
As Fabricius did not alter Linné's _class_ Insecta, but merely broke
up his _orders_ into new ones, which he named classes, I shall give
you a detail of the alterations he introduced into the science in a
future letter.
Having stated what my predecessors have done in classification, I
shall next proceed to lay before you my own sentiments as to--_What
is an insect._ Since our correspondence commenced, the _Arachnida_,
principally on account of their internal organization, have been
excluded from bearing that name, carrying with them, as we have seen,
several tribes, which as yet have not been discovered to differ
materially in that respect from the present _Insecta_: for the sake,
therefore, of convenience and consistency, that I may, as far as the
case will admit, adhere to the Horatian maxim
---- Servetur ad imum
Qualis ab incepto processerit et sibi constet,
I shall regard as _Insects_ all those _Annulosa_ that respire by
tracheæ[36] and have no circulation, considering the _Trachean
Arachnida_ and the _Myriapoda_ for the present as sub-classes,
the one bordering upon the _Arachnida_, and the other upon the
_Crustacea_. Some of these I am ready to own seem separated by an
interval sufficiently wide from the _Hexapods_, which may be regarded
as more peculiarly entitled to the denomination of _Insects_. The
most striking differences will be found in the coalition of the head
with the trunk in some (_Phalangidæ_), and the disappearance of the
annulose form of the body in others (_Acarus_ L.), so that the legs
only are jointed[37]. Yet an approach to such structure may be traced
in some Hexapods; for instance, the coalition of the head and trunk in
_Melophagus_, Latr., and that of the trunk and abdomen in _Sminthurus_,
Latr.[38] The _Myriapoda_ exhibit other remarkable differences; though
their head and trunk are distinct, the former antenniferous, and their
body annulose, the abdomen as well as the trunk is furnished with
legs, sometimes amounting to hundreds; but even to this a tendency
has been observed in some Hexapods[39]. If you examine a specimen
of _Machilis polypoda_, an insect related to the common sugar-louse
(_Lepisma saccharina_), you will find that the abdomen is furnished
with a double series of elastic appendages, which, being instruments
of motion, may be regarded as representing legs. It is worthy of
notice, that the _Myriapoda_ when first disclosed from the egg have
never more than _six_ legs[40], and keep acquiring additional pairs
of them and additional segments to their abdomen as they change their
skins: and it is equally remarkable, that many Hexapods are subject to
a law in some degree the very reverse of this, having many abdominal
legs in their first state, and losing them all in their last. The
union of the head with the trunk in the _Trachean Arachnida_ has
been regarded as almost an unanswerable argument, in spite of their
different internal organization, for including them in the same class
with the _Pulmonary Arachnida_; but the case of _Galeodes_, which,
though furnished with gills, (as an eminent Russian Entomologist Dr. G.
Fischer is reported to have discovered,) implying also a circulation,
and evidently belonging to the last-mentioned class, has nevertheless
a distinct thorax consisting of more than one piece, to which are
affixed only six legs[41], proves that even this circumstance possesses
no weight when set against the organization. If it was a difference in
this respect, that proved the _Crustacea_ classically distinct from
_Insecta_--that likewise was the principal reason for the separation
also of the _Arachnida_--it seems to follow that it ought also to
furnish an argument equally cogent for considering the _Trachean
Arachnida_, as well as the _Myriapoda_, distinct from the _Pulmonary_.
Another difference between the tribes in question is that of their
_metamorphosis_; and this appears to have had great weight with
Lamarck, inducing him to include in his _Arachnida_, not only the
_Tracheans_ and _Myriapods_, but even the apterous _Hexapods_, except
_Pulex_, or the _Anoplura_ and _Thysanura_ of modern authors. But the
metamorphosis alone, unless supported by the internal organization,
will I think scarcely be deemed a sufficient reason for separating
from each other tribes agreeing in that respect, and placing them
with others with which they disagree. The metamorphosis in some
of the Hexapods (_Lepidoptera_) consists in the loss of legs, the
acquisition of wings, a great change in the oral organs and in the
general form; in others (some _Coleoptera_), in the acquisition only
of wings and a change of shape, the oral organs remaining much the
same; in others again (_Curculio_ L.), in the acquisition of six legs
and wings and a change of form; in the flea, in the acquisition of
six legs and a change of form only; in the _Orthoptera_, _Hemiptera_,
&c. in the mere acquisition of wings; in the _Libellulidæ_, in
the loss of the mask that covers the mouth and the acquisition of
wings; in the _Diptera_, in the acquisition of six legs, wings, a
change of the oral organs and of the form; in some of the _Octopods_
(_Acarus_ L.), in the acquisition of a pair of legs; and in others
(_Phalangium_ and _Aranea_ L.), solely in a modification of them as
to their proportions; in the _Myriapods_, the alteration that takes
place in this respect is considerable; a large number of pairs of
legs is acquired and many additional abdominal segments, and the
proportion which the abdomen bears to the whole insect is quite
altered. In all these cases there is a change more or less, either
partial or general, of the original shape or organs of the animal;
and with regard to their metamorphosis, there is a greater difference
between a young and adult _Iulus_ than between a young and adult
_grasshopper_ or _bug_: so that if the metamorphosis, _per se_, be
assumed as a principal regulator of the class, the grasshopper or bug
have as little claim to belong to it as the _Iulus_.
M. Lamarck lays considerable stress upon another character--That
_Insecta_ engender only once in the course of their lives, and
_Arachnida_ more than once. But this, if examined, will be found to
be confined chiefly to the _Pulmonary Arachnida_, the _Tracheans_
following the law of _Insecta_ in this respect[42].
You may perhaps object that the bringing of the Trachean _Arachnida_
and the _Myriapoda_ into the class _Insecta_ will render the
approximation of them to a natural arrangement more difficult,
since it will be impossible at the same time to connect the
_Myriapods_ with the _Crustacea_, and the _Trachean_ with the
genuine _Arachnida_. I admit the validity of your objection, but
by no arrangement of insects in a simple series can we attain this
object: the difficulty, however, may perhaps be obviated in this way.
The distribution of organized matter, to adopt Mr. Wm. MacLeay's
metaphor[43], begins in a dichotomy, constituting the animal and
vegetable branches of the great tree of nature, and from these two
great branches, by means of infinite ramifications, the whole system
is formed, and, what is remarkable, these branches unite again so
as to represent a series returning into itself, a discovery due to
the patient investigation and acumen of our learned friend just
mentioned. Now, in considering the _Aptera_ order, we find at first
setting out from the Hexapods, a dichotomy, where the _Anoplura_
Leach branch off on the one side, and the _Thysanura_ Latr. on the
other--the former, by means of the _Pediculidæ_, taking their food
by suction, particularly _Phthirus_ Leach, or the Morpion (in which
the segments of the trunk and abdomen become indistinct[44]) approach
the _Octopods_ by the hexapod _Acari_ L.--the latter by _Machilis
polypoda_ tending towards the _Myriapods_. In the Octopod branch a
further dichotomy takes place, from which you proceed on one side to
the _Araneidæ_ in the _Arachnida_, by _Phalangium_, &c.; and in the
other by _Chelifer_, &c. to _Scorpio_. Again, the _Myriapod_ branch
also divides, going by the _Iulidæ_ to one branch of the _Isopod
Crustacea_, and by the _Scolopendridæ_ to another.
But there is another view of this subject before alluded to, which
may be repeated here, and which seems to prove that the types of
form in one natural group or class are reproduced in another; this
appears to result from the following parallel series:
_Neuropterous_ _Aptera._ _Arachnida._ _Crustacea._
_Larvæ._
Psocus Hexapoda Galeodes Larunda.
Myrmeleon _Phalangium_ Aranea {Decapoda
{ brachyura.
Octopoda
Panorpa? _Chelifer_ Scorpio {Decapoda
{ macroura.
{ _Thalassina
{ Scorpio_
{ especially.
Ephemera Myriapoda ***** Isopoda.
No type representing the _Myriapoda_ has yet been discovered in the
_Arachnida_ class; but I have little doubt of its existence. You will
observe that the analogies between the larvæ of the _winged_ orders
and the _Aptera_ were first noticed by Mr. W. MacLeay[45]. It is
probable that these parallel series of representatives of each other
might be increased, as well as the numbers in the respective columns.
What I have said will, I trust, sufficiently justify me for making
at present no more material alterations in the classification I
long since proposed to you[46]; I shall, therefore, now proceed
to define the objects I consider as _Insecta_; but I shall first
observe--that as Latreille considers the _branchiopod Crustacea_
or _Entomostraca_ of Müller as entitled to the denomination of
_Crustaceo-Arachnida_[47]; so his _Trachean Arachnida_ might be
called _Arachnida-Insecta_, and his _Myriapoda_, _Crustaceo-Insecta_.
_Sub-kingdom_--ANNULOSA[48].
_Class_--INSECTA.
_First Definition--From their_ external _Organization_.
BODY--divided into Head--Trunk--Abdomen.
HEAD.--Principal seat of the organs of sensation.
_Organs of sight._ Immoveable eyes, simple or compound, varying
in number.
_Organs of hearing_ uncertain, probably connected with the
antennæ.
_Organ of taste._ Ligula or palate within the mouth, accompanied
by the _organs of manducation_--a pair of mandibles and maxillæ
and an upper and lower lip, or their representatives.
_Organs of touch._ Principally two jointed antennæ or their
representatives, and four jointed feelers--two maxillary and
two labial.
TRUNK. Principal seat of the organs of motion.
_Organs of walking, running, or jumping._ Six or eight jointed
thoracic legs, in pairs.
_Organs of flight._ Four wings or their representatives, mostly
with branching nervures containing air-vessels; found in the
majority of the class.
_Organs_ (_external_) _of respiration._ A double set of lateral
spiracles, some for expiration.
ABDOMEN. Principal seat of the organs of generation.
_Organs of motion._ In the _Myriapods_ many pairs of acquired
legs; in the _Thysanura_ elastic ventral or caudal appendages.
_Organs of respiration._ A double series of lateral spiracles for
inspiration in the majority; in some only a single series, and
in others only a single pair.
_Organs of generation_ those common to the _Vertebrata_, but
retractile within the body, attended usually by various anal
appendages, particularly a forceps in the males, and an
ovipositor in the females.
_Second Definition--From their_ internal _Organization_.
SENSATION.
_Nervous System._ A small brain usually subbilobed, crowning a
knotty double medullary chord; nerves proceeding from the brain
and other ganglions to all parts of the body.
CIRCULATION.
_Heart_ replaced by a simple alternately contracting dorsal vessel
or pseudocardia, without arteries or veins, but filled with a
white cold sanies.
RESPIRATION.
_Lungs_ replaced by tracheæ, which receive the air from the
spiracles, and distribute it by bronchiæ infinitely ramified. #/
DIGESTION.
_Liver and biliary vessels_ in most replaced by from 2 to + 150
floating hepatic filaments opening into the space between the two
skins of the intestinal canal below the pylorus.
GENERATION.
_Internal organs. Males_--Vasa deferentia, and vesiculæ seminales,
and the other ordinary organs. _Females_--Ovary usually
bipartite, with palmate lobes; genital organs single and mostly
anal; one sexual union impregnates the female for her life.
_Development_. In their passage to their adult state, after they
have left the egg, _insects_ undergo several simultaneous changes of
their integument or successive moults, and the majority assume three
distinct forms, with distinct organs, which appear as rudiments in
their second state, and are completely developed in their last.
* * * * *
In defining the _Arachnida_ I shall only mention those particulars in
which they differ from _Insectæ_ in their external anatomy.
_Class_--ARACHNIDA.
BODY.
HEAD and Trunk usually not separated by a suture.
_Eyes_. Two to eight, not lateral.
_Mandibles_ cheliform or unguiculate, representing the interior
pair of the antennæ of the _Crustacea_.
_Palpi_ pediform or cheliform.
_Trunk_. Legs eight or their representatives: tibiæ mostly
consisting of two joints.
ABDOMEN with from two to eight spiracles.
SENSATION.