_capitulum_, in those in which that organ terminates in a knob),
it being thicker and often longer than the succeeding ones. In the
Capricorn and Darkling beetles, indeed (_Cerambyx_ and _Tenebrio_ L.),
the third joint is the longest, but the scape is still the thickest;
and in the stag-beetles (_Lucanus_ L.), many of the weevil tribes
(_Curculio_ L.), and those of the bees (_Apis_ L.), except in the
males, it is as long nearly as the remainder of the antennæ, which
forms an angle with it. In shape it is generally somewhat curved and
subclavate, or increasing in size from the base to the summit; but
it is sometimes straight and filiform, at others oblong or square,
at others again triangular, in several instances three-sided: in one
(_Cetonia cruenta_ F. _Genuchus_ K.) it is, as it were, broken, the
upper part forming nearly a right angle with the lower; in _Cerocoma
Schæfferi_ it is foliaceous; and it is occasionally suborbicular: and
probably many other forms might be enumerated.

The _Pedicellus_[1537] is the _second_, and may be deemed the _least
conspicuous_ joint of the antennæ. Though more slender than the scape,
it is generally thicker than that which immediately follows it. In
broken antennæ it is the hinge or pivot on which the _clavola_ or upper
member turns: it is usually very short, campanulate or bell-shaped, or
obconical; but in a species of bug (_Tetyra_, from New Holland--_T.
pedicellata_ Kirb. MS.) it is nearly as long as all the rest of
the joints taken together. In those species of _Lycus_, a genus of
beetles related to the glow-worm, that have flattened antennæ (as _L.
reticulatus_, _fasciatus_, &c.), this joint is almost received into the
socket of the scape, so that their antennæ appear at first to have only
_ten_ joints, but in those which have those organs filiform (as _L.
minutus_, _Aurora_, &c.) it is more conspicuous.

The _Clavola_[1538], or remaining joints of the antennæ taken
together, constitutes the principal part of the organ, which,
especially at its extremity, exercises its functions of touch, or
any other sense. The principal variations, as to form and structure,
that occur in this part will be mentioned in another place. I shall
only here observe, that in many instances the first joint of this
part is longer than the rest; but in _Tetyra pedicellata_ just
mentioned, it is by far the shortest, and shaped like the pedicel
of most insects. In the _Libellulina_, the Homopterous _Hemiptera_,
and those flies whose antennæ terminate in a bristle, the clavolet
is represented by the bristle. But in the flies which have a lateral
bristle, on the last joint, and those with triarticulate antennæ that
have no bristle, the terminal joint represents it. The clavolet often
terminates in a knob, or in several joints thicker than that which
precedes them. This varies greatly, not only in its form, but also
in the number of joints of which it is composed. Thus in _Paussus_,
_Platypus_, and many _Calandræ_, it consists of only a _single_
joint[1539]; in _Anthrenus_, _Ditoma_, &c. of _two_; in _Nitidula_,
_Geotrupes_, &c. of _three_[1540]; in _Tetratoma_, the _Silphidæ_,
of _four_[1541]; of _five_ in _Scaphidium_[1542]; of _six_ in
one species of _Languria_, of _seven_ in the common cockchafer
(_Melolontha vulgaris_[1543]); of _eight_ in _Diaperis Boleti_, in
which the whole clavolet forms the club[1544]; of _nine_ in _Oenas_;
and _ten_ in _Cerapterus_[1545]. All the above, you will observe,
are _beetles_. In the other orders there are _eleven_ joints in the
knob of some butterflies; _twelve_ in that of _Ascalaphus_[1546] and
_Myrmeleon_; and lastly, _fourteen_ in _Trachelus_[1547].

Under _structure_ also, the _number_ of joints of which antennæ in
general consist, should be considered. If you examine the insects
belonging to the different orders, you will find remarkable variations
in this respect. Let us run through them:--In the _Coleoptera_ the
natural number of joints is _eleven_; but this rule is not without
many exceptions. Thus, many have _fewer_ than the prescribed number:
_Paussus_ has only _two_[1548], _Claviger_ and _Platypus_ five,
_Dorcatoma_ and _Calandra_ eight[1549], _Geniates_ K. and _Phanæus_
MacLeay nine[1550], and lastly _Melolontha ten_[1551]. Others, again,
have _more_ than eleven joints: _Cebrio grandis_, _Chrysomela stolida_,
some _Saperdæ_, and several others, have _twelve_. In _Prionus
imbricornis_ the female has _nineteen_, and the male _twenty_[1552].
_Rhipicera marginata_ has _thirty-two_; and in a New Holland species
of this genus I counted _thirty-eight_. In the _Orthoptera_ I can
trace no general law in this respect. In _Locusta_ Leach in some
species you may count _fourteen_ joints, in others _sixteen_, and in
others _twenty-five_. In one, which appears to be a pupa, I found
only _thirteen_. In _Mantis_ they exceed _thirty_; but in _Blatta_,
from between _thirty_ and _forty_, they reach nearly _one hundred
and fifty_; often varying in number in different individuals of the
same species. The order _Hemiptera_ exhibits two peculiar types of
antennæ, which, with some exceptions, distinguish the two natural
sections into which M. Latreille has judiciously divided it. In the
_Heteropterous_ section they are _without_ a bristle at their end; and
in the _Homopterous_ one, with the exception of _Aphis_, _Thrips_,
&c. they _have_ one. In the genera of both these tribes, the number
of joints varies in these organs. Thus, exclusive of the seta, in
_Flata_ and _Cixius_ there are only _two_ joints; in _Galgulus_,
_Fulgora_, and _Cercopis_, there are _three_; in _Lygæus_, _Coreus_,
&c. there are _four_; in _Tetyra_, _Pentatoma_, _Tettigonia_, there
are _five_[1554]; in _Aleyrodes_ there are _six_; in _Aphis seven_; in
_Thrips eight_; in _Psylla ten_, the last of which is terminated by
two bristles[1555]; and in _Coccus eleven_. The _Neuroptera_ order,
as it stands at present, is regulated by no general rule with regard
to the number of joints in the antennæ of the insects that compose
it. Several types of form in these organs distinguish its discordant
tribes. The _first_ is that of the _Ephemeræ_, in which the antennæ
consist of two short joints, crowned by a short, tapering, _unjointed_
bristle. The _second_ is that of the _Libellulina_, similar to the
above, but with a _jointed_ bristle. The _third_ is that of _Psocus_,
in which the antenna has two short thick joints at the base, terminated
by a long filiform bristle, consisting of seven or eight joints, and
finer than a hair. Perhaps these three may be regarded as belonging to
a common type. The _fourth_ type is presented by the short filiform
antennæ of _Termes_; the _fifth_ by the setaceous ones of _Corydalis_,
_Hemerobius_, &c.; and the _sixth_ and last by the clavate and
capitate ones of _Myrmeleon_ and _Ascalaphus_. In the _Lepidoptera_
and _Trichoptera_ orders the antennæ, though varying in their general
form in the three tribes of which Linné formed his genera _Papilio_,
_Sphinx_, and _Phalæna_, with the exception of _Hepialus_, in which
the joints are few, are always _multiarticulate_:--we will therefore,
without further delay, proceed to the _Hymenoptera_. In Latreille's
tribe _Aculeata_ the general rule is, that the females shall have
_twelve_ joints and the males _thirteen_. In his _Ichneumonides_
the law seems to be, that the antennæ shall be multiarticulate
and setaceous; but in most of the other tribes of the order, even
those that in other respects are most nearly related,--as in his
_Tenthredinetæ_,--the number of joints of these organs varies without
end. Thus in _Hylotoma_ there are only _three_ joints[1556]; in _Cimbex
læta_[1557] _five_; in _C. axillaris_ and _Perga_ Leach[1558], six:
and so on to twenty-five or more[1559]. The same fluctuation in this
respect runs throughout the rest of the order. In the _Diptera_ there
are two general types of antennæ:--those of the _Tipulariæ_ Latr.,
consisting usually of from _fourteen_ to _sixteen_ joints, in the
males often resembling beautiful plumes; and those of the remainder of
the order, in which they do not exceed _three_ joints[1560]: though
the last, or _patella_, is often further divided into obsolete or
indistinct ones[1561]. These antennæ may be further subdivided into
_filatæ_ and _aristatæ_, or those without and those with a bristle,
either lateral or terminal.

The _clothing_ of antennæ also merits attention, since it is often
not a little remarkable. By clothing I understand the _down_ or
_hairs_ of every kind with which they are either generally or
partially covered. A great number of filiform and setaceous antennæ
of Predaceous beetles (_Cicindela_ L., _Carabus_ L.) have the first
two, three, or four joints naked, and the rest covered with a fine
down. In insects that have a knob at the end of these organs, whether
lamellated or perfoliate, this down is often confined to it, or to its
intermediate joints, and seems intermixed with nervous papillæ. These
are particularly visible in the flabellate antennæ of _Rhipicera_,
_Lampyris Latreillii_[1562], _Elater flabellicornis_[1563], &c.
covering both surfaces of the processes of the joints. In some male
bees these papillæ are inclosed in hexagonal spaces into which the
antennæ are marked out[1564]. It is to be observed, that in many
antennæ the joints of the clavolet have one or two bristles or more
at their apex, one above perhaps, and one below; the lower angle in
those of the serrated antennæ of _Elater_ is usually so furnished, and
sometimes the upper. In many Capricorn-beetles and various insects the
antennæ are clothed, instead of down, with stiffish hairs or short
bristles. Other insects have these organs, at least the clavolet,
beset with longer hairs standing out from them on all sides: of this
kind are those of a singular beetle (_Sarrotrium muticum_) sometimes
found in this country[1565]. Again, there are some that have only
their underside bearded with longer hairs; as _Lamia curculionoides_,
_speculifera_ K., and other Capricorns[1566]. In another of this tribe,
_Saperda hirsuticornis_, the three intermediate joints are ornamented
with branches of long black hairs, which give them an elegant and
feathery appearance[1567]. In _Callichroma alpina_ the apex of the
slate-coloured joints of its antennæ is bearded with black hairs. In
_Lamia reticulata_, and _Saperda fasciculata_ and _plumigera_, all
also Capricorns, a single bunch of hairs, resembling the brush of a
bottle-cleaner, signalizes the middle of the antenna[1568]: in _Saperda
scopulicornis_ K. this is star-shaped[1569]. Sometimes the _scape_ is
externally bearded, as in _Trox_, a beetle found in horns and bones;
and in many other Lamellicorns[1570]. In this last tribe the two
exterior leaves of the knob of the antennæ are often set with short
bristles[1571]; and in a minute beetle called by De Geer _Dermestes
atomarius_, the hairs of this part are said to form a brush[1572].

When insects, I mean more particularly _Coleoptera_, are about to
move from any station where they have been at rest, the first thing
they usually do, before they set a step, is to bring forward and
_expand_ their antennæ, which have either been carefully laid up
in a cavity fitted to receive them, or back upon the body: if they
terminate in a lamellated knob, they separate the lamellæ as far as
possible from each other; or if it is perfoliate, the joints of it
mutually recede. The object of this is evidently to collect notices
from the atmosphere, since the papillose part of these joints cannot
be applied to surfaces. When the animal begins to move, in many cases
the antennæ do the same, and continue their _motion_ till it stops
and returns to a state of repose. In the parasitic tribes of the
_Hymenoptera_ (_Ichneumon_ L.) they are kept in an almost constant
vibration. Many other insects move them in all directions without
any order or regularity; and others, when they elevate one depress
the other, and so proceed as if balancing themselves by means of
these organs like a rope-dancer. I have before stated to you how by
motions of their antennæ, ants and bees communicate their wants or
discoveries to each other, or make inquiry concerning any thing they
wish to know[1573]. But as I shall have occasion to make some further
remarks upon this subject, when the senses of insects are under
discussion, I shall for the present take my leave of it.

I shall conclude what I have to communicate to you relative to
the organs of which we are treating, with a few observations with
respect to their _station_ when the insect _reposes_. In the
Capricorn-beetles, _Eucera_ and other insects with _long_ antennæ,
they are merely turned back or on one side with no particular cavity
for their reception when unemployed, but probably the apex passes
under the body. In the Predaceous and Darkling beetles (_Carabus_
L., _Tenebrio_ L.) their station is usually under the sides of
the _prothorax_, and in the Tortoise beetles (_Cassida_), under
its anterior margin. In the Elastic beetles (_Elater_) they are
received into a groove between the under margin of that part and
the fore-breast (_antepectus_). In _Anthrenus_, when the animal
reposes or counterfeits death, the antennæ are concealed in a cavity
of the underside of the _prothorax_, at right angles with the
throat[1574]. In the kindred genus _Byrrhus_, another simulator of
death, a large cavity is excavated under the same part, to receive
both the forelegs and antennæ, a narrow space being left between
the angle of the _prothorax_ and fore-breast exactly admitting the
base of the latter, which are quite concealed under the former. In
_Cryptocephalus_ and _Chlamys_, kindred beetles, when at rest they
are withdrawn, except their scape and pedicel, with the head within
the cavity of the _prothorax_. In others they are turned under the
head, without any particular cavity for their reception; as in
many moths, _Apion_, &c. In most of the Lamellicorn beetles their
station is in the cavity formed by the eye and the throat, the knob
forming an angle with the rest of the antenna. In _Heterocerus_
they follow the contour of the eye[1575]. In _Brentus_, a genus
of weevils remarkably long and slender, they are turned back and
received by a slight longitudinal cavity of the rostrum; but in those
of this tribe (_Curculio_ L.) in which the clavolet forms an angle
with the long scape, this latter part, bending back, is laid up in
an oblique channel of that part; and the former, pointing in the
contrary direction, is folded upon it. In many flies (_Muscidæ_) a
vertical frontal cavity receives the antennæ, which point downwards
during repose[1576]. _Cryptocerus_, a very remarkable ant, has on
its head a singular square plate, the sides of which form a deep
longitudinal cavity: in this cavity the antennæ, quite concealed,
repose in safety. A cavity equally remarkable is exhibited by the
water-scorpions, particularly _Belostoma_, in which is a _very_ deep
kidney-shaped box, between the eye and throat, to receive and defend
its singular antennæ[1577]; which, when they are reposing, is closed
by the exterior harder joints, and from which it seems as if they
turned out, like a sentinel out of his box. In some aquatic genera
of beetles, as _Gyrinus_, _Parnus_, &c. they are withdrawn within
a lateral cavity of the same part, and are defended from the water
externally by the auricle at their base[1578]. The flabellated and
lamellated antennæ, previous to their being folded for repose, close
all their plates; which in action are as widely expanded as possible,
so as to form a knob; and in some the middle piece is entirely
concealed, as if in a box. In broken antennæ, or those in which the
clavolet forms an angle with the scape, the former is folded upon the
latter, with its point downwards.

II. _Subfacies._--Having dispatched the _Facies_, or _upper_ side of
the head, I am next to consider the _Subfacies_, or _under_ side:
but as the principal parts that occupy this side have been already
considered, I shall have no occasion to detain you long.

i. _Jugulum_[1579].--This part, which may be regarded as analogous to
the throat in vertebrate animals, lies between the cheeks; from which
it may usually be distinguished by being more lubricous and tumid, and
often separated by an impressed line. It is particularly conspicuous
and elevated in the Lamellicorn beetles, and calculated by its
lubricity for easy motion in the lower side of the cavity of the chest.
Its apex is the base in which the _mentum_ sits. It is not necessary to
enlarge further upon it, as it seldom exhibits striking characters.

III. _Collum_[1580].--In a large proportion of insects the head
inosculates in the trunk without the intervention of a neck, or
a constriction of the head behind. In the Orders _Orthoptera_,
_Trichoptera_, _Lepidoptera_, _Hymenoptera_, and _Diptera_, no
instance of it that I recollect occurs: in the _Coleoptera_ there
are many. In the Predaceous beetles, though several have no distinct
neck, yet others, as _Anthia_, &c. have a short and thick one;
and some few, as _Colliuris_, _Agra_, &c. one more pronounced.
Latreille has named a tribe in this Order _Trachelides_, from the
circumstance of their having a neck: in this tribe you will find the
blister-beetles (_Cantharis_ and _Mylabris_) both of the moderns and
the ancients. In the _Hemiptera_ order the water-scorpions _Nepa_,
&c. have a thick short neck; and _Zelus_, (a kind of bug,) one
longer and more slender; and, like _Raphidia_, the snake's-head fly,
which is similarly circumstanced, has the air of a serpent. Other
_Neuroptera_, likewise, have a neck; as _Hemerobius_, _Corydalis_,
&c. This part presents no other features that merit notice.

IV. _Myoglyphides_[1581].--The _Myoglyphides_, or muscle-notches, are
sinuses, some shallow and some deeper, in the posterior margin of the
upper side of the head, to which the levator muscles are affixed.
They seem principally confined to the _Coleoptera_; though, in some
cases at least, they may be traced in the Heteropterous _Hemiptera_.
These notches vary in number and depth in different insects. Thus
in _Buprestis_ there is only _one_ deep one[1582]: in _Copris_
there are _two_ shallow ones, in a deep sinus separated by a small
prominence[1583]: in _Elater_ and _Lamia_ there are also two not in a
sinus; and in _Calandra Palmarum_ there are four, two on each side,
with a prominent lobe between them[1584]. To each of these notches,
at its under margin, below the ligament that unites the occiput to
the trunk, a muscle to raise the head is usually attached.

FOOTNOTES:

[1151] See above, p. 86, 110, 243--.

[1152] Many species of _Hister_, _Curculio_ L., _Doryphora_ Illig.
are extremely hard, while _Cantharis_ Geoffr., _Meloe_ F., and
_Telephorus_ Geoffr., are very soft.

[1153] Thenard _Traité de Chimie Elémentaire_, iii. 637. n. 2005.
The other products he mentions are--a green oil, a yellow substance,
a black ditto, acetic acid, uric acid, phosphate of magnesia. The
vesicant matter consists of little micaceous laminæ soluble in
boiling alcohol and oil, but insoluble in water.

[1154] Coquebert _Illustr. Icon._ ii. _t._ xviii. _f._ 14, 15.

[1155] _Linn. Trans._ xii. _t._ xxii. _f._ 16.

[1156] This name I would give to _Locusta_ F., reserving, with Dr.
Leach, the latter name to the true _locust_ (_Gryllus_ F.). The name
_Conocephalus_, by which _Locusta_ F. has been distinguished, is
better restricted to those with a conical head.

[1157] PLATE XXVIII. FIG. 1, 2.

[1158] Huber _Nouv. Obs._ ii. 317.

[1159] VOL. I. p. 502--.

[1160] Hair, in the Holy Scriptures, is used as the symbol of
_strength_ or _power_. Judges xvi. 17--. 1 Cor. xi. 10.

[1161] _Anat. Compar._ ii. 624.

[1162] _Anat. Compar._ i. 119.

[1163] _Ibid._ ii. 540.

[1164] _Ibid._ 547.

[1165] _Ibid._ 553.

[1166] _Anat. Compar._ ii. 553.

[1167] _Ibid._ 557.

[1168] _Ibid._ 560.

[1169] PLATE XXVIII. FIG. 2. _a´´´._

[1170] _Anat. Compar._ ii. 557.

[1171] A _harmonic suture_ is when the margins of two flat bones
simply touch each other, without any intermediate substance; and a
_squamose_, when the thin margin of one covers that of the other.
_Anat. Compar._ i. 124. With regard to the flat portions of the
integument of insects, they have some motion; whereas a suture is an
articulation without movement. _Ibid._

[1172] Their connexion by means of a ligament classes them under
_Synneurosis_ (Monro _On the Bones_, Dr. Kirby's edit. 29), but even
this not strictly, since a common ligament connects them all. Those
of the trunk, as admitting a slight degree of motion, belong to
_Amphiarthrosis_ (_Anat. Compar._ i. 126), and those of the abdomen,
which are capable of larger movements, to _Diarthrosis_ (_Ibid._ 127).

[1173] See above, p. 309--.

[1174] In the _hornet_ and other wasps, this line on the inside of the
head furnishes a foundation for a septum, which in the sides of the
nose is very high, and connects also with the hind part of the head.

[1175] _Anat. Compar._ i. 445--.

[1176] _Ibid._ 447.

[1177] _Mém. sur les Anim. sans Vertèbr._ I. i, 11--. Comp. _Anat.
Compar._ iii. 314--.

[1178] It is probable that M. Cuvier took his idea of this first kind
of articulation, by contact of solid parts, from this individual
insect; since, besides its very prominent throat, there is on each
side of the _lower_ part of the occiput a small elevation, or
approach to a tubercle.

[1179] _Gen. des Crustac. et Ins._ ii. 246. _Regne Anim._ iii. 325.

[1180] This was written directly after the experiment recommended in
the text had been tried, with the result there stated.

[1181] Reaum. iv. 40. Latreille _Fourmis_, 328--.

[1182] PLATE VII. FIG. 2. k´´.

[1183] Clairville (_Ent. Helvet._ i. 44) appears to have been the first
who classed insects according to their mode of taking their food.

[1184] PLATE VI. VII. XXVI. a´.

[1185] In _Lucanus_, _Lamprina_, &c. the labrum seems to form the
under-side of the nose, and to be connate with it.

[1186] Kirby _Mon. Ap. Angl._ i. _t._ v. _Apis_ *. b. _f._ 18. _b._

[1187] _Ibid. t._ ii. _Melitta_ **. b. _f._ 4, 5. PLATE XXVI. FIG. 30.

[1188] PLATE XXVI. FIG. 31. _Mon. Ap. Angl._ i. _t._ x. _Apis_ **. c.
2. δ. _f._ 13. _c._

[1189] PLATES VI. VII. and XXVI. b.

[1190] De Geer iv. 124. _t._ iv. _f._ 12. iii. 415. _t._ xxi. _f._ 4.

[1191] Ibid. iv. 281--. _t._ xi. _f._ 7.

[1192] Ibid. 329. _t._ xii. _f._ 3.

[1193] Ibid. ii. 775--. _t._ xxvi. _f._ 10. b c, b c.

[1194] _Philos. Entom._ 18.

[1195] _Syst. Eleuth._ i. Præf. iv.

[1196] _Gen. Crustac. et Ins._ i. 180.

[1197] _N. Dict. d'Hist. Nat._ iv. 246.

[1198] PLATE VI. FIG. 6. b´. a´´.

[1199] PLATE VII. FIG. 3. b´. a´´.

[1200] Kirby _Linn. Trans._ xii. _t._ xxi. _f._ 8. _f_.

[1201] Ibid. _t._ xxi. _f._ 10. _d_. MacLeay _Hor. Entomol._ i. _t._
iii. _f._ 26, 27.

[1202] PLATE XXVI. FIG. 35.

[1203] Ibid. FIG. 34.

[1204] PLATE VII. FIG. 3. b´.

[1205] PLATE XXVI. FIG. 24. b´.

[1206] PLATE VII. FIG. 3. a´´.

[1207] _N. Dict. d'Hist. Nat._ xxiv. 171.

[1208] PLATE VI. FIG. 6. e´.

[1209] PLATE VII. FIG. 3. i´´.

[1210] PLATE VI. FIG. 12. e´.

[1211] PLATE VI. FIG. 6. b´.

[1212] Ibid. FIG. 12. b´.

[1213] PLATES VI. VII. XXVI. b´´.

[1214] PLATE VI. FIG. 6. b´´.

[1215] _Hor. Entomolog._ i. _t._ i. _f._ 1. _g_.

[1216] _Ibid. t._ ii. _f._ 18. _g._

[1217] Kirby _Mon. Ap. Angl._ i. _t._ xii. _neut._ _f._ 1. _g._ _c._

[1218] _Ibid._ 93. 103--. _t._ vi. Apis **. b. _f._ 3. _b._ _c._

[1219] _Ibid._ _t._ i. *. a. _f._ 3. _b._

[1220] _Ibid._ _t._ ix. _Apis_ **. c. 2. γ. _f._ 3. _b._

[1221] _Clairv. Ent. Helvet._ ii. _t._ xxiv. _f._ 1. _c._

[1222] PLATE XXVI. FIG. 24, 28. b´´.

[1223] _Mon. Ap. Angl._ i. _t._ ii. _Melitta_ **. b. _f._ 2. _c._

[1224] PLATE XIII. FIG. 2. _Linn. Trans._ xii. _t._ xxi. _f._ 6. _b._

[1225] This is the case with _Oxyporus_ F. PLATE XIII. FIG. 4.

[1226] PLATE VI. FIG. 12. b´´. Latreille, _N. Dict. d'Hist. Nat._
xvii. 545, seems not to regard these as palpi; but from their tubular
form, and insertion in the socket of the labium, it is clear that
they ought to be so considered.

[1227] PLATES VI. VII. XXVI. c´.

[1228] A corresponding articulation takes place between the tibia and
thigh of some of the _Scarabæidæ_, which will be hereafter described.
See PLATE XXVII. FIG. 8-11.

[1229] _Comparaison des Organes de la Mastication des_ Orthoptères, 2.

[1230] _Comparaison des Organes de la Mastication des_ Orthoptères, 2.

[1231] See above, p. 407. note b.

[1232] _Ubi supra_, 4.

[1233] _Ibid._

[1234] _Ibid._ 5.

[1235] Oliv. _Ins._ no. 66. _Prionus. t._ xiii. _f._ 54.

[1236] _Ibid._ no. 83. _Curculio. t._ iv. _f._ 37.

[1237] _Linn. Trans._ xii. _t._ xxi. _f._ 12.

[1238] For Mandibles of _Locusta_ see PLATE VI. FIG. 6. c´. of
_Lampyris_ Oliv. _Ins._ no. 28. _t._ i. _f._ 1. of _Buprestis_,
_Ibid._ no. 32. _t._ iii. _f._ 17. of _Lucanus_, _Ibid._ no. 1. _t._
i-v. and of _Prionus_, _Ibid._ no. 66. _t._ ii. _f._ 8.

[1239] _Gomphosis_ is, when one bone is immoveably fixed in another
as a nail in a board.

[1240] Marcel de Serres _ubi supra._ 7.

[1241] See PLATE XIII. FIG. 7. Kirby _Mon. Ap. Angl._ i. _t._ xiii.
_f._ 13. and _t._ xii. _neut. f._ 10.

[1242] PLATE XXVI. FIG. 19.

[1243] Oliv. _Ins._ no. 42. _t._ i. _f._ 1. and no. 2. _t._ i. _f._
1. b.

[1244] PLATE XXVI. FIG. 16, 18.

[1245] Ibid. FIG. 21.

[1246] _Mon. Ap. Angl._ i. _t._ iv. _Melitta. f._ 5-8.

[1247] Drury _Ins._ ii. _t._ xlviii. _f._ 3. See above, p. 315.

[1248] Oliv. no. 1. _t._ v. _f._ 16. &c. _t._ iii. _f._ 7.

[1249] _Comparaison des Organes_, &c. 7--.

[1250] PLATE VI. FIG. 6. and XIII. FIG. 5. a´´´.

[1251] PLATE VI. FIG. 12. and XIII. FIG. 5. b´´´.

[1252] PLATE XXVI. FIG. 16.

[1253] I was not aware that Knoch had observed this part, till some
time after the publication of my paper _On Mr. William MacLeay's
Doctrine of Affinity and Analogy_ (see _Linn. Trans._ xiv. 105--),
when I happened to meet with it in a letter from a friend, received
more than thirteen years ago; but without any reference to the work
of Knoch, in which it was stated. It was doubtless taken from his
_Beiträge zur Insektengeschichte_.

[1254] _Anat. Comp._ iii. 321--.

[1255] One of those mandibles is represented in PLATE XXVI. FIG. 20.
a´´´. incisive teeth d´´´. molary plate. Comp. _Linn. Trans._ ubi
supr. _t._ iii. _f._ 4. _c a b._

[1256] VOL. II. p. 275--.

[1257] In the _Myrmeleon_, or ant-lion, the suction is promoted by
the action of a piston, that pumps up the juices. Reaum. vi. 369.

[1258] De Geer iv. 386--. _t._ xv. _f._ 10. See above, p. 121.

[1259] PLATE XIII. FIG. 7. _c´´._

[1260] Oliv. _Ins._ no. 42. _Staphylinus._ _t._ i. _f._ 1. b.

[1261] PLATES VI. VII. XXVI. d´.

[1262] PLATE VI. FIG. 3, 6, 12. VII. FIG. 3. c´´.

[1263] PLATE VII. FIG. 3. a´´. e´´. _Mon. Ap. Angl._ i. _t._ xiii.
_f._ 1. _e._

[1264] _Ibid._ _f._ 3. _a._

[1265] Clairv. _Ent. Helvet._ ii. 146. _t._ xxiii. _f._ super. _b._

[1266] _N. Dict. d'Hist. Nat._ iv. 243.

[1267] In _Anoplognathus_, however, though it has neither teeth nor
spines, it is as hard as the mandibles.

[1268] See above, p. 317.

[1269] PLATE XXVI. FIG. 10, 11. d´´´. e´´´.

[1270] Ibid. FIG. 9. d´´´. e´´´.

[1271] PLATE VI. FIG. 6, 12. d´´´. e´´´. Oliv. _Ins._ no. 45.
_Meloe._ _t._ i. _f._ 1. c. These are what Fabricius calls _galeate_
maxillæ, on which he founded his class _Ulonata_.

[1272] PLATE XXVI. FIG. 11. d´´´. e´´´.

[1273] PLATE VI. FIG. 3. d´´´.

[1274] Clairv. _Ent. Helvet._ _t._ i. _t._ xviii. _f._ super. _b._

[1275] Ibid. _t._ xix. _b._ This genus may be the analogue of some
heteromerous one yet undiscovered, as _Calosoma_ is of _Adelium_
(Kirby _Linn. Trans_. xii. _t._ xxii. _f._ 2.)

[1276] Clairv. _Ent. Helvet._ ii. _t._ xxiv. _f._ super. _b._

[1277] PLATE XXVI. FIG. 11.

[1278] Oliv. _Ins._ no. 19. _Trogosita._ _t._ 1. _f._ d. no. 41 bis.
_Dryops. t._ i. _f._ 1. c.

[1279] See above, VOL. I. p. 238.

[1280] Oliv. _Ins_. no. 17. _Ptinus._ _t._ i. _f._ 1. c.

[1281] _Ibid._ no. 60. _Blaps t._ i. _f._ 2. c.

[1282] _Ibid._ no. 88. _Languria. t._ i. _f._ 2. c.

[1283] _Ibid._ no. 89. _Erotylus. t._ ii. _f._ 12. c.

[1284] Oliv. _Ins._ no. 41. _Gyrinus._ _t._ i. _f._ 1. e.

[1285] PLATE XXVI. FIG. 13. _Hor. Entomolog._ i. _t._ iii. _f._ 29,
30. E.

[1286] _Mon. Ap. Angl._ i. _t._ ii. _Melitta_. **. a. _f._ 2. _t._ v.
_Apis_. *. b. _f._ 4. &c.

[1287] Oliv. _Ins._ no. 48. _Cerocoma_. _t._ i. _f._ 1. c.

[1288] PLATE XXVI. FIG. 10-12.

[1289] Clairv. _Ent. Helvet._ ii. _Cicindela_. _t._ xxiv. _f._ super.
_b._ for _Carabidæ_, _Dytiscidæ_, his other plates.

[1290] _Hor. Entomolog._ i. _t._ ii. _f._ 13. E.

[1291] PLATE VI. FIG. 6, 12. f´´´.

[1292] _Hor. Entomolog._ _t._ i. _f._ 3. E.

[1293] _Ibid._ _f._ 4. E.

[1294] Oliv. _Ins._ no. 7. _Hexodon_. _t._ i. _f._ 1. e.

[1295] _Ibid._ no. 3. _Scarabæus_. _t._ l. _f._ 1. f.

[1296] Kirby in _Linn. Trans._ xiv. 102. _t._ iii. _f._ 4. d.

[1297] De Geer v. 417. _t._ iv. _f._ 12.

[1298] PLATES VI. VII. h´´.

[1299] See above, p. 443.

[1300] _Mon. Ap. Angl._ i. _t._ ix. 2. c. 2. β. _f._ 2. _d. g._ 4.
_t._ xii. _neut. f._ 6. _d._ _t._ xiii. _f._ 3. _b._

[1301] Clairv. _Ent. Helv._ ii. _t._ xxiii. _f._ 1.

[1302] PLATE VII. FIG. 3. b´´. h´´.

[1303] PLATE VI. FIG. 12. b´´. f´´´.

[1304] Ibid. FIG. 13. h´´. Savigny _Anim. sans Vertèbr._ l. i. 29--.
_t._ i.-iii. ȯ.

[1305] De Geer vi. _t._ xix. _f._ 4. _d._

[1306] Ibid. _t._ ix. _f._ 8. _b b._ t. xii. _f._ 20. _b._ _t._ xiv.
_f._ 15. _i i._

[1307] PLATE XXVI. FIG. 6.

[1308] Ibid. FIG. 5.

[1309] Kirby _Mon. Ap. Angl._ i. _t._ x. _Apis._ **. c. 2. δ. _f._ 3.
_a._ and **. d. 1. _f._ 1. _d._

[1310] Clairv. _Ent. Helvet._ ii. _t._ xxxi. _f. super. b. Mon. Ap.
Angl._ i. _t._ xiv. _f._ 1. _h. f._ 3, 5. _c._

[1311] See above, p. 317.

[1312] PLATE XXVI. FIG. 1. As the very remarkable maxillary palpi of
that extraordinary Coleopterous genus _Atractocerus_ seem not to have
been so fully described as they deserve, I shall give here a minute
detail of their composition. They consist of _four_ joints: the first
is wide and short, and somewhat platter-shaped; the second is much
smaller and shorter: the third is concavo-convex, or shaped like a
shallow bowl: towards the breast this joint is elevated, and on the
elevated edge sits the last joint, which is longer than all the rest
taken together. In my specimen it points towards the breast; its
under side is entire and slightly curved, but in the upper side are
two rows of lamellæ (_b_), placed alternately _nine_ on each side,
with an odd one at the end: these lamellæ are full of minute papillæ,
and furrowed on the side next the mouth. From between the first pair
a slender exarticulate hairy branch or appendage emerges (_a_), which
forms nearly a right angle with the main stem. The _labial palpi_
appear to consist of _three_ joints; the two first very short, and
the last large, ovate, and acute. This description is not taken from
_A. necydaloides_, but from a Brazilian species more than five times
its size, which I have named _A. grandis_.

[1313] PLATE VI. VII. XXVI. e´.

[1314] PLATE VI. FIG. 6, 12. e´. Cuvier _Anat. Compar._ iii. 347.

[1315] Cuvier _Ibid._

[1316] Huber _Fourmis_, 4--.

[1317] _Anim. sans Vertèbr._ iii. 304.

[1318] See above, p. 440.

[1319] Reaum. v. 309--.

[1320] PLATE XXVI. FIG. 23.

[1321] Clairv. _Ent. Helvet._ ii. Pref. xxii.

[1322] Kirby _Mon. Ap. Angl._ i. _t._ xiv. (1) 2. _b._

[1323] PLATE XXVI. FIG. 24. e´.

[1324] Clairv. _ubi supr._ _t._ xx. _c._

[1325] PLATE XXVI. FIG. 28. e´.

[1326] Kirby _ubi supr._ fig. (8) 1. _c c._ The lateral pieces in the
tongue in _Vespa_ (_Ibid. c c._) have been regarded as lobes of it,
but they are rather _Paraglossæ_.

[1327] PLATE XXVI. FIG. 29. e´.

[1328] Clairv. _ubi supr. t_. xxx. _c._

[1329] Kirby _ubi supr._ no. 2. _f._ 1, 3.

[1330] PLATE XXVI. FIG. 24. _b._

[1331] Kirby _ubi supr. t._ x. _Apis_. c. 2. δ. _f._ 5. _t._ xii.
_neut. f._ 2, 3. _t._ xiii. _f._ 1. _h._

[1332] PLATE XXVI. FIG. 26, 29.

[1333] PLATE XXVI. FIG. 28. i´´.

[1334] Kirby _Mon. Ap. Angl._ i. _t._ xii. _neut._ _f._ 1. _h h._
_t._ xiii. _f._ 1. _f f._

[1335] _Ibid._ _t._ x. **. d, 1. _f._ 2. _b b._

[1336] See above, p. 425.

[1337] PLATE VII. FIG. 14. f´.

[1338] Reaum. v. 317.

[1339] _Organisation exterieur des Ins._ 184.

[1340] _Ubi supra._

[1341] _Anim. sans Vertèbr._ I. i. 12.

[1342] De Geer ii. 778--. _t._ xxvi. _f._ 11. _m._ PLATE VII. FIG. 2.
k´´.

[1343] _Ubi supra._

[1344] See above, p. 455.

[1345] _Organisation_ &c. 182.

[1346] Under this name M. Savigny includes the _Myriapoda_,
_Arachnida_, and _Crustacea_. _Anim. sans Vertèbr._ I. i. 40.

[1347] _Ibid._ 43.

[1348] VOL. II. p. 275--. Also see above, p. 121--.

[1349] _Anim. sans Vertèbr._ I. i. _t._ ii. _f._ 2. a. a´.

[1350] PLATE VII. FIG. 13. c´.

[1351] Ibid. d´.

[1352] _Anim. sans Vertèbr._ I. i. 106. PLATE VII. FIG. 13. b´.

[1353] _Ubi supr._ 45--.

[1354] PLATE VII. FIG. 11. _f´_, _a´´_.

[1355] _Ubi supra_, 45.

[1356] Ibid. 44--.

[1357] _N. Dict. d'Hist. Nat._ ii. 275--. PLATE VII. FIG. 10. c´.

[1358] De Geer _t._ xl. _f._ 4. _t._ x. _f._ 7, 8.

[1359] See above, p. 18, 30.

[1360] Savigny _Anim. sans Vertèbr._ I. i. 62.

[1361] _N. Dict. d'Hist. Nat._ ii. 277.

[1362] _N. Dict. d'Hist. Nat._ ii. 276.

[1363] _Ibid._

[1364] _Ubi supr._ 58.

[1365] PLATE XV. FIG. 7.

[1366] PLATE VI. FIG. 7-9. a´, b´, c´, d´.

[1367] _Magaz._ 1806.

[1368] PLATE VI. FIG. 7. a´.

[1369] Ibid. Labium b´. Mandibulæ c´. Maxillæ d´.

[1370] Savigny _Anim. sans Vertèbr._ I. i. 37.

[1371] De Geer iii. 137--. _t._ ix. _f._ 4.

[1372] Reaum. iii. 335. _t._ xxviii. _f._ 8-14.

[1373] De Geer iii. 117. _t._ viii. _f._ 22. _b._

[1374] PLATE VII. FIG. 5, 6. a´, b´, c´, d´.

[1375] _N. Dict. d'Hist. Nat._ iv. 253.

[1376] PLATE VII. FIG. 5, 6. a´.

[1377] Ibid.

[1378] Reaum. iv. _t._ XVI. FIG. 13. z.

[1379] Authors are not agreed as to the precise number of lancets
contained in a gnat's proboscis. Swammerdam affirms there are _six_,
including the labrum. i. 156. b. _t._ xxxii. _f._ 3. Reaumur could
find only _five_. iv. 597--. _t._ xlii. _f._ 10. And Leeuwenhoeck
only _four_.

[1380] PLATE VII. FIG. 5.

[1381] PLATE VII. FIG. 5. This figure is copied from Reaumur, and was
engraved before this discovery was made.

[1382] M. Savigny is of opinion that the central lancet or lancets
represent the _Epipharynx_ and _Hypopharynx_; for which he does not
state his reasons: but as these are properly covers of the pharynx,
the idea seems incorrect. _Ubi supr._ 15.

[1383] _N. Dict. d'Hist. Nat._ ix. 489. and iv. 253--.

[1384] _Ubi supr._ 36.

[1385] Ibid. _t._ iv. _f._ 1. o. _o._

[1386] VOL. I. p. 48, 110--.

[1387] PLATE VI. FIG. 13. a´, b´, c´, d´.

[1388] VOL. I. p. 394--.

[1389] PLATE VI. FIG. 13. a´. Savigny _Anim. sans Vertèbr._ I. i.
3--. _t._ i.-iii. a.

[1390] _Ibid._ i. PLATE VI. FIG. 13. c´.

[1391] Ibid. FIG. 13. h´´. Savigny _ubi supr. o._

[1392] PLATE VI. FIG. 13. d´. Savigny _ubi supr. t._ 1-3. _o._

[1393] Ibid. _ö._ PLATE VI. FIG. 13. b´.

[1394] _N. Dict. d'Hist. Nat._ xvii. 467.

[1395] _N. Dict. d'Hist. Nat._ iv. 253.

[1396] PLATE VII. FIG. 8. c´, d´, e´, h´´.

[1397] Ibid, c´.

[1398] Ibid, d´.

[1399] Ibid, h´´.

[1400] Ibid. e´.

[1401] Rösel. ii. _t._ iii. _f._ 15. Latreille _Gen. Crust. et Ins._
iv. 365.

[1402] Swammerdam _Bibl. Nat. t._ ii. _f._ 4.

[1403] _N. Dict. d'Hist. Nat._ xxviii. 266.

[1404] _Ibid._ xvi. 432. De Geer vii. _t._ vi. _f._ 4. Not quite
accurate.

[1405] PLATES VI. VII. XXVII. a.

[1406] _Organisat. Extér. des Ins._ 196.

[1407] In the _Transactions of the Royal Society_, this part in
_Anobium tessellatum_ is so called. xxxiii. 159--.

[1408] PLATE XXVII. FIG. 4. a.

[1409] PLATE VII. FIG. 2. a.

[1410] _Observ. Nouv. sur les Hyménoptères_ (_Ann. du Mus._) 5.

[1411] Those beetles whose posterior pair of tarsi have only _four_
joints, and the two anterior _five_, are so called.

[1412] Kirby in _Linn. Trans._ xii. 464. _t._ xxiii. _f._ 6.

[1413] Ibid. xiii. _t._ i. _f._ 1. _b._

[1414] PLATE VI. FIG. 10. g´.

[1415] Ibid. FIG. 7. a.

[1416] Ibid. g´.

[1417] PLATE VI. FIG. 4. g´.

[1418] PLATES VI. VII. b.

[1419] Kirby _Mon. Ap. Angl._ i. _t._ i. _Melitta._ *. b. _f._ 3.

[1420] PLATE VI. FIG. 4. b.

[1421] PLATES VI. VII. c.

[1422] VOL. II. p. 317--.

[1423] PLATE XXVI. FIG. 41. i.

[1424] Stoll _Punaises_, _t._ xxxix. _f._ 279, 280.

[1425] PLATES VI. VII. XXVI. d.

[1426] PLATES VI. VII. e.

[1427] PLATES VI. VII. f.

[1428] PLATE XXVII. FIG. 4. f.

[1429] Cuv. _Regne Animal._ iii. _t._ xiii. _f._ 4.

[1430] This insect was taken both at Matlock and Exmouth. The body
and thighs are of a light-brown, wings testaceous, legs pale; antennæ
between setaceous and filiform, two-thirds the length of the body;
first joint not much thicker than the rest.

[1431] PLATE VI. VII. g.

[1432] De Geer iii. 561. _t._ xxvii. _f._ 1.

[1433] PLATES VI. VII. XXVI. h.

[1434] PLATE VII. FIG. 8, 9. XXVI. FIG. 43. h.

[1435] Viz. one on each side above, and one below.

[1436] Walckenaer _Aranéïdes_, _t._ v. _f._ 50, 52. _t._ viii. _f._ 82.

[1437] Treviranus (_Arachnid_. 4.) says that _Scorpio Europæus_
has only _two_ eyes. He appears to have overlooked the two on the
anterior side of a tubercle at each angle of the head, where they are
large, but not conspicuous, at least in my specimen.

[1438] De Geer vii. _t._ iii. _f._ 8, 9, 12.

[1439] PLATE XXVI. FIG. 43., h.

[1440] Walck. _Aran._ _t._ i. _f._ 3.

[1441] _Ibid._ _t._ v. _f._ 42-48.

[1442] _Ibid._ _t._ iv. _f._ 41.

[1443] Walck. _Aran._ _t._ i. _f._ 2.

[1444] _Ibid._ _t._ i. _f._ 7.

[1445] _Ibid._ _t._ ii. _f._ 18, 20.

[1446] VOL. I. p. 323.

[1447] De Geer vii. 138. _t._ viii. _f._ 15. _y y_.

[1448] Ibid. _t._ xl. _f._ 3. _o o_, _y y_.

[1449] PLATE XXVI. FIG. 43. h.

[1450] _Segestria perfida_, Walck. _Aran._ _t._ v. _f._ 52. &c.

[1451] _Tetragnatha_ and _Latrodectes_, _Ibid._ _t._ vii. _f._ 64.
and _t._ ix. _f._. 84.

[1452] _Nyssus coloripes_, _Ibid._ _t._ vi. _f._ 58.

[1453] _Dolomeda_, _Ibid._ _t._ ii. _f._ 18, 20.

[1454] _Sphasus_, _Ibid._ _t._ iii. _f._ 24.

[1455] _Mygale avicularia_, _Ibid._ _t._ i. _f._ 3.

[1456] _Sparasus_, _Ibid._ _t._ iv. _f._ 41. PLATE XXVI. FIG. 37.

[1457] _Eresus_, _Ibid._ _t._ iii. _f._ 26.

[1458] _Storena_, _Ibid._ _t._ ix. _f._ 86.

[1459] _Argyroneta_, _Ibid._ _f._ 88.

[1460] _Pholeus_, _Ibid._ _t._ viii. _f._ 80.

[1461] PLATE XIII. FIG. 11.

[1462] PLATE XXIX. FIG. 11. h.

[1463] Ibid. _a._

[1464] PLATE XIII. FIG. 10.

[1465] See above, p. 117--.

[1466] Reaum. iv. 245.

[1467] _Microgr._ 176.

[1468] _Epist._ Mar. 6. 1717.

[1469] _Amœn. Academ._ vii. 141.

[1470] I possess a specimen in which the eye is partly black and
partly white: the lenses are invisible in the _black_ part, but very
visible in the white.

[1471] _Philos. Entomolog._ 19.

[1472] PLATE XXVI. FIG. 38.

[1473] Hooke _Microgr._ schem. xxiv.

[1474] PLATE XXIII. FIG. 3.

[1475] Cuvier _Anat. Compar._ ii. 442--. Compare Swammerdam _Bibl.
Nat._ i. 211. _t._ xx. _f._ 45.

[1476] VOL. II. p. 4, 364, &c.

[1477] PLATE XXVI. FIG. 36. h. Fabricius, and after him Olivier,
though both quote Forster, regard one of these eyes in _Lamia
Tornator_ as a spot; but they could not have examined it attentively.
_Saperda præusta_ F. has also four eyes.

[1478] PLATE XXVI. FIG. 39. h.

[1479] Latreille _Gen. Crust. et Ins._ iii. 73.

[1480] _N. Dict. d'Hist. Nat._ i. 479.

[1481] VOL. II. 320.

[1482] De Geer vii. 562.

[1483] VOL. II. p. 228.

[1484] _Ent. Helvet._ i. _t._ xii.

[1485] PLATE VI. FIG. 10.

[1486] Kirby _Mon. Ap. Angl._ i. _t._ xi. _Apis._ **. e. 1. _f._ 2.

[1487] De Geer iii. _t._ xxxiv. _f._ 17, 18, 24. _o o._

[1488] _Mon. Ap. Angl._ i. _t._ xiv. no. 11. _f._ 1. _f._ _Linn.
Trans._ xi. _t._ ix. _f._ 10. d.

[1489] PLATE XIII. FIG. 9. Fuessly _Archiv._ _t._ vi.

[1490] Schellenberg _Cimices_ _t._ xiii. ix. _f._ 1. _a._ De Geer ii.
_t._ xviii. _f._ 10.

[1491] Stoll _Spectres_, &c. _t._ iv. _f._ 14. _t._ x. _f._ 38, &c.

[1492] VOL. I. p. 261--.

[1493] _Linn. Trans. ubi supr._

[1494] Schellenberg _Mouches_, _t._ xxvii. _f._ 1, 2. _a, d._

[1495] _Ibid._ _t._ ix. _f._ 3. _a._

[1496] _Ibid._ _t._ ii. _f._ 2. _a._

[1497] _Mon. Ap. Angl._ i. 148.

[1498] PLATE XXVII. FIG. 4. h´.

[1499] This circumstance proves that Mr. W. S. MacLeay is correct in
considering this as a subgenus; but it militates against its being
connected with _Lamprima_.

[1500] PLATE VI. FIG. 4, 10. VII. FIG. 1, 2, 4. XXVI. FIG. 39-42. i.

[1501] _Bibl. Nat._ i. 214.

[1502] Reaum. iv. 245.

[1503] Ibid. v. 287--.

[1504] _Magas. der Entomolog._ iv. 410.

[1505] Latreille speaks of _Phasma_ as having no stemmata; but it
should seem that he examined only the _apterous_ ones, all the
_winged_ individuals, at least so far as I have examined them,
having three very visible ones. It may, I think, be laid down as a
rule, that the larvæ and pupæ of _Orthoptera_ have not these organs.
Probably their use is principally in flying?

[1506] _Flata phalænoides_ F. and affinities have no stemmata, while
_Flata reticulata_ and affinities have them: a proof that these
tribes are distinct genera.

[1507] PLATE VI. FIG. 10. i.

[1508] Reaum. iv. 243. He refers for this insect to plate xiv. without
adding any number for the figure; but no such is in that plate.

[1509] PLATE XXVI. FIG. 40. i.

[1510] _Cercopis_, Ibid. FIG. 42; and _Fulgora_, FIG. 41. i.

[1511] PLATE VI. FIG. 4. i.

[1512] PLATE XXVI. FIG. 40. i.

[1513] Ibid. FIG. 42. i.

[1514] PLATE XXVI. FIG. 41. i.

[1515] De Geer iii. _t._ xxvii. _f._ 1. Reaum. iii. _t._ xxxii. _f._
3, 9.

[1516] PLATE XXVI. FIG. 40. i.

[1517] See above, p. 318--.

[1518] _Linn. Trans._ xiii.

[1519] _Mag. der Entomolog._ iv. 5.

[1520] Palpi quatuor, subæquales, cylindrici, _ad basin clypei. Germ._

[1521] See above, p. 18, &c.

[1522] PLATE VI. FIG. 1, 4. i´.

[1523] See above, p. 321. _Linn. Trans._ xii. _t._ xxi. _f._ 3.

[1524] Ibid. _f._ 7.

[1525] PLATE VI. FIG. 4. c. i´.

[1526] PLATE XII. FIG. 9. l´´. This circumstance was very recently
discovered; which will account for this plate not being quite correct
in this respect, the bulb being represented as a distinct joint in
FIG. 6, 10, 26.

[1527] See above, p. 498.

[1528] VOL. I. p. 231, 238.

[1529] Oliv. _Ins._ no. 80. _Macrocephalus t._ i. _f._ 1-4.;
_Anthribus f._ 5-12; and no. 83. _Curculio t._ ii. _Calandra f._ 16.

[1530] Schellenberg _Cimices t._ xiv. _f._ 1. _b._

[1531] De Geer vii. _t._ iv. _f._ 7. _a a._

[1532] VOL. II. p. 421.

[1533] PLATES XII. FIG. 28; and XXV. FIG. 9, 24.

[1534] PLATE XXV. FIG. 4.

[1535] PLATES XII. FIG. 29; and XXV. FIG. 28. _a._

[1536] PLATES XI. XII. XXV. k´´.

[1537] PLATES XI. XII. XXV. l´.

[1538] Ibid. m´.

[1539] PLATES XII. FIG. 28; and XXV. FIG. 13. m´´.

[1540] PLATE XXV. FIG. 2, 5, 21. m´´.

[1541] PLATE XII. FIG. 10. m´´.

[1542] Ibid. FIG. 4. m´´.

[1543] PLATE XXV. FIG. 1. m´´.

[1544] PLATE XI. FIG. 23.

[1545] PLATE XXV. FIG. 24.

[1546] Ibid. FIG. 30.

[1547] Jurine _Hymenopt._ _t._ vii. _f._ 3.

[1548] PLATE XXV. FIG. 28.

[1549] Ibid. FIG. 13.

[1550] Ibid. FIG. 5.

[1551] Ibid. FIG. 1.

[1552] PLATE XI. FIG. 12.

[1553] _Linn. Trans._ xii. _t._ xxi. _f._ 3.

[1554] Latreille says _six_, but only _five_ are discernible; the
three last form a kind of bristle.

[1555] Latr. _Fourmis_, 323.

[1556] Jurine _Hymenopt._ _t._ vi. _f._ 3.

[1557] _Ibid._ _f._ 2.

[1558] _Ibid._ _f._ 1. PLATE XXV. FIG. 7.

[1559] PLATE XXV. FIG. 25, 26.

[1560] PLATE XII. FIG. 16-22.

[1561] Ibid. FIG. 19. _a_.

[1562] _Linn. Trans._ xxii. _t._ xxi. _f._ 3, 4. PLATE XXV. FIG. 11.

[1563] PLATE XI. FIG. 17.

[1564] Kirby _Mon. Ap. Angl._ i. 184. _t._ x. **. d. 1. f. 8.

[1565] PLATE XXV. FIG. 27.

[1566] PLATE XII. FIG. 26.

[1567] PLATE XXV. FIG. 32.

[1568] PLATE XII. FIG. 25.

[1569] PLATE XXV. FIG. 17.

[1570] _Linn. Trans_. xii. _t._ xxiii. _f._ 5. _f._

[1571] _Ibid. t._ xxi. _f._ 8 _g._ 9, 10. _c._

[1572] De Geer iv. 219. _t._ viii. _f._ 20.

[1573] See VOL. II. p. 65, 201--.

[1574] De Geer iv. _t._ vii. _f._ 22.

[1575] PLATE XXV. FIG. 35.

[1576] De Geer vi. _t._ i. _f._ 5.

[1577] PLATE XI. FIG. 21.

[1578] PLATE XII. FIG. 29. _a._

[1579] PLATE VI. m.

[1580] Ibid.

[1581] PLATE XXVII. FIG. 1, 3-5. n´.

[1582] Ibid. FIG. 3.

[1583] Ibid. FIG. 4.

[1584] PLATE XXVII. FIG. 1.

                              LETTER XXXV.

                     _EXTERNAL ANATOMY OF INSECTS_,
                               CONTINUED.

                  THE TRUNK, AND ITS PARTS AND ORGANS.

As the _head_ of insects is the principal seat of the organs of
_sensation_, so is the _trunk_ of those of _motion_; and in it are
contained the muscles by which they are moved: it may therefore be
regarded as the great centre of motion, and as the main support and
prop of the two other primary sections of the body--the head and
abdomen, between which it is situated--it may be deemed the most
important part of the insect, the key-stone of the whole structure.
In treating upon it, for the greater clearness, I shall consider its
_substance_, _general form_, _proportions_, _composition_, _internal
processes_, and _members_. It will first, however, be necessary to
assign my reasons for the nomenclature of its parts that I have adopted.

Had the entomological world been universally agreed upon this
subject, and there was an established system of Orismology[1585],
I should have proposed no alteration without great reluctance, and
the fullest conviction of the absolute necessity of some change;
but as the standard of language in our science is still unsettled,
and different terms are used by different writers, there seems full
liberty left to me to select those that appear upon the whole most
appropriate; and where proper and significant terms seem wanting, to
invent new ones. M. Latreille, in a late Essay[1586], has proposed
many changes of this kind, and seems to hesitate concerning the
adoption of some of those recently coined in France for the parts of
the trunk[1587]; it may therefore, I think, be permitted me to labour
a little in this hitherto imperfectly cultured field, and to suggest
such improvements as the subject may seem to require or admit.

Linné called the part we are now considering the _trunk_, its
upper-side he usually denominated the _thorax_, and its under-side
the _breast_: he notices also the _scutellum_ and _sternum_[1588].
As the _prothorax_ and _scutellum_ are the only _apparent_ parts of
the back of the trunk in his first Orders (_Coleoptera_, _Hemiptera_
L.), the rest being covered, in noticing these he puts the part for
the whole, calling the _prothorax_ the _thorax_, but which strictly
was not synonymous with what he called by the same name in the other
Orders. Linné's phraseology with regard to the trunk of insects was
adopted by Fabricius and other Entomologists, till Illiger employed
the term _thorax_ to designate the whole of the trunk[1589], calling
the upper part _thorax superior_ and the lower _thorax inferior_.
M. De Blainville, M. Latreille, and other French writers, improved
upon this, naming the upper part the back (_dorsum_), and the lower
the breast (_pectus_); and dividing the trunk, or according to
them _thorax_, into three sections, each bearing a pair of legs.
But I see no sufficient reason for this alteration--the terms
_trunk_, _thorax_, and _breast_, in the common acceptation are well
understood, and lead to no confusion or glaring impropriety; I
shall therefore adhere to the old phraseology, especially as French
Entomologists in popular language still do the same.

As to the division of the trunk into segments by M. Latreille and
others, it has been regarded as consisting of _three_ primary ones,
which have been called in the order of their occurrence, reckoning
from the head--_prothorax_, _mesothorax_, _metathorax_. The first
of these segments, however--and the learned Entomologist just named
seems to hint as much[1590]--is usually more distinct from the other
two, than they are from each other. If this idea be correct, the
trunk is properly resolvable into _two_ primary segments, the first
bearing the arms or fore-legs, and the other the proper legs and
the organs of flight. M. Chabrier calls the latter _tronc alifère_,
or wing-trunk;--a happy term, which I have adopted and latinized,
calling it the alitrunk (_alitruncus_): the first segment, because
it bears the fore-legs, I have named manitrunk (_manitruncus_). I
adopt likewise the terms above mentioned, _prothorax_, _mesothorax_,
_metathorax_, to signify the three segments into which the thorax of
Linné, or the _upper_ side of the trunk, is resolvable; and those of
the breast I denominate _antepectus_, _medipectus_, and _postpectus_.
If terms be thought necessary to designate the two intire segments
into which the alitrunk is resolvable, the first may be the meditrunk
(_meditruncus_), and the other the potrunk (_potruncus_).

I. _Substance._--With regard to its _substance_, the trunk in general
is softer than the head, and harder than the abdomen, especially as
to its upper surface; but in some cases, where it is not protected by
the elytra, as in the rove-beetles (_Staphylinus_ L.), the abdomen
appears as hard as the trunk. Though usually not very different from
the elytra in this respect, in _Meloe_, _Lytta_, and other vesicatory
beetles, it is of a firmer consistence.

II. _General Form._--In the _Coleoptera_ Order the only part of
the trunk that is visible on its upper-side is the _prothorax_:
the _mesothorax_, with the exception of the _scutellum_, and the
_metathorax_, being entirely concealed by it and the elytra; so that,
with regard to _shape_, it may nearly be considered as merging in the
_prothorax_. Below it is more visible, and may be stated as more or
less quadrangular; in oblong beetles inclining to a parallelogram,
and in shorter or hemispherical ones to a square. In the majority
it is more convex below than above, except in the case of the
hemispherical or gibbous beetles (_Coccinella_, _Erotylus_, &c.), in
which the under-side is flat and the upper-side very convex. In the
_Diurnal Lepidoptera_ the trunk approaches to a cubical shape, in the
_Nocturnal_ it is more spherical. A similar difference obtains in
the _Hymenoptera_ and _Diptera_: in the bees, wasps and flies, the
trunk approaching to the figure of a sphere; in the ants, _Scoliæ_,
crane-flies, &c. to that of a cube. The upper part of it in many
_Ichneumonidæ_, female ants, &c. is very elevated, forming an arch,
and sloping towards the abdomen. In general it may be observed with
respect to the remaining Orders, that the form of the trunk merges
in that of the whole body, the tendency of which is often to a
three-sided figure.

III. _Proportions._--The trunk is usually longer and larger than
the head and longer than the abdomen, but not wider: but there are
exceptions to both these rules. In _Colliuris_, _Mantis_, &c.,
it is more _slender_; and in _Atta megacephala_ and some neuter
ants, it is _shorter_ than the _head_; in _Atractocerus_, many
_Staphylinidæ_, _Phasma_, the _Libellulina_, the _Lepidoptera_, and
various _Hymenoptera_, it is shorter, and in the _Mantidæ_ more
_slender_ than the _abdomen_. The greatest disproportion between it
and the last part is exhibited by the genus _Evania_, parasitic upon
the _Blattæ_, in which the abdomen appears merely as a minute and
insignificant appendage of the trunk. The vertical diameter of this
part, almost without exception, is greater than that of either head
or abdomen. When we consider that it contains the muscles that move
both the organs of flight and the legs, we see clearly the reason why
the CREATOR gave it greater volume.

IV. _Composition._--I lately intimated to you that the trunk, though
resolvable into _three_ segments, in most cases properly consists
of only _two_ primary ones. Whoever examines the perfect insects of
every Order, except the _Aptera_[1591], will find this distinction
strongly pointed out, not only by the different direction of the
first pair of legs from that of the two last, but also in a large
proportion by a deep incisure; and in all it is further manifested
by the anterior segment having a motion distinct from that of the
rest of the trunk, and separating readily from it; and this not only
where it is large, as in insects that have a thoracic shield, but
also in those in which the _prothorax_ is less apparent: whereas the
other two pedigerous segments have little or no distinct motion,
will not readily separate from each other, and in some cases exhibit
no pectoral suture between them. Sometimes, however, these two last
segments are more prominently distinguished: in _Lytta_, _Mylabris_,
and other vesicatory beetles, they are separated below by an
incisure, or rather the first or mid-leg segment, is not nearly so
elevated as that of the hind-legs. In some ants (_Atta_ Latr.), in
the neuters, there is no distinction of segments in the trunk; but
in others (_Formica_ Latr.) it follows the general law, and consists
of three. In the _Arachnida_, with the exception of _Galeodes_, in
which the head is distinct, and the three segments of the trunk may
be traced, these parts together form only a single segment. Induced
by these reasons, I consider the trunk as consisting in general of
two _primary_ segments, the _manitrunk_ and _alitrunk_: the latter
resolvable into two _secondary_ ones.

* _Manitruncus_[1592].--The manitrunk, then, is the anterior section
of the trunk, which bears the arms and contains the muscles that move
them. This part has free motion, or a motion independent of that of
the rest of the trunk. This indeed seems a necessary result of the
direction and uses of the arms. It consists of an upper and lower
part--the _prothorax_ and _antepectus_.

i. _Prothorax_[1593].--The upper part of the manitrunk in the
_Coleoptera_, _Orthoptera_, and _Hemiptera_, is by far the most
conspicuous part of the trunk, but in the other Orders it is less so.
With respect to it, insects may be divided into two classes--those
that have and those that have not a _prothorax_. In the _Coleoptera_
Order it is remarkable both for size and variations in its shape and
sculpture. In the _Orthoptera_, though less various, it is almost
equally conspicuous, especially in _Blatta_. In the _Homopterous_
section of the _Hemiptera_, in many genera it has become extremely
short; while in the _Heteropterous_ section its dimensions are not
much reduced. In the majority of the _Neuroptera_, likewise, it is
comparatively large; in the _Libellulina_ much shorter, and in the
_Trichoptera_ and _Lepidoptera_ nearly evanescent[1594].--In the
_Hymenoptera_ and _Diptera_, with very few exceptions, the thoracic
shield altogether disappears, at least if I am correct in an idea,
which I shall hereafter explain, that the _collar_ usually regarded
as the analogue of the _prothorax_, is really a part of the alitrunk.
In these last Orders, though there is no true _prothorax_, the
manitrunk still remains under the form of an _antepectus_, bearing
the fore-legs, and containing the muscles that move them.

The prothorax of insects may in general be considered with respect
to its _parts_, _margin_, _appendages_, _shape_, _sculpture_,
_clothing_, and _proportions_.

1. The _prothorax_, regarded as a whole, distinct from the
_antepectus_ or fore-breast, consists commonly of _two_ pieces--the
_shield_, or upper part[1595], and the _ora_, or under part[1596].
In the shield you are to observe its _apex_[1597], _base_[1598],
_sides_[1599], _limb_[1600], and _disk_[1601]. The _apex_ is the
part next the _head_; the _base_ that next the _abdomen_; the
_limb_ the _circumference_, and the _disk_ the _central_ part. In
many _Orthoptera_ and Heteropterous _Hemiptera_, the shield appears
further to consist of two pieces, an anterior and posterior one.
The _ora_ is a continuation of the shield below the lateral margin,
turned downwards and inwards towards the fore-breast and the legs,
but separated from the former in most cases by a suture, as in
_Carabus_ L.; and in others merely by an impressed line, as in
_Blaps_ F.; but in _Curculio_ and _Cerambyx_ L., &c. there is no ora,
the shield being without a lateral margin, and forming one piece with
the _antepectus_. The part we are now considering varies in different
genera. Sometimes it is very _narrow_, as in _Scarites_; at others
very _broad_, as in _Buprestis_, _Nepa_, &c. In _Lampyris_, except
_L. italica_, and affinities, it projects posteriorly into a _lobe_
or tooth, which forms a right angle with the rest of the _ora_, and
becomes the lower part of the cavity that receives the head; and in
_Dermestes_ this part is excavated into an anterior and posterior one
which admits the antennæ and arms when folded for repose.

2. The _margin_ of the _prothorax_ is a ridge, either defining its
sides or whole circumference. In many cases this margin is broad and
dilated, but in others it is merely a thread or bead that separates
the shield from the _ora_. Though generally terminating the upper
surface, it sometimes, as in _Staphylinus_, dips below it. In many
insects, however, as I just observed, the thoracic shield has no
lateral margin whatever.

3. Various and singular are the _appendages_ with which the
_prothorax_ of numerous insects is furnished. Many of these are
_sexual_ distinctions, and have been before described to you[1602];
but there are others common to both sexes, the most remarkable of
which I shall notice.--Some are distinguished by a long _horn_ which
overhangs the head, as _Membracis cultrata_, _ensata_, &c.[1603];
in others it stands upright, as in _Centrotus spinosus_[1604];
_C. Taurus_ has a pair of thoracic horns like those of a bull,
only dorsal[1605]; in _Ledra aurita_ they are flat, and represent
ears[1606]; in some species of _Tingis_ (_T. Echii_, _Pyri_, &c.)
a kind of reticulated hood, resembling lace, is elevated from the
anterior part of the _prothorax_, which receives and shelters the
head[1607]. In _Centrotus globularis_ and _clavatus_ F., especially
the former, the part in question is armed by a most singular and
wonderful apparatus of balls and spines,--in one case standing
erect[1608], and in the other being horizontal[1609],--which gives
these animals a most extraordinary appearance. In many of the species
here quoted the _prothorax_ is producted posteriorly into a long
scutelliform horizontal horn, which more or less covers the wings and
abdomen; a circumstance which also distinguishes the genus _Acrydium_
F. (_Tetrix_ Latr.). This horn seems to have been sometimes regarded
by Linné and Fabricius as a real _scutellum_, and sometimes only as
a process of the prothorax: but that it is merely the latter will be
evident to you, if you examine carefully any insect furnished with
this appendage; for if you remove that part, you will discover the
true scutellum and other parts of the trunk concealed beneath it. A
very remarkable prothoracic appendage is exhibited by some species
of _Mantis_. In general the part we are treating of in this tribe is
very slender; but in _M. strumaria_, _gongyloides_, &c., it appears
dilated to a vast width, and assumes, either partially or generally,
a subrhomboidal form; but if it is more closely examined, it will be
found that the form of the _prothorax_ is really similar to that of
the rest of the tribe, but that this part is furnished on each side,
either on its whole length or anteriorly, with a large membranous
flat subtriangular appendage resembling parchment[1610]. Perhaps
this kind of sail may be useful to the animal in flight. In _Prionus
coriarius_ &c. its sides are armed with teeth, and in many _Lamiæ_,
_Cerambyces_, and other Capricorn beetles, and often in various bugs
(_Pentatoma_ Latr.) with sharp fixed spines. But the _prothorax_
has _moveable_ as well as _fixed_ appendages; of this kind are
those spines (_umbones_), whose base is a spherical boss moving in
an _acetabulum_ of the thoracic shield of the Capricorn subgenus
_Macropus_ Thunb. If I might hazard a conjecture, I should say that
these organs were given to this animal by an all-provident CREATOR,
to enable it to push itself forward, when in the heart of some tree
it emerges from the pupa, that it may escape from its confinement.
Another kind of moveable appendages are attached to the thorax of
_Lepidoptera_, usually in the form of a pair of concavo-convex scales
covered externally with a tuft of hairs[1611]. M. Chabrier, who
examined these scales in recent insects, describes them as vesicles,
which appeared to him full of a liquid and of air, and capable of
being alternately inflated and rendered flaccid; he regards them
as accessories to a pair of spiracles, which he looks upon as
vocal[1612], opening into the manitrunk just above the insertion of
the arms. These organs are quite distinct from the _tegulæ_ that
cover the base of the primary wings of insects of this Order[1613],
and are what, borrowing a term from Mouffet[1614], I have called in
the table _patagia_, or tippets. Under this head I may include the
_caruncles_ at the anterior angles of the _prothorax_ of a genus
of beetles with soft elytra, named by Fabricius _Malachius_. When
pressed, says De Geer of these insects, a red inflated soft vesicle,
of an irregular shape, and consisting of three lobes, emerges from
the thorax and from each side of the anterior part of the abdomen,
which re-enters the body when the pressure is removed[1615]. M.
Latreille seems to think that these vesicles have some analogy with
the poisers of _Diptera_ and the pectens of scorpions; and that they
are connected with the respiration[1616].

4. We are next to say something upon the _shape_ of the _prothorax_.
The forms of the thoracic shield, especially in the _Coleoptera_,
are so various, that it would be endless to aim at particularizing
all; but it may be useful to notice a few of the most remarkable. The
prothorax of _Moluris_, a darkling-beetle, approaches the nearest
of that of any insect to a spherical form, from its remarkable
convexity; in the wheel-bug (_Reduvius serratus_) it is compressed,
and longitudinally elevated into a semicircular serrated crest: it
is crested, also, in many _Locustæ_ and _Acridæ_, in some having
two parallel ridges; but, generally speaking, its surface is
more depressed. In _Necrodes_ it is nearly circular, in _Blatta
petiveriana_ semicircular, in _Nilion_ and some _Coccinellidæ_
crescent-shaped, in _Carabus_ obcordate, in _Cantharis_ and _Sagra_
approaching to a square, in _Languria_ to a parallelogram; in many
_Cimicidæ_, _Belostoma_, &c., it is triangular, with the vertex
truncated; it is trapezoidal in _Elater_, in _Ateuchus_ rather
pentagonal, and exhibiting an approach to six angles in some
other beetles[1617]: but the prothorax most singular in form is
that of some species of M. Latreille's genus _Helæus_[1618], as
_H. perforatus_, _Brownii_, &c.: in these its anterior angles are
producted, and curving inwards, lap at the end one over the other,
so as to form a circular orifice for the head, which otherwise would
be quite covered by the shield. Thus the upper portion of the eyes
can see objects above, as well as their lower portion those below. I
might enumerate many other forms, but these are sufficient to give
you some notion of the variations of this part.

5. The _prothorax_ is equally various in its _sculpture_; but since
in the Orismological table almost every instance of it has its place,
I shall here only notice it as far as it is common to the whole
tribes, genera, or subgenera. The _Scarabæidæ_ of Mr. W. S. MacLeay
are distinguished by a small _excavation_ on each side of this part,
which, as has been before remarked[1619], furnishes an elevated base
for an internal process with which the anterior _coxæ_ ginglymate. In
_Onitis_ and _Phanæus_, to these excavations are superadded a pair
impressed in the base of the _prothorax_, just above the scutellum;
in _Carabus_ L. a longitudinal channel divides the thoracic shield
into two equal portions; and many genera of that great tribe have
in addition, at the base on each side, one or two excavations or
short furrows. _Elophorus_ F. has on this part several longitudinal
channels, alternately straight and undulated. Generally speaking,
in _Carabus_ L. the _prothorax_ has no impressed points; but in
one or two subgenera of _Harpalidæ_ (_Chlænia_ &c.) it is thickly
covered with them. In numbers of _Locusta_ Leach, the part we are
considering is what Linné terms _cruciate_, being divided into four
longitudinal portions by three elevated lines, the intermediate one
being straight, and the lateral ones diverging from it both at their
base and apex, so as to form a sinus or angle[1620]. In certain
_Acridæ_ K. (_Locusta_ F.) there are only two of these lines or
ridges, but notched or toothed; and in some of the genus first named
only one[1621]; in _Locusta Dux_ and affinities the _prothorax_ has
several transverse channels or rather folds[1622], with corresponding
ridges on its internal surface.

6. With respect to the _clothing_ of the _prothorax_, I have not
much to say: in Coleopterous insects this part is commonly naked;
but in some genera, as _Byrrhus_, _Anthrenus_, _Dermestes_, and many
weevils (_Curculio_ L.) it is partially or totally covered with hairs
or scales. In the other thoracic Orders it is usually naked, but in
some _Neuroptera_, the _Myrmeleonina_, &c., it is hairy; and in the
_Libellulina_ it is fringed posteriorly with hairs.

7. As to its relative _proportions_, the _prothorax_ is sometimes
rather wider than the rest of the trunk and the head, as in _Onitis_,
_Pasimachus_, &c.; it is considerably narrower in _Collyuris_
and _Odacantha_; and of the same width in those _Scaritidæ_ with
_striated_ elytra[1623]. Again, it is sometimes of the same width
with the elytra, but wider than the head, as in _Hydrophilus_,
_Dytiscus_, &c.; in some instances it is of the same width with the
head, and narrower than the elytra, for instance in _Anthia_ and
_Brachinus_. In most _Coleoptera_ it is longer than the head and
shorter than the elytra; but in _Manticora_, the vesicatory beetles,
&c., it is shorter than either. In _Gnoma longicollis_[1624],
it is nearly as long as the elytra; in many _Staphylinidæ_,
_Atractocerus_, &c., longer; in _Phanæus carnifex_, _bellicosus_,
&c., it is longer than the elytra and the rest of the body. With
regard to itself, it is sometimes very wide in proportion to its
length--_Dytiscus_, _Helæus_; at others very long in proportion to
its width--_Colliuris_, _Brentus_, _Mantis_, &c. In _Flata_, and
many other Homopterous _Hemiptera_, it is extremely short; extremely
long in _Gnoma_; in _Sagra_ and _Donacia_ its width about equals its
length; in _Elater_, _Dytiscus_, and many Heteropterous _Hemiptera_,
it is narrowest before; in _Languria_ it is every where of equal
width; in _Anthia_, _Carabus_, &c., it is widest before; and, lastly,
in the _Scarabæidæ_ MacLeay it is usually widest in the middle.

ii. _Antepectus_[1625].--The _antepectus_, as was before
observed[1626], in some tribes forms one piece, without any kind of
separation, with the _prothorax_; but very often this is not the
case. In _Carabus_ L. it occupies almost the whole under-side of
the manitrunk; but in _Elater_, in which the _ora_ is very wide,
the _antepectus_ is merely the _middle_ portion of that part. In
_Carabus_ F. &c. between the _ora_ and the base of the arms is
a convex triangular piece, distinguished from the rest of the
_antepectus_ by a spurious suture; and in _Pentatoma_ and other
Heteropterous _Hemiptera_ a similar piece is observable, which
terminates in a convex bilobed subtriangular sheath, receiving the
base of the clavicle[1627]. This piece seems a prop to that part,
and analogous to the _scapula_ of the _medipectus_ and _parapleura_
of the postpectus. I shall say no more upon the _antepectus_, as it
is seldom remarkable. In the mole-cricket, however, one peculiarity
distinguishes it: it is in this of an elastic leathery substance,
while the _prosternum_ is hard, resembling a bone. In other instances
these parts are both of the same substance.

1. The _sternum_ or breast-bone of insects consists mostly of
_three_ distinct pieces; in this resembling the human _sternum_,
which is described by anatomists as composed originally of _three_
bones[1628]. Each of these pieces is appropriated to a pair of legs,
and each of them at times has been called the _sternum_: thus in
_Elater_ the _prosternum_, in the _Cetoniadæ_ the _mesosternum_,
and in _Hydrophilus_ the _metasternum_, have been distinguished by
this name. Our business is now with the first of these pieces, the
_sternum_ of the _antepectus_ or _prosternum_[1629]: this is the
middle longitudinal ridge of the _fore-breast_, which passes between
the arms, when elevated, extended, or otherwise remarkable. It is
most important in the _Coleoptera_ Order, to which my remarks upon it
will be chiefly confined. In these it is sometimes an _elevation_,
and sometimes a _horizontal_ process of the fore-breast. If you
examine the great _Hydrophilus_ (_H. piceus_), at first you will
think that there is only a single _sternum_ common to all the legs;
but if you look more closely, you will perceive between the head
and the arms a triangular vertical process, with a longitudinal
cavity on its posterior face, which receives the point of the
_mesosternum_ that passes between the arms[1630]: this vertical piece
is the real _prosternum_, and not the other, which really belongs
to the alitrunk. In this case the elevation of the _prosternum_
is _before_ the arms; in others it is _between_ them, as you may
see in a Chinese chafer (_Mimela_ K.), which imitates the external
appearance of a quite different tribe[1631]; in others again it is
_behind_ them, as in most of the Lamellicorn beetles. In the common
dung-chafer (_Geotrupes stercorarius_), it is a hairy process, which,
when the head is bent downwards, is received by a deep cavity of
the _mesosternum_. The _Dynastidæ_ MacLeay may always be known by
a columnar _prosternum_ rising vertically between the arms and the
_medipectus_. Lastly, in other tribes there is a prosternal elevation
both _before_ and _behind_ the arms, as in _Cerambyx thoracicus_,
_dimidiatus_, and affinities. Of the _second_ description, those that
have a less elevated horizontal _prosternum_, the point in most is
to the _anus_, but in some to the _head_: thus in _Carabus_ L. it
is generally a subspathulate flat piece, the point of which slides
over the _mesosternum_, or covers it; but in _Harpalus megacephalus_
Latr.[1632], one of this tribe, though similarly shaped, its point
is to the _head_. These horizontal _prosterna_ vary in their
termination. In that of _Carabus_ L. the apex is obtuse; in that
of _Elater_, above described[1633], and _Dytiscus_ it is _acute_;
in _Prionus lineatus_, _Spencii_ K., &c., it is _bilobed_; and in
_Buprestis variabilis_, _attenuata_, &c., obsoletely _trilobed_.
With regard to the other Orders no striking features of this part
are observable, except in some _Orthoptera_. In _Acrida viridissima_
K. (_Locusta_ F.) it is represented by two long filiform vertical
processes; and in _Locusta_ Leach by a single conical horn[1634],
mistaken by Lichtenstein for a process of the throat[1635]. In
one instance, _Gryllotalpa_, this part is a long piece between
the arms, shaped like the human thighbone or _tibia_, being more
slender in the middle and widest at the ends, and which is of a much
harder substance than the rest of the _antepectus_, and forms the
lower termination of a singular machine which will before long be
noticed. In many bugs (_Cimicidæ_), instead of being elevated, the
three portions of the _sternum_ are hollowed out into a longitudinal
groove, in which the _promuscis_ when unemployed reposes.

The most conspicuous and remarkable appendages of the manitrunk,
are the _brachia_ or arms. I shall not, however, enter into the
full consideration of these, as they consist numerically of the
same parts, till I treat of the legs in general. Here it will
only be necessary to assign my reasons for calling them by a
distinct denomination. In this I think I am authorized, not only
by the example of Linné, who occasionally found it necessary to do
this[1636], and more particularly by the ancient notion that this
pair of organs in insects were not to be reckoned as _legs_[1637],
but likewise from their different position and functions. They are
so inserted in the _antepectus_ as to point towards the _head_,
whereas the other two pair point to the _anus_. With regard to their
_functions_, besides being _ambulatory_, and supporting the manitrunk
in walking, they are applied to many other purposes independent of
that office,--thus they are eminently the _scansory_ or climbing legs
in almost all insects; in most _Carabi_ L., by means of the notch
and calcar[1638], they are _prehensory_ legs; in _Scarites_ belonging
to that tribe, the Lamellicorn beetles, and the mole-cricket, they
are _fossorious_ legs, or proper for digging[1639]; in _Mantis_,
_Nepa_, and some _Diptera_, they are _raptorious_, or fitted to seize
and dispatch their prey[1640]: they are used also by many insects to
clean their head, eyes, and antennæ, &c. For many of these purposes
they cannot be fit without a structure different from that of the
other legs, which renders it a matter of as great convenience in
descriptions to speak of them and their parts under different names
from those of the legs, as it is of the arms of man; on this account
it is that I propose to give to the fore-leg and its part the names
by which the analogous parts, or what are so esteemed, in the human
species are distinguished;--when spoken of in common with the other
legs, they may still be called the forelegs.

** _Alitruncus._ The alitrunk is the posterior segment of the trunk,
which below bears the four true legs, and above the organs for flight
or their representatives. In treating of this part we may consider
its _insertion_ or _articulation_, its _shape_, _composition_,
_substance_, _motions_, and _organs_.

i. With regard to its _insertion_, or articulation with the manitrunk
and abdomen, it may be observed that it is attached to both by its
whole circumference by means of ligament; in the _Coleoptera_,
_Orthoptera_, and Heteropterous _Hemiptera_ being received by the
posterior cavity of the _prothorax_, the shield of which in these
Orders, especially the last, almost covers and conceals it; but in
the remaining ones it is merely suspended to it. In the former also,
especially in the _Coleoptera_, it seems more separate and distinct
from the manitrunk than from the abdomen, and more independent of its
motions than of those of the latter part: but in the _Hymenoptera_
and _Diptera_ its greatest separation is from the abdomen in both
respects. In many insects, as in the Lamellicorn beetles, the
mole-cricket, &c., the _manitrunk_ terminates posteriorly, drawing
a line from the base of the _prothorax_ to the _antepectus_, in
an oblique section; in other tribes, as in the _Cerambyx_ L., the
Predaceous beetles, &c., the section here is _often_ vertical, but
in the _alitrunk_ the anterior one is _always_ vertical, while the
posterior, by which it articulates with the abdomen, in the Orders
with an ample thoracic shield, is oblique, so that the _pectoral_
portion is more ample than the _dorsal_.

ii. As to its _composition_, the alitrunk is usually much more
complex than the manitrunk; for, besides the instruments of motion,
it consists of numerous pieces. It may be regarded as formed of _two_
greater segments, the first bearing the elytra, or the primary wings,
and the intermediate legs; and the second, the secondary wings and
the hind legs.

1. _Collare_[1641]. The first segment of the alitrunk is the middle
piece of the whole trunk, and therefore, when spoken of _per se_, may
be called the _meditruncus_. It consists primarily of an upper and
lower part, which in the table are denominated the _mesothorax_ and
the _medipectus_. The first piece in the former that requires notice
is the _collar_. I formerly regarded this piece, which is peculiar to
the _Hymenoptera_, _Diptera_, and one tribe of the _Neuroptera_, as the
representative of the _prothorax_ in the other Orders, and this opinion
seems at this time very generally adopted, but subsequent observations
have caused me to entertain considerable doubts of its correctness.
Many other Entomologists have thought it improper to distinguish these
parts by the same name[1642]. Much, however, may be said on both
sides of this question, and I shall now lay before you the principal
arguments that may be adduced in defence of each opinion, beginning
with those that seem to prove that the collar _is_ the analogue of
the _prothorax_. First, then, the collar, like the _prothorax_, is
placed precisely over the _antepectus_, and being placed in the _same_
situation, on that account seems entitled to the _same_ denomination;
especially as in some genera, for instance _Chlorion_ F., it assumes
the very semblance and magnitude of a thoracic shield, and is separated
from the _mesothorax_ by a considerable incisure. Again, in some cases
that have fallen under my own observation, the collar is endued with
some degree of motion distinct from that of the alitrunk, since in
_Pompilus_ and _Chrysis_ the animal can make the former slide over
the latter in a small degree. A third and last argument is, that no
_prophragm_ is formed from the collar: insects that have a thoracic
shield are generally distinguished by having the anterior margin of
the _dorsolum_ deflexed so as to form a _septum_, called in the table
the _prophragm_, which enters the chest and separates the cavity of
the _mesothorax_ from that of the _prothorax_; now in _Hymenoptera_
this septum is a process of the piece behind the collar, and excludes
it from having any share in that cavity. These arguments at first
sight seem to prove satisfactorily the _identity_ of the collar and
_prothorax_. But _audi alteram partem_, and I think you will allow
that the scale containing the claims of the collar to be considered
as a piece _sui generis_, dips much the lowest. And, first, I must
observe, that though in _Hymenoptera_ the collar seems to replace
the _prothorax_ by its situation, yet it is in fact a part of the
alitrunk; for, if the _manitrunk_ be separated from the latter,
the collar remains, in most cases, attached to it[1643], while the
_antepectus_ and arm, with the ligament that covers its cavity above,
the real representative of the prothorax, are easily removed, and this
in recent individuals: as a further proof of this, I must request you
will examine a neuter _Mutilla_; you will see that in this the collar
is not separated from the alitrunk in any respect, but forms one piece
with it, while the _antepectus_ is distinct and capable of separate
motion: further, the action of the collar is upon the alitrunk, it
being of essential importance in flight, whereas the _prothorax_ is
of no other importance than as a counterpoise to that part[1644]. A
further argument to prove the distinction of these parts may be drawn
from the case of _Xylocopa_, a kind of bee. In this genus the collar
forms a complete _annulus_ or segment of the body: now, if it really
represented the prothorax, the under side of the segment, as in those
_Coleoptera_ in which no suture separates the upper from the lower part
of the manitrunk[1645], should represent the _antepectus_, and have
the arms inserted in it; but in the case before us there is a distinct
_antepectus_ bearing the arms received by the socket formed by this
annulus. But the most powerful argument is the fact that some insects
have both the _prothorax_ and _collar_, a circumstance that completely
does away every idea of their identity. If you examine the common
hornet (_Vespa Crabro_), or any saw-fly (_Tenthredo_ L.), you will
find, as was before intimated, that the real covering of the cavity of
the manitrunk is a ligamentous membrane, which properly represents the
_prothorax_. In another genus of the same order (_Xiphydria_ Latr.),
the sides of the _antepectus_ turn upwards and nearly form a horny
covering distinct from the collar[1646], the ligamentous part being
reduced to a very narrow line, and in _Fœnus_ the dorsal fissure is
quite filled up, so that in this the manitrunk is perfectly distinct,
and exhibits both _prothorax_ and _antepectus_ of the usual substance.
In _Nomada_ likewise, _N. Goodeniana_ K. was the species I examined,
there is a short minute _prothorax_ besides the collar. Next let
us turn our attention to the _Diptera_; if you examine the common
crane-fly (_Tipula oleracea_), you will find, first, a regular short
_prothorax_, to which the _antepectus_, with the arms, is attached; and
behind this also is a short collar embracing the alitrunk anteriorly.
The next insects that I shall mention, as exhibiting both _prothorax_
and collar, are the _Libellulina_. These are generally admitted to
have the former of these parts[1647], but besides this they have
also the latter, which is the most ample and conspicuous piece in
the whole trunk[1648]; intervening, as the collar should do, between
the _prothorax_ and those parts of the trunk to which the wings are
attached. There is one circumstance connected with the subject which
should not be overlooked. In the _Hymenoptera_, usually under a
lateral process of the posterior part of the collar, is a spiracle or
respiratory apparatus; in the _Diptera_ there is also one, though not
covered by the part in question, in the same situation; now this you
will find precisely so situated with respect to the second piece in
the thorax of _Tipula oleracea_, proving that this piece is the real
representative of the collar. Enough, I think, has been said to satisfy
you that I have not changed my sentiments on this subject upon slight
grounds. Probably traces of the part in question might be detected
in the thoracic Orders in general, in connexion with some vocal or
respiratory organ[1649]; but having had no opportunity, by an extended
examination of living subjects, to verify or disprove this suspicion,
I shall merely mention it, and conclude this head by observing, that
the collar varies most in the _Hymenoptera_ order, and that its most
remarkable form is in _Vespa_, _Cimbex_, _Dorylus_, &c., in which it
bends into an ample sinus that receives the dorsolum[1650].

2. _Dorsolum_[1651]. Where there is no apparent collar, the
_dorsolum_ (dorslet) is the _first_ piece of the _mesothorax_, and
where there is one, the _second_; it bears the elytra or other
primary organs of flight. It varies in the different Orders,
particularly with respect to its exposure. In Coleopterous insects
it is most commonly, but not invariably[1652], covered entirely by
the shield of the _prothorax_, the _scutellum_ alone being visible;
as it is also in the _Orthoptera_ (with the exception of _Mantis_
and _Phasma_, in the first of which it is partially, and in the
latter intirely exposed), and the Heteropterous, and most of the
Homopterous section of the _Hemiptera_. The scutellum is likewise
covered in _Gerris_, _Hydrometra_, and _Velia_, and the whole of the
back of the alitrunk by a process of the _prothorax_ in _Acrydium_
F., _Centrotus_, &c. But in the remaining Orders, and the tribe of
_Tettigonia_ in the Homopterous _Hemiptera_, the _dorsolum_ is not
hidden by the thoracic shield. It is usually less elevated than the
_scutellum_; in _Necrophorus_, and some other beetles, however,
the latter is most depressed. With regard to its _substance_, it
is generally not so hard and rigid as the _scutellum_, but in
most _Coleoptera_ harder than in the other Orders in which it is
covered; in the _Hemiptera_, except in _Tettigonia_, it approaches
to membrane. As to shape and other circumstances, it varies in the
different Orders. In the beetle tribes it has generally a sinus
taken out of its anterior margin, and it approaches more or less
to a trapezium; in _Blatta_ it is transverse and somewhat arched;
in _Gryllotalpa_ it is nearly square, and distinguished besides on
each side by a minute aperture, fitted with a tense membrane, which
perhaps covers a respiratory apparatus. In the locusts it is more
or less triangular, and in _Mantis_ and _Phasma_ long and slender.
In the _Hemiptera_ the _dorsolum_ appears to consist of several
pieces, variously circumstanced, separated by sutures, corresponding
with which are as many ridges on the inside of the crust[1653].
In the _Libellulina_ it is rhomboidal[1654]; in _Panorpa_ nearly
hexagonal; in the _Ephemerina_ it is ample and oblong; in _Sialis_
and the _Trichoptera_ this part is represented by three subtriangular
pieces, the _scutellum_ constituting a fourth, with the vertices
of the triangles meeting in the centre[1655]; in the _Lepidoptera_
the part in question is large, and receives the _scutellum_ into
its posterior sinus[1656]. The _Hymenoptera_ usually exhibit a very
ample _dorsolum_, mostly subtriangular with the vertex rounded or
truncated, and pointing in some (_Vespa_ L.) to the head[1657], and
in others (_Apis_) to the anus; in the _Diptera_, except in _Tipula_,
the parts of the _mesothorax_ are not separated by any suture, but
only indicated by impressed lines or channels; in the genus last
mentioned, however, the _dorsolum_ is distinct, subrhomboidal, and
received by an angular sinus of the _scutellum_, which last, I think,
is not the part that has usually been regarded as entitled to that
denomination; for this opinion I shall soon assign my reasons.

3. _Scutellum_[1658]. Some writers on the anatomy of insects,
looking, it should seem, only at the _Coleoptera_ and _Orthoptera_,
have regarded the _dorsolum_ and _scutellum_ as forming only one
piece[1659], and others have affirmed that the _Lepidoptera_ and
subsequent Orders have no _scutellum_[1660]. But as we proceed in
considering the _scutellum_ in all the Orders, we shall see that
both these opinions are founded on partial views of the subject, and
that all winged insects have a _scutellum_, more or less distinctly
marked out or separated from the _dorsolum_. In the _Coleoptera_
the _scutellum_ is usually the _visible_, mostly triangular,
piece that intervenes between the elytra at their base[1661], and
which terminates the _dorsolum_. Some Lamellicorn beetles, &c.
(_Scarabæidæ_ MacLeay) are stated not to have the part in question
(_exscutellati_): but this is not strictly correct, for in these
cases the _scutellum_ exists as the point of the _dorsolum_ covered
by the _prothorax_, though it does not intervene between the elytra:
in others of this tribe, as _Cetonia chinensis_, _bajula_, &c.,
it separates these organs at their base, though it is covered by
the posterior lobe of the _prothorax_: in _Meloe_ F., the elytra
of which are immoveable, there seems really to be no _scutellum_.
Generally speaking, as was lately observed, but not always, it is
distinguished from the _dorsolum_ by being more elevated: this is
particularly conspicuous in the genus _Elater_, in which it is a
flat plate elevated from the _dorsolum_ by a pedicle; in _Sagra_ the
latter part is horizontal, while the _scutellum_ is vertical: and
even in cases where the distinction is not so striking, these parts
are separated either by a line, or some difference in their sculpture
and substance. In this Order this part varies greatly, and often in
the same tribe or genus, both in size and shape; being sometimes very
large[1662], and sometimes very minute; sometimes very long, and
sometimes very short; sometimes nearly round, at others square; now
oval or ovate, heart-shaped, triangular, acuminate, intire, bifid,
&c. In the _Orthoptera_, though less conspicuous, it still is present
as a triangular elevation of the middle of the posterior part of
the dorsolum, with the vertex either pointing towards the head, as
in _Blatta_, or towards the tail, as in _Locusta_ Leach[1663]. In
the Heteropterous section of the _Hemiptera_ (which, in columns of
_Mandibulata_ and _Haustellata_, appear to bear the same reference
to the _Coleoptera_, that the _Hymenoptera_ do to the _Diptera_,
and the Homopterous _Hemiptera_ to the _Orthoptera_[1664]) the part
we are considering is mostly very large and conspicuous, quite
distinct from the _dorsolum_, and in some (_Tetyra_ F.) covering
the whole abdomen, as well as the _Hemelytra_ and the wings; it is
most commonly, as in the _Coleoptera_, obtriangular[1665], but in
the last-mentioned genus it often approaches to a pentagonal shape.
Though usually so striking a feature in this tribe, in the aquatic
bugs (_Gerris_ &c.) it is covered by the _prothorax_. In some
species of _Reduvius_ F. (_R. biguttatus_, _mutillarius_, _lugens_,
&c.) it is armed with one or more dorsal or terminal spines. In the
Homopterous section, where the _dorsolum_, as in _Tettigonia_ F., is
not covered by the _prothorax_, the _scutellum_, which is merely a
continuation of that part, bears some resemblance to a St. Andrew's
cross, and terminates in a fork[1666]; in _Fulgora_, in which it is
partly covered, it is merely the triangular point of the _dorsolum_:
in the _Cercopidæ_, &c., whose _dorsolum_ is wholly covered, the
triangular scutellum is distinct from it; in _Centrotus_, _Darnis_,
and _Membracis_, in which the _prothorax_ is producted, and covers
the abdomen more or less, the _scutellum_ is a short transverse
distinct piece. In the _Lepidoptera_, from the difficulty of abrading
sufficiently the scales and hairs without injury, it is difficult
to obtain a correct idea of the part in question; in the cabbage
butterfly (_Pieris Brassicæ_) it appears to be triangular: in the
humming-bird hawk-moth (_Macro-glossum Stellatarum_) it approaches
to a rhomboidal shape[1667]; and in the eggar-moth (_Lasiocampa
Quercus_) it is completely rhomboidal. In the _Libellulina_, in the
_Neuroptera_ Order, it seems to be represented by the posterior
point of the _dorsolum_, which terminates in something like a St.
Andrew's cross[1668]. In most of the other tribes of this Order the
_scutellum_ is a triangular piece, with the vertex to the head,
received between two pieces of the dorsolum; in _Psocus_ it is nearly
like that of _Tettigonia_ before described. In the _Hymenoptera_
the _scutellum_ is separated from the _dorsolum_, which it often
embraces posteriorly, as the collar does in front, by a suture; it
varies occasionally in shape in the different tribes, most commonly
it is crescent-shaped, but in many _Ichneumonidæ_ and others it is
triangular[1669]; in the hive bee, &c., it overhangs the succeeding
piece of the alitrunk; in _Melecta_, _Crocisa_, &c., it is armed
with a pair of sharp teeth[1670]; in others (_Oxybelus uniglumis_,
&c.) with one or more spines, and in some with a pair of long
horns[1671]. Before I describe this part in the _Diptera_, it will
be proper to assign my reasons for considering a different piece as
its representative, from what has usually been regarded as such, and
which at first sight seems the analogue of what I admit to be the
_scutellum_ in the _Hymenoptera_. The _dorsolum_, and its concomitant
the _scutellum_, belong to the first pair of the organs of flight,
which are planted usually under the sides of the former, and in the
case of _wings_, by their Anal Area, connected either mediately or
immediately with the latter. Now, if you trace the sides of the piece
that I have considered as the part in question in _Hymenoptera_,
you will find that they lead you not to the base of the _lower_
but to that of the upper _wings_[1672], and in the saw-flies
(_Tenthredo_ L.) you will see clearly that the Anal Area of these
wings is attached to a process of it, a proof that it belongs to
the _mesothorax_, or region of that pair. But in the _Diptera_, the
part that has been usually called the _scutellum_ is not at all
connected, either by situation or as a point of attachment, with
the wing itself, but with the lower valve of the _alula_, which is
with reason thought to be the representative of the secondary wing
of the tetrapterous Orders. You may see this even in the common
crane-fly (_Tipula_), in which there is a real _alula_, connected
by means of a lateral process, terminating in ligament, with this
supposed _scutellum_. If you examine further the same insect, you
will easily find what I regard as the true one in the bilobed piece
which receives the _dorsolum_, situated between the wings, and to
the sides of which they are attached. In _Asilus_, _Tabanus_, &c.,
this part is transverse, and only distinguished on each side by an
oblique impressed line; in the _Muscidæ_ it is square, and marked by
a straight transverse one.

4. _Frænum_[1673]. This appendage to the _scutellum_ and _dorsolum_
varies considerably in the different Orders, and in many cases, as
you will see, is a very important part, being the process by which
the former is mostly connected with the elytra or upper wings. In the
_Coleoptera_, the elytra of which are nearly stationary in flight, and
therefore less require any counteraction to prevent their dislocation,
this part is commonly merely a process or incrassation of the under
margin of the scutellum, which towards the base of the _dorsolum_ is
dilated to form the socket for the elytra. Its use as a countercheck
in this Order is best exemplified in the common water-beetle (_Dytiscus
marginalis_). This at the inner base of the elytra has a membranous
fringed _alula_ resembling those of _Diptera_; to the lower fold of
this the extremity of the _frænum_ is attached, which forms a right
angle with the scutellum, and the upper fold is attached to the base
of the elytrum[1674]. The object of this appendage is probably to
prevent the dislocation of these organs, which seems to indicate that
they are used more in flight than those of other beetles. The _Blattæ_
also, in the next Order, have a winglet attached to the anal area of
the _tegmina_. The _frænum_, as in the preceding Order, lies under the
margin of the _scutellum_ and _dorsolum_, but which here forms one
uninterrupted transverse line; it is nearly vertical, and is attached
to the _alula_. The structure is not very different in the other
_Orthoptera_[1675], but the _frænum_ is surmounted or strengthened
by one or two ridges; in _Mantis_ it runs from the scutellum in an
angular or zigzag direction--but in all it is attached immediately to
the _tegmen_. In the Heteropterous _Hemiptera_ it is represented by the
narrow bead adjacent to the scutellum on each side[1676], which dilates
into a flat plate as it approaches the _Hemelytrum_, with the Anal Area
of which it is connected. But the Homopterous section of the Order in
question furnishes examples of the most remarkable structure of this
countercheck, which proves that it is really, what its name imports, a
_bridle_. If you examine the great lanthorn-fly (_Fulgora laternaria_),
or any species of _Tettigonia_, &c., you will find adjacent to the
scutellum or parallel with it, on each side a flat plate; and
from the angle of that part in the first case, and from one of its
processes in the last, you will further perceive a ridge or nervure
which runs along this plate, in one forming an angle, and in the other
being nearly straight, to the base of the _tegmen_, where it becomes
a marginal nervure to a membrane that is attached to the posterior
part of the base of the Anal and Costal Areas; and that this marginal
nervure, like a _trachea_, consists of a spiral thread, or rather of
a number of cartilaginous rings connected by elastic membrane[1677],
and consequently is capable of considerable tension and relaxation,
as the _tegmen_ rises and falls in flight. In the _Lepidoptera_ it
appears to be a short piece overhung by the scutellum, which as it
approaches the base of the wing is dilated. In the _Libellulina_,
to go to the _Neuroptera_, it has the same kind of elastic nervure
connected with the Anal Area of the wing which I have just described
in the Homopterous _Hemiptera_; another nervure, in _Æshna_ at least,
appears to diverge upwards from the scutellar angle to the Intermediate
Area[1678]: a structure little different distinguishes the rest of the
_Neuroptera_, and even the _Trichoptera_. In the _Hymenoptera_ this
part varies somewhat; in the majority perhaps of the Order, as well
as in the _Diptera_, it appears to be merely the lateral termination
of the scutellum where it joins the wing; but in some tribes, as
in _Tenthredo_ L. (especially _Perga_ Leach), _Sirex_ L., and the
_Ichneumonidæ_, a ridge, and sometimes two, runs from the scutellum to
the wing; the upper one, where there are two, as in _Perga_, being the
stoutest, and connecting with the _Costal_ Area, and the lower one with
the _Anal_.

5. _Pnystega_[1679]. We learn from M. Chabrier, that in the common
dragon-fly, a space, consisting of three triangles, which immediately
succeeds the _frænum_, affords attachment to no muscles, but merely
covers aërial vesicles[1680]. This is the part I have called the
_pnystega_[1681]. An analogous piece may be discovered in _Phasma_
and _Mantis_ in a similar situation; but I cannot trace it in
_Locusta_ Leach, or in the other Orders.

Having considered the parts that constitute the _mesothorax_, we will
next say something upon those, as far as they require notice, that
compose the _medipectus_ or mid-breast. But first I must observe,
in general of the _medipectus_ and _postpectus_ taken together, or
the whole underside of the _alitrunk_, that though usually they
are in the same level with the _antepectus_ or under side of the
_manitrunk_, yet in several instances, as the _Scarabæidæ_ MacLeay,
the _Staphylinidæ_, &c. they are much more elevated than that part;
they are also usually longer, very remarkably so in _Atractocerus_,
but in _Elater sulcatus_ and many others they are shorter. These
parts are also commonly rather more elevated than the abdomen,--much
so in some, as _Molorchus_; but scarcely at all in others, as
_Buprestis_, the Heteropterous _Hemiptera_, &c. In some of the
latter (_Tetyra_ F.) the abdomen seems the most prominent. Another
observation relating to this part must not be omitted, namely, that
though in many cases the _medipectus_ and _postpectus_ are perfectly
distinct and may be separated, yet in others, as for instance the
Lamellicorn beetles, the _Hymenoptera_ and _Diptera_, &c., no suture
separates them; so that though the upper parts, the _mesothorax_ and
_metathorax_, are separable, the lower ones just named are not so.

6. _Peristethium_[1682]. The first piece of the _medipectus_ is
what I have called, after Knoch, the _peristethium_[1683]. This
immediately follows the _antepectus_; on each side it is limited by
the scapulars, and behind by the mid-legs and _mesosternum_. Its
antagonist above is usually the _dorsolum_. In the _Coleoptera_ Order
it varies occasionally, both in form and magnitude, but not so as
to merit particular notice, except that both are regulated by the
scapulars--if these are small, the _peristethium_ is ample; and,
_vice versa_, if they are large it is small. In all the following
Orders, except the _Hymenoptera_, it is equally inconspicuous, but
in them it is often more remarkable. I have a Brazilian species of
_Cimbex_ (_C. mammifera_ K. MS.) which appears undescribed, in which
this part swells into two breast-like protuberances, terminating
posteriorly in membrane, as if it had separate motion: in the
golden-wasps (_Chrysis_ L.) it is anteriorly concave to receive the
_coxæ_ of the mid-legs; and in _Stilbum_, of the same tribe, it is
armed with one or more conical obtuse teeth.

7. _Scapularia_[1684]. The scapulars are situated between the _coxæ_
of the mid-legs and the base or axis of the upper organs of flight,
and they seem to act as a fulcrum to each. In the _Coleoptera_ Order
they are most commonly quadrangular or subquadrangular, often divided
diagonally, and sometimes transversely, by an impressed line; the
posterior part, which is usually the most elevated and often has an
uneven angular surface, is that which intervenes between the coxæ and
elytra: where the former are short, as in the Capricorn beetles, the
scapulars are long; and where they are long, as in the Petalocerous
ones, the latter are short. The anterior part is that which forms
the lateral limit of the _peristethium_, upon which it often
encroaches: this part, in conjunction with the _dorsolum_ above, and
the last-named part below, forms the kind of _rotula_ that plays in
the posterior _acetabulum_ of the manitrunk, as the head does in the
anterior one. In the flower-chafers (_Cetonia_ F.) the scapulars are
very thick and elevated, and interpose between the posterior angles
of the _prothorax_ and the shoulders of the _elytra_, which is one
of the distinguishing characters of that tribe: in this case the
lower angle of the scapular connects with the _coxa_ of the mid-leg,
and the upper angle with the axis of the _elytra_; and the most
elevated and thickest part of the scapular is about midway between
the two. This robust structure seems to indicate that the scapular
has to counteract a powerful action both of the leg and elytrum.
In the _Orthoptera_ the scapulars are usually divided into two
parallel pieces, corresponding probably, though more distinct, with
the two parts lately noticed of those of the _Coleoptera_: the upper
side of the socket of the mid-leg is common to the base of _both_
these pieces, but the articulation of the _tegmen_ is chiefly with
the _anterior_ one. In the grasshoppers, locusts, &c. (_Gryllus_
L.) in which tribe this leg is nearly _opposite_ to that part,
the scapular inclines but little from a vertical position[1685];
but in the praying-insects (_Mantis_), spectres (_Phasma_), and
cockroaches (_Blatta_), in which the insertion of the mid-legs is
_behind_ that of the _tegmina_, it is nearly horizontal. In the
Heteropterous _Hemiptera_ the anterior part of the scapular is
covered by the _antepectus_, and separated by a ridge, more or
less pronounced, from the open part; the whole is of an irregular
shape, and nearly parallel with the _parapleura_. In the Homopterous
section it likewise consists of two pieces, and sometimes of more.
Thus in _Tettigonia_ F. it is bilobed, and between it and the coxa
two small pieces are inserted[1686]. In some others, _Iassus Lanio_
F., &c., it is not very unlike the scapular in _Coleoptera_, being
subquadrangular and divided diagonally. In the _Neuroptera_ this
part and the _parapleura_ are parallel, and placed obliquely[1687].
In the common dragon-fly (_Æshna viatica_) the former forms nearly a
parallelogram[1688], which is not divided by any ridge or channel,
but its lower half is separated into two unequal parts by a black
longitudinal line, opposed to which on the inside is a ridge. The
mid-leg in these is connected with the scapular by the intervention
of a triangular transverse anterior piece, which in fact seems
only marked by a black channel, to which also interiorly a ridge is
opposed[1689]. In the rest of the Order it is divided longitudinally
into _two_ parallel pieces. In _Panorpa_ the posterior piece is
longer than the anterior and props the coxa behind; in _Myrmeleon_
and _Perla_, &c., it appears to consist of _three_ pieces. I have
not been able to obtain a clear idea of them in the _Lepidoptera_,
except that they have more than one piece. _Hymenopterous_ and
_Dipterous_ insects for the most part have no scapular distinct from
the _peristethium_; but in _Cimbex_, _Perga_, and other saw-flies, it
seems represented by its posterior depressed and sometimes membranous
part: in _Vespa_, &c. a small subtriangular piece, just below the
base of the upper wing, is probably its analogue[1690].

8. _Mesosternum_[1691]. The central part of the _medipectus_, or
that which passes between the mid-legs when elevated, protended, or
otherwise remarkable, is called the _mesosternum_ or mid-breast-bone.
In the _Coleoptera_ Order it exhibits the most numerous variations, and
is usually the most strongly marked of any of the three portions of the
_sternum_, affording often important characters for the discrimination
of genera and subgenera. It may be said to be formed upon three
principal types--the first is, where it is a process of the posterior
part of the _peristethium_, and points towards the anus or the
head;--the second, where it is a process of the anterior part of the
_mesostethium_, and points only towards the head: in this case there
is no suture to separate the _medipectus_ from the _postpectus_;--the
last type is where it is a ridge formed by a process both of the
_peristethium_ and _mesostethium_ meeting between the legs; an example
of this you will see in the common dung-chafer (_Geotrupes_ Latr.).
Upon the two first of these cases I shall offer a few remarks;--the
last affording no variation need only be mentioned.

If you examine the terrestrial Predaceous beetles (_Cicindela_ and
_Carabus_ L.) you will find that the _peristethium_ is usually flat,
terminating towards the _postpectus_ in a kind of fork, the sinus
of which receives the anterior point of the _mesostethium_--this
is the _mesosternum_; but in the aquatic insects of this tribe, at
least in _Dytiscus marginalis_, &c. the structure at first sight
seems different, for _apparently_ the _prosternum_ is received by the
anterior fork of the _mesostethium_; but if you proceed to separate the
manitrunk from the alitrunk, you will find that the true _mesosternum_
of the usual form is quite covered by this point, which curves towards
the breast, is longitudinally concave to receive the point of the
_prosternum_, and permit its motion in the groove. In some Heteromerous
beetles, as the _Helopidæ_, &c. this part is anteriorly bilobed, so
as to form a cavity which receives the point of the _prosternum_ when
the head is bent down: in _Helops nitens_ (_Tenebrio_ Oliv.) this
sinus represents a crescent; in _Cistela Ceramboides_ it is shaped
like the Greek letter γ; in the Lady-bird (_Coccinella_ L.) it assumes
nearly the shape of a Saint Andrew's cross; in _Spheniscus_ K.[1692]
the _mesosternum_ is wide, concave and wrinkled, with an anterior and
posterior sinus; while in the analogous genus _Erotylus_[1693] it is
convex anteriorly, and posteriorly more or less rounded; in _Doryphora_
it is a long, robust, subconical horn, often standing at an angle of
about 45°, overhanging the _prosternum_.

In the genus last named, though its _mesosternum_ in its direction
and appearance resembles that of many Petalocerous beetles, yet it is
separated by an evident suture from the _mesostethium_; but in the
last-mentioned tribe its representative is a process of the latter
part: yet as the _peristethium_ and _mesostethium_ are separated by
no suture, though in some cases a transverse channel, and in others
merely a coloured line, marks the point where they may be considered
as soldered together, in these cases the _mesosternum_ may perhaps
be said to be common to both. In this great family, which includes
within its limits some of the most singular and wonderful in their
structure and armour, as well as some of the most brilliant and
beautiful of the beetle tribes,--the part in question, in a vast
number of cases, will enable the Entomologist satisfactorily to
trace its numerous groups, not only where it rises or stretches
out into a horn or ridge, but even often where it is merely a flat
space between the mid-legs. I shall notice some of its most striking
variations in this tribe. In _Phanæus festivus_, and in _Macraspis_
and _Chasmodia_ MacLeay, it is elongated horizontally, with the apex
curving upwards; in _Anoplognathus_ it is horizontal, straight, and
figures an isosceles triangle; in _Cetonia suturalis_, _vitticollis_,
&c. it is very long, passing between the arms and nearly reaching
the head; in _C. marmorea_, _Lanius_, &c. it is a lofty, robust,
conical prominence; and in many _Rutelidæ_, especially those with
striated elytra, it is pyramidal or four-sided; it varies also in its
_termination_, particularly in the _Cetoniadæ_; and even where there
is little or no elevation of it, as in the _Scarabæidæ_ MacLeay, it
is often terminated anteriorly by lines that vary in their angle or
curvature. The genus _Copris_, as restricted by Mr. W. S. MacLeay,
may from an inspection of this circumstance be divided into several
families. Thus in _C. Molossus_ and affinities its _termination_
represents the letter ⅄ reversed, or a triangle surmounted by a
mucro; in _C. orientalis_, &c., it ends in an acute-angled triangle;
in _C. lunaris_, &c. in an obtuse-angled one; and in _C. Iacchus_,
&c., in the segment of a circle.

The part we are considering is not so important in the other Orders.
In the _Orthoptera_, however, it is occasionally remarkable. In
_Acrida viridissima_ (_Locusta_ F.) attached to the anterior margin
of the _peristethium_ are two long triangular pieces which appear to
represent this part; in the kindred subgenus, _Conocephalus_[1694],
it is a single piece bifid at the apex; in _Gryllotalpa_ it is a very
elevated hairy ridge; and in _Locusta_ Leach, it is a flat anterior
process of the _mesostethium_. In the Heteropterous _Hemiptera_ this
part is often merely a portion of the channel in which the _promuscis_
reposes; but sometimes, as in _Edessa_ F., it is an elevated piece
varying in its termination. In the remaining Orders, as far as I have
had an opportunity to examine them, it can scarcely be said to exist
separately from the _medipectus_, except that in _Tipula_ Latr. a
bipartite subtriangular membranous piece seems to be its analogue.

We are now to consider the last segment of the alitrunk, which, as a
whole, may be denominated the _potruncus_; it bears the second pair
of the organs of flight, and the last pair of legs. The upper side of
this is the _metathorax_, and its lower side the _postpectus_.

9. _Postdorsolum_[1695]. The first external piece of the _metathorax_
is the _postdorsolum_, which presents itself under very different forms
and circumstances in the different Orders. In the _Coleoptera_ it is
intirely covered by the _dorsolum_ and _scutellum_; it is generally
more or less of a membranous substance, or partly membranous and partly
corneous, which enables it to yield more to the action of the wings in
flight; it is usually an ample transverse piece with tumid sides[1696];
but in the _Scarabæidæ_ MacLeay, it is short though very wide; and
in _Cychrus_, and probably other _apterous_ beetles, it is extremely
minute and almost obsolete. In the _Orthoptera_ Order, I observe once
for all, the part in question, as well as the _postscutellum_ and
_postfrænum_ are mere counterparts of the _dorsolum_, _scutellum_,
and _frænum_, except that in some cases they are larger[1697]. In the
Heteropterous _Hemiptera_ at first sight it would appear that all
the parts of the _metathorax_ were altogether wanting or absorbed
in the ample _scutellum_; but if you remove this with care, you
will find _under_ it their representatives, its lower surface being
hollowed out to receive them. The _postdorsolum_ appears in these as
a transverse obtusangular band; in the _Nepidæ_, _Notonectidæ_, &c.
the three parts of the _metathorax_ seem united into a single plate,
emerging laterally from under the _scutellum_ below the _frænum_;
in which, however, some traces of a distinction between them may be
discovered. In the Homopterous section the _Fulgoridæ_ exhibit these
pieces very distinctly, covered only at the base by the _mesothorax_:
but in _Tettigonia_ they are not so easily detected; they exist
however as a narrow strip or band, almost concealed by that part.
As to the _Lepidoptera_ Order, in _Pieris Brassicæ_ at least, the
_postdorsolum_ is represented by a pair of nearly equilateral triangles
whose vertexes meet in the centre of the _metathorax_, and between
which and the _scutellum_ is a deep cavity; but in _Macroglossum
Stellatarum_ and _Lasiocampa Quercus_, there appears to be also a
central transverse piece between them. In the _Neuroptera_ there is no
material or striking difference between the parts of the _mesothorax_
and _metathorax_[1698]. In the _Hymenoptera_ more variety occurs in
this part. In the saw-flies, &c. (_Tenthredo_ L.) the _postdorsolum_ is
a transverse piece covered by the _scutellum_; in the _Ichneumonidæ_
it is smaller, but not covered; in the _Vespidæ_ it is apparent,
transverse, and with the _postscutellum_ obtusangular[1699]; in
_Apis_ it is overhung by the _scutellum_. The _Diptera_ exhibit some
variations in this part. In _Tipula_ it consists of three pieces placed
transversely, the central one quadrangular, and the lateral ones
roundish; in the _Asilidæ_ and most others of this Order, with the
_postscutellum_, it forms a segment of a circle[1700], sometimes armed
with a pair of spines, as in _Stratyomis_ F., and is what has been
usually regarded as the real _scutellum_, though, as I have endeavoured
to show, not correctly[1701].

10. _Postscutellum_[1702]. The _postscutellum_ bears the same relation
to the _postdorsolum_ that the _scutellum_ does to the _dorsolum_,
but it is seldom, if ever, a distinct piece. In the _Coleoptera_ it
is represented by the longitudinal narrow channel that terminates
the _postdorsolum_ towards the anus[1703]: this usually figures an
isosceles triangle with the vertex truncated or open; but in _Copris_
the triangle is equilateral. In the other Orders it is little more than
the central posterior point of the _postdorsolum_[1704].

11. _Postfrænum_[1705]. The part now mentioned is much more important
than the preceding one, and must not be passed over so cursorily. In
the _Coleoptera_ it usually presents itself under the form of two
large and usually rather square panels, the disk of which is convex,
but the rest of their surface unequal, which are situated one on each
side of the postscutellum[1706]; under the anterior outer angle of
these is the socket or principal attachment of the secondary wings,
and their basal margin is attached to their outer side; posteriorly
behind the vertex of the _postscutellum_ the _postfrænum_ is crowned
with a ridge or bead, below which it descends vertically or obliquely
to the abdomen; this ridge often turns upwards, and proceeds towards
the middle of the basal margin of the wing. In the Petalocerous
beetles the part in question is usually more or less hairy; but in
many others, as the rose-scented Capricorn (_Callichroma moschatum_),
&c. it is naked. At its side you will commonly observe several plates
and tendons (_osselets_ Chabr.) connected _inter se_ and with the base
of the wing by elastic ligaments, which are calculated to facilitate
the play of those organs. In the _Orthoptera_, _Neuroptera_, and
Homopterous _Hemiptera_, the _postfrænum_ does not differ materially
from the _frænum_[1707]. In the Heteropterous section of the last Order
it is usually a transverse ridge terminating the _postdorsolum_, with
a bifurcation where it unites with the wing; but in _Tetyra_ F. (at
least so it is in _Tetyra signata_,) it is a nearly vertical piece,
marked in the centre with an infinity of very minute folds, which
probably by their alternate tension and relaxation let out and pull
in the wings. Amongst the _Lepidoptera_ it is not remarkable. In the
_Hymenoptera_ Order it is mostly represented, I think, by a double
ridge or fork, sometimes however obsolete, but very conspicuous in the
saw-flies, which laterally terminates the _postdorsolum_; the upper
branch, usually the thickest, going to the anterior part of the base
of the underwing, and the lower one to the posterior. You may observe
something similar in the crane-flies (_Tipula_ Latr.) and _Asilidæ_. A
tendon proceeding from the point of the _postscutellum_ forms a fork
near its end, the upper branch of which connects with the anterior and
the lower with the posterior valve of the winglet; the structure is a
little, but not essentially, different in other _Diptera_.

12. _Pleura_[1708]. By this name I would distinguish the part which
laterally connects the _metathorax_ and _postpectus_. It includes in
it the socket of the secondary wings. In the _Coleoptera_ this is a
two-sided piece lying between the _postfrænum_ and the _parapleura_,
with the upper side horizontal and the lower vertical[1709]--a tendon
usually proceeds from its anterior extremity to the base of the wing.
In the _Orthoptera_, _Neuroptera_, and other Orders, it is merely
the longitudinal line of attachment of that part; but in the genus
_Belostoma_ Latreille, related to the water-scorpion, it presents a
peculiar structure, being a deep channel or demitube, filled at its
posterior extremity by a spiracle and its appendages[1710].

13. _Metapnystega_[1711]. This part, although in the table I have
placed it as an appendage of the _pleuræ_, is not always confined
to them, as you will soon see. It either covers aërial vesicles, or
is the seat of a spiracle. In the Order _Coleoptera_ it is of the
former description. If you examine the _metathorax_ of the common
dung-chafer (_Geotrupes stercorarius_), in the horizontal part of
the _pleura_ you will see a sublanceolate or subelliptical rather
membranous silky tense plate, with its point towards the head,--this
is the part we are considering; something similar you will find in
most beetles; but in some, as _Callichroma moschatum_, it is less
conspicuous. This part, as far as I have observed, is not so situated
in any other Order, except in some Heteropterous _Hemiptera_: in
_Belostoma_ the channel lately mentioned is filled up at its posterior
end by a red organ with an anterior vertical fissure, terminating
behind in a conical bag: in _Notonecta_ the _pleura_ has something of
a plate like that of _Coleoptera_, but of a horny substance. In the
_Orthoptera_ and _Neuroptera_ this part changes its situation, if it
be indeed synonymous; and as the _pnystega_ follows the _frænum_, so
the _metapnystega_ succeeds the _postfrænum_. In the _Libellulina_
M. Chabrier found that this as well as the other covered aërial
vesicles[1712], and it probably does the same in the other cases in
which it occurs. In _Mantis_ and _Phasma_ in the _Orthoptera_ it is
very minute; but in _Locusta_ Leach, it is more conspicuous under the
form of a tense membrane, the surface of which is depressed below that
of the abdomen: in _Acrida viridissima_ K. it fills the sinus of the
_postfrænum_, and is vertical, as it is in _Æshna_. It is worthy of
remark that this piece bears some analogy to that below the ridge of
the part just named in _Coleoptera_, which descends either vertically
or obliquely to the abdomen[1713]. A similar space, though often nearly
obsolete, may be seen in the _Hemiptera_ and _Lepidoptera_. But the
Orders in which this part is most conspicuous are the _Hymenoptera_
and _Diptera_, and in these its aërial vessels are connected with
a spiracle. In _Tenthredo_ L. and _Sirex_ L., what Linné named
_grana_, from their situation, should be regarded as belonging to
the _pnystega_, and whether there is any part representing the
_metapnystega_ I am not quite satisfied; perhaps the membrane at the
base of the abdomen in _Tenthredo_, and the bipartite piece, apparently
its first segment, in _Sirex_[1714], may be its analogues: but in the
great majority of the Order, the convex or flat piece that intervenes
between the _postdorsolum_ and its adjuncts and the abdomen, and which
bears a spiracle on each side, is the _metapnystega_[1715]. This part
is often remarkable, not only for its size, but for the elevated ridges
that traverse it, as in _Ichneumon_, _Chlorion_, &c. In the last genus
it is of a pyramidal shape, with the anterior part horizontal and the
posterior vertical; it is altogether vertical in _Vespa_, _Apis_,
&c. Amongst the _Diptera_, in _Tipula_ it is nearly horizontal, and
shaped like a cushion; but in general in this Order it is vertical, and
concealed under the _postdorsolum_[1716].

We are now to consider the parts that constitute the _postpectus_ or
under-side of the _metathorax_, and which bears the posterior pair of
legs.

14. _Mesostethium_[1717]. This part in _Coleoptera_ is terminated
anteriorly by the _peristethium_, _scapulars_, and _mesosternum_,
laterally by the _parapleuræ_[1718], and behind by the coxæ of the
posterior legs[1719], which generally are inserted transversely between
it and the abdomen. It is commonly very wide; but in _Dytiscus_ L.,
_Carabus_ L., &c., in which the _coxæ_ and _parapleuræ_ are dilated, it
is proportionally reduced: its length is regulated by the distance of
the intermediate and posterior legs; where these are far asunder, as in
the rose-scented Capricorn (_Callichroma moschatum_), &c. it is long:
but where they are near each other, as in the _Scarabæidæ_ MacLeay, it
is short; its width, however, generally exceeds its length. In shape
it is generally subquadrangular[1720], though sometimes rhomboidal,
and other forms of it occur. Between the hind-legs it generally
terminates in a notch or bifurcation distinct from the _metasternum_,
as in _Hydrophilus_, &c.; in _Hister_ there is no notch, and in
many _Scarabæidæ_ it projects between the hind-legs in a truncated
or rounded mucro; in the Vesicatory beetles, _Meloe_ L., it is more
elevated than the _medipectus_, towards which it descends almost
vertically; in _Dytiscus_ L., _Carabus_ L., &c., this part is usually
divided into two by a _transverse_ sinuous channel, and in _Elater_
by a _longitudinal_ straight one. In many _Orthopterous_ genera,
_Gryllotalpa_, _Acrida_ K., _Locusta_ Leach, &c., the _mesostethium_
consists of _two_ pieces[1721]. It is remarkable that in many of these
genera, in this part, as likewise in the _medipectus_ and _antepectus_,
are one or more perforations which appear to enter the chest, the use
of which I shall explain hereafter. In the _Libellulina_, as I shall
soon have occasion to shew, there is a peculiar arrangement of the
legs and wings, in consequence of which this part is placed behind the
posterior ones. In the remaining Orders, the _mesostethium_, though it
exists, exhibits no peculiarities worthy of particular notice, except
in some _Aptera_ and _Arachnida_: thus, in _Nirmus Anseris_ it is
terminated posteriorly by a pair of transverse membranous appendages
which cover the base of the posterior _coxæ_; in _Scorpio_ it consists
of two pieces, the _pectines_[1722] being attached to the sides of the
posterior one.

15. _Parapleura_[1723]. The _parapleura_, speaking generally, is
that piece of the _postpectus_ which, intervening between the
_pleura_, _mesostethium_, and _scapulars_, is attached by its
posterior extremity to the _coxæ_ of the hind-legs; by means of
the _pleura_, from which it does not appear to be separated by any
suture, it connects the secondary or under-wings with the hind-legs,
as the scapular does the primary ones with the mid-legs; so that the
direction of the _parapleura_ depends upon the relative situation
of the legs and wings. In Coleopterous insects its direction is
_horizontal_, it being generally a narrow subquadrangular piece that
runs straight from the posterior coxæ to the scapular[1724], and
usually divided into two unequal portions by an elevated or impressed
line. In the palm-weevil (_Calandra Palmarum_) this part is wider
than usual; in _Dytiscus marginalis_,--in which genus, as likewise
in _Carabus_ L., the _coxæ_ are incapable of separate motion,--it is
nearly a right-angled triangle, and is divided longitudinally into
two _unequal_ portions. In the _Orthoptera_ Order this part usually
consists of two _equal_ portions, and its direction is sometimes
nearly horizontal, as in _Mantis_ and _Phasma_; sometimes forming
an angle with the horizon, as in _Blatta_; and sometimes nearly
vertical, as in _Locusta_ Leach. In the two first cases the wings
are _before_ the legs, and in the last their position is _over_
them. In the Heteropterous _Hemiptera_ it is parallel with the
scapular, is divided into two unequal portions, and its direction is
more or less inclined to the horizon[1725]. As to the _Homopterous_
section--in _Fulgora_ it is of a very irregular shape with an
angular surface, and its direction from the leg to the wing is first
nearly vertical and then horizontal: in _Tettigonia_ it is almost
vertical, and consists of two nearly equal portions. To come to the
_Neuroptera_--in the _Libellulina_ it consists of two pieces, like
those of the scapulars, but smaller[1726], and its inclination is
towards the head: in _Panorpa_ also it resembles the scapulars both
in form and other circumstances[1727]. In the remaining Orders it
exhibits no very remarkable features.

16. _Metasternum_[1727]. The central part of the _mesostethium_
when elevated or porrected, or otherwise remarkable, is called the
_metasternum_. In the _Coleoptera_, in those cases, as we have seen
above[1728], in which the _medipectus_ and _postpectus_ form one piece,
its anterior point becomes the _mesosternum_; but in others, as the
Predaceous and Capricorn-beetles, &c., it is received in a sinus or
fork of that part, or meets it. It is usually neither so remarkable nor
important as the _mesosternum_. In _Bolbocerus_ K. it is a rhomboidal
elevation: in _Gyrinus_ a ridge; as also in many _Hydrophili_, in
which it passes between the hind-legs to the abdomen, and terminates
in a sharp point[1729]; and in _Dytiscus_ its two diverging lobes
cover the base of the posterior trochanters[1730]. In the _Orthoptera_
Order this part is not remarkable; but in _Acrida viridissima_ K. it
consists of three triangular pieces, the lateral ones being erect,
and the intermediate one horizontal: in _Locusta_ Leach it resembles
the _mesosternum_[1731]. In the Heteropterous _Hemiptera_ the whole
_mesostethium_ is elevated, and terminates at both ends in a fork,
the anterior one receiving the point of the _promuscis_, and the
posterior one that of the _epigastrium_: in the Homopterous section,
the _Tettigoniæ_ F. have usually a distinct metasternal point between
their hind-legs. In the remaining Orders there is no _metasternum_,
or no remarkable one, except in one singular Hymenopterous genus,
_Evania_, the parasite of the _Blattæ_[1732], in which there is a
forked posterior process of the _mesostethium_ with recurved points.

17. _Opercula_[1733]. By this term I distinguish those plates, before
largely described[1734], which cover the drums of male _Tettigoniæ_ F.;
and likewise those called also by the same name by M. Chabrier[1735],
which cover, in many cases, the _vocal apparatus_ of the trunk of
insects: those of _Melolontha vulgaris_ he describes as situated below
the wings, and between the two segments of the _alitrunk_[1736]; and
if you take this insect and remove the elytra, the _mesothorax_ and
scapulars, under the latter and below the wing you will find an oval
convex plate, which is probably the part he is speaking of;--but it is
better exemplified, I think, in the common _Dytiscus marginalis_, in
which it is very distinct as a convex subtriangular plate connected
with the _metathorax_ by membranous ligament, covering a kind of pouch,
and appearing to open and shut at the vertex[1737].

I must here observe, with regard to the _Aptera_ and _Arachnida_,
that the trunk in them is much more simple than in those insects that
are furnished with _wings_. In the hexapods, in the former Orders,
though there are usually three pedigerous segments, there is no
distinction of _dorsolum_, _scutellum_, &c. In the _Scolopendridæ_