head and prothorax of beetles, ought not to be overlooked. In many
Capricorns, as _Lamia Tribulus_, _speculifera_, &c., the disk and
sides are armed with short sharp spines; in others (_Stenocorus_,
&c.) the sutural and anal angles or one of them terminate in a spine
or tooth; sometimes the whole surface, as in _Hispa atra_, &c., is
covered, like a porcupine, with a host of slender spines, or its
sides defended by spinose lobes, as in _H. erinacea_: the humeral
prominence is armed with a spine pointing to the head in _Macropus
longimanus_, and forming a right angle with the elytrum in some
_Curculionidæ_, as _Rhynchites spinifex_; but the most remarkable
appendage of this kind is exhibited by _Cassida bidens_ and its
affinities,--from the centre of the sutures of the elytrum rise
perpendicularly a pair of long, slender, sharp processes internally
concave, which both apply exactly to each other, so as together to
form a single horn which rises, like a mast from a ship, from the
body of the animal[1806]. Besides the appendages here mentioned, the
elytra exhibit a variety of tubercles and other elevations of various
form and size, which it would be endless to particularize.
7. _Sculpture._ The _sculpture_ of the organs in question is very
various and often very ornamental: but as almost every kind of
it will be noticed in the _orismological_ tables, it will not
be necessary to enlarge upon it here, especially since I have
endeavoured upon a former occasion to explain how it may be useful
and important as well as ornamental to the animal[1807]. I shall
therefore only notice a few instances, amongst many, in which a
particular kind of sculpture distinguishes particular tribes. Amongst
those that are Predaceous the _Cicindelidæ_ have elytra without
striæ or furrows, while the majority of the subsequent terrestrial
tribes of this section are distinguished by them: the _Dynastidæ_ in
the Lamellicorn section are remarkable for a single crenated furrow
next the suture; in the weevil tribes the numerous species of the
genus _Apion_ are ornamented by furrowed elytra with pores in the
furrows, which give them the appearance of neat stitching; in many of
those beetles that have soft elytra, as the glow-worms (_Lampyris_),
the blister-beetles (_Cantharis_, _Mylabris_), and still more in
_Œdemera_, two or three slight ridges generally run longitudinally
from the base to the apex, and are visible also on the under-side;
as the _furrows_ probably lighten a _hard_ elytrum, these ridges
may serve to strengthen a _soft_ one, and it is by these that the
first approach is made to the reticular structure of _tegmina_ or the
wing-covers of _Orthoptera_: _Lycus palliatus_, &c., in its elytra
exhibits a direct resemblance of the reticulations of nervures.
8. _Clothing._ To what I have before said on this subject in
general[1808] I shall here add a few remarks, which, though they
more properly belong to _elytra_, may in many cases be extended to
the whole body of a beetle. In various instances it happens that the
beautiful markings of these organs, as in _Macropus longimanus_,
whose elytra when denuded are black, are produced by short decumbent
hairs; in some these variegations are the effect of scales resembling
those of _Lepidoptera_, often of a metallic lustre; from these
scales is derived all the brilliancy of the diamond-beetle (_Entimus
imperialis_, Germ.); in some the scales are so minute as to resemble
the pollen of flowers, as the white marks observable on the green
elytra of the rose-chafer (_Cetonia aurata_).
9. _Colour._ The organs of flight in the majority of the Orders
with respect to _colour_ are usually the most gaily decorated part
of insects; I therefore deferred the notice of that subject till I
came to treat of them. In general the colour of insects is either
inherent in the substance of their crust, or produced by the hairs
or scales that either partially or totally cover it. To confine
myself to the _Coleoptera_, of whose elytra we are treating, it may
be observed, I think, in general, that the majority of those that
feed upon _putrescent_ substances, the _saprophagous_ tribes of Mr.
W. S. MacLeay, are commonly of a more dark and dismal aspect and
colour than those which feed upon such as are living and fresh,
denominated _thalerophagous_ by the same learned author; this you may
see exemplified in his _Scarabæidæ_ and _Cetoniadæ_. Again, in the
Predaceous beetles a similar contrast of colours is often observable.
How brilliant and gay are the fierce _Cicindelæ_! those tigers of
insects, as Linné calls them; how black as to colour, how horrible
in aspect is their near relation the _Manticora_: what difference
exists in the economy of these animals is not known, except, as I
learn from Mr. Burchell, that the latter is subterraneous, whereas
the former seek the sunbeam and fly rapidly. I shall now point out
a few instances in which the colours of their _elytra_ distinguish
tribes or families. Amongst the Predaceous beetles a large family of
the _Cicindelidæ_ are distinguished by a middle angular white band,
and several white dots on their green or brown elytra, as in _C.
sylvatica_; a family of _Brachinus_, and the majority of _Mylabris_,
_Lamia capensis_ and _fasciatus_, &c., by black elytra, with yellow
or red bands; _Carabus violacea_ and affinities by the violet margin
of these organs; _Calliochroma_ Latreille by their _sericeous_, and
_Eumolpus_ by their _metallic_, lustre. These instances will be
sufficient to turn your attention to this subject, which though not
of _primary_ importance in discriminating genera &c., is not without
its use in a _secondary_ view.
10. _Uses._ I must not quit this subject without saying something
upon the ends which elytra seem designed to serve. Their first and
most obvious use is the protection of the wings when unemployed, that
they may not be lacerated or soiled, and rendered unfit for flight in
the various retreats to which these animals betake themselves either
for food, repose, or to lay their eggs; to promote this purpose more
effectually, the wings are usually curiously folded and laid up under
them; and where the elytra are very short, as in the _Staphylinidæ_,
these folds are very numerous and complex. In some instances,
however, as in _Molorchus_ F., _Atractocerus_, &c., the wings are
only partially protected by the elytra and not folded under them;
probably they are less in danger of laceration from their peculiar
habits than the generality. Another use is to protect the upper-side
of the alitrunk, which for reasons before assigned is usually softer
than the under-side, and also of the abdomen, often above nearly
membranous, from the injury to which they would otherwise be exposed;
in the latter part also the spiracles in _Coleoptera_ are not covered
by the inosculations of the segments, as is the case in most other
Orders, and therefore probably require some covering when the insect
is not flying. In the Apterous beetles this appears to be their
principal use; where these organs are connate, or as it were soldered
together, the back of the abdomen is a thin membrane; the appearance
of _two_ elytra in these cases is given, doubtless, for the sake of
symmetry and beauty, a subordinate attention to which may be traced
in all the works of creation. If we consider the bulk and weight of
many flying beetles, we may imagine that they want some assistance,
more than the extent and dimension of their wings seem to promise,
to support them in the air, and to enable them to move more readily
in it; and although it seems clear from the state of their muscular
apparatus that elytra do not move much in flight, yet by giving a
broad and concave surface to the air, for then they are usually
nearly vertical, they may assist in some measure as sails, and help
them in flying traversely and before the wind[1809].
ii. _Tegmina_[1810]. By this name the learned Illiger has
distinguished the upper organs of flight of the _Orthoptera_ and
Homopterous _Hemiptera_[1811]. They may be considered under the same
heads nearly as elytra.
1. _Substance._ _Tegmina_ differ very materially from _elytra_
in their _substance_, being generally more or less diaphanous,
though in _Blatta Petiveriana_ the dark parts are as opaque as
elytra, and those of the _Mantes_ that resemble dry leaves are only
semidiaphanous. These organs are also of a less dense substance
than elytra, something between coriaceous and membranous, which I
shall express by the term _pergameneous_, as somewhat resembling
parchment or vellum. Another circumstance relative to this head
also distinguishes them,--they are not lined with membrane. In some
instances, as in _B. Petiveriana_ just named, they approach nearly
to the substance of elytra, and in _B. viridis_, some _Mantes_, and
_Tettigonia_, &c., they are little different from wings in their
substance; but this does not diminish their right to be considered as
_tegmina_, since their structure is altogether the same.
2. _Articulation with the trunk._ I observed above that the axis of
elytra may be regarded as formed of _three_ parts, one appertaining
to each of the areas or their representatives[1812]; in _tegmina_,
and indeed in wings in general, these parts are separate and may
be more distinctly traced, the _axis_ of the _Costal_ Area being
generally the longest, and that of the _Intermediate_ often the
shortest; these _axes_ are suspended in the wing-socket by elastic
ligaments, intermixed with hard bony plates, the principal one of
which, called by M. Chabrier the _humerus_[1813], is connected both
with the _tegmen_ and the trunk, and in some a little resembles the
head and neck of a swan. This structure permits the animal to move
the lateral areas in some degree separately, so that each, especially
the _anal_, shall form an angle with the intermediate; as the motion
of the latter is not wanted, its _axis_ often falls short of the
base, or is obsolete, as in _Blatta_.
3. _Composition._ The three areas, traces of which we had discovered
in _elytra_, are particularly visible in _tegmina_. If you take any
cockroach (_Blatta_), you will at first sight see that in it they are
divided into three larger portions by stronger nervures or folds;
and if you also take a _Mantis_, or _Locusta_ Leach, a _Fulgora_ or
_Tettigonia_, the same circumstance will strike you, only you will
see that in these the intermediate portion terminates also in an
axis; these are what I call the three _areas_. The external one or
Costal is usually the longest and narrowest[1814]; the Intermediate
one is commonly triangular, with its inner side curvilinear[1815];
and the interior one, or _Anal_ area, in the _Orthoptera_ is rather
oblong; in _Fulgora_ angular, and in _Tettigonia_ it presents an
isosceles triangle; with its vertex to the apex of the wing[1816].
The first of these may be defined as that portion of the wing that
lies between the _costal_ and _postcostal_ nervures; and perhaps, in
some cases, as in _Mantis_, for there is the fold of the _tegmen_,
the _mediastinal_ may be regarded as its limit; the Intermediate
Area is that which lies between the _postcostal_ or _mediastinal_
nervure and the _anal_ fold of the wing; and the Anal Area is the
remainder. These areas may perhaps best be made out by tracing each
to its axis. To study them carefully in _tegmina_ and _hemelytra_ is
of considerable importance; for in them we find the first outline of
the general plan upon which the wings of insects are constructed,
and which, as we shall see hereafter, more or less enters into the
composition of them all.
4. _Position, and folding in repose._ With regard to their position
when not expanded, _tegmina_ vary somewhat in the different tribes.
In the _Coleoptera_ we have seen that, except in a few instances,
the elytra unite at their suture. Something like this takes place in
_Fulgora_, _Cercopis_ and affinities, in the Homopterous _Hemiptera_;
in these, though the union is not near so exact, yet the _tegmina_ do
not lap over each other; they are usually more or less deflexed, with
scarcely any portion in a horizontal position: in _Tettigonia_ F.,
_Chermes_, _Aphis_, &c., the middle part only of these organs meets,
from which point they diverge both towards their base and apex[1817].
In the _Orthoptera_ the position is quite different, for one tegmen
more or less lies over the other. In _Blatta_, in which the _tegmina_
are nearly horizontal, the left hand one covers almost half the
other[1818]: in the other tribes of the Order, with little variation,
the Anal Area of the _tegmen_ is horizontal, and covers the back of
the animal, and the Intermediate and Costal are vertical and cover
its sides; the former, however, in some cases, only forms the angle
between them. Sometimes in these the right-hand one is laid upon the
left, as in _Acheta_; and sometimes the reverse of this takes place,
as in _Acrida_ K. With regard to the folding of the _tegmina_, the
most remarkable instance that occurs is that of _Acheta monstrosa_,
in which the ends of both these organs and the wings, in repose, are
folded like a fan, and then rolled up like a serpent[1819].
5. _Shape._ The shape of _tegmina_ is various. In the _Blattæ_
and some _Mantes_ they are more or less _oblong_; in _Mantis
precaria_, _strumaria_[1820], and others, they incline to
_elliptical_; in _Phasma grandis_ and _Acheta monstrosa_ they
are rather _panduriform_[1821]; in _M. gongyloides_ they are
_semi-cordate_[1822]; in _Pterophylla trapeziformis_ they are
_rhomboidal_[1823]; in _Conocephalus erosus_ they are _sinuated_; in
_Locusta_ Leach they are usually _linear_ or linear-oblong[1824]; in
_Pterophylla_ K. they generally terminate in a short mucro[1825]; and
in some of those _Mantidæ_ whose _tegmina_ simulate arid leaves, in a
recurved one[1826]. In the Homopterous _Hemiptera_ the shape of these
organs is less various. In the _Fulgorellæ_ Latr. they incline to a
trapezium, sometimes to a pentagon[1827]; in the _Tettigoniæ_ F. they
approach to an obtuse-angled triangle; and in others of the tribe
they are nearly wedge-shaped[1828].
6. _Neuration._ The circumstance that most strikingly distinguishes
_tegmina_ from _elytra_ is their _neuration_ or veining; which adds
much to their strength, without increasing their weight so much as
to render them unapt for flight. To look at these organs in _Blatta
Petiveriana_, you would imagine them at first to be deprived of
this distinction; but if you observe them attentively, particularly
their white spots, you will soon detect their nervures; and if
you further examine their lower surface, you will find them very
visible. The gibbous _Blattæ_ also, _Blatta picta_ and affinities,
the analogues of _Erotylus_ amongst the _Coleoptera_, have _tegmina_
which, except at their apex, exhibit but faint traces of the nervures
of their tribe, and approach to elytra besides by the innumerable
minute impressed points that cover them. In the _Orthoptera_ and
some Homopterous _Hemiptera_ the nervures may be divided into
_longitudinal_ ones more or less ramified, and _traversing_ ones.
In the _Blattæ_ the traversing nervures cut the longitudinal ones
nearly at right angles, but not at regular intervals, so as to cover
the tegmen with quadrangular areolets; in _Mantis precaria_ and
affinities the longitudinal nervures of the Anal Area diverge from
the base, and are traversed nearly as in _Blatta_, while those of
the Costal diverge from the mediastinal nervure, but the traversing
ones form innumerable irregular reticulations; in _Mantis sinuata_
K.[1829] the whole tegmen has such reticulations but less numerous;
in _Locusta_ Leach it is regularly reticulated at the base, but the
areolets of the apex are quadrangular; in the _Mantes_, with oblong
wings, all are quadrangular; in _Pterophylla_ K. the longitudinal
diverging nervures are not numerous, and the traversing ones cut
them into quadrangular and triangular areolets, besides which they
are covered by innumerable impressed points, so as altogether to
exhibit a most exact resemblance of the leaf of some evergreen: in
_Gryllotalpa_ the longitudinal nervures of the Anal Area rather
converge towards the apex, are traversed by few transverse nervures,
and those of the Costal Area which diverge from the mediastinal
nervure by still fewer; the neuration of _Acheta_ F. has been before
described[1830]; I shall only observe here, that the constructors of
_stringed_ instruments of music might, perhaps, from the _tegmina_
of the male, the nervures of which probably modulate the sounds
which it produces, take a hint for giving the strings in them a
serpentine or convolute direction, and so might produce something new
in that department, corresponding with the serpents and French-horns
in _wind_ instruments. Of the Homopterous _Hemiptera_ in the
_Fulgorellæ_ Latr., which are most analogous to the _Orthoptera_
of all that tribe, the longitudinal nervures are more numerous and
branching, more especially toward the apex of the _tegmen_, and are
traversed as much by transverse ones, sometimes reticulating the wing
with roundish areolets, as in _F. laternaria_, and at others with
quadrangular ones, as in _F. candelaria_; in some of these however,
as _Otiocerus_ K., _Flata_ F., &c.[1831], there are no traversing
nervures; and these lead to the _Cercopidæ_ and others in which the
longitudinal nervures become few, and some are without any[1832],
and these terminate those of this section of the Order in which the
nervures in question are continued to the margin of the wing. We next
come to those, _Darnis_, _Centrotus_, _Membracis_, &c., in which they
are circumscribed a little within the apex by a traversing nervure,
so that the tegmen ends in a margin of pure membrane, and thus some
approach seems to be made to the _Hemelytra_, from _Tettigonia_, the
most conspicuous genus of this tribe, in which the _areolets_, few
in number, like those of _Lepidoptera_, are not formed, except the
terminal ones, by traversing nervures, but by the ramifications of
the longitudinal ones; in _Chermes_ the Intermediate Area, which is
connected with the base of the wing by a single nervure, is the only
part that has any areolets[1833].
7. _Colour._ Orthopterous insects are seldom remarkable for _tegmina_
of brilliant _colours_; there is in them none of that gilding or
metallic lustre which so often distinguishes elytra: they are also
frequently less ornamented in this respect than the wings, with which
they usually form an agreeable contrast. Their reticulations and
nervures, which are sometimes of a different colour from the rest of
the tegmen, decorate them considerably: a remarkable circumstance
belonging to this head attends the black tegmina of _Blatta
Petiveriana_; one has _four_ white spots, and the other only _three_;
but as one laps over the other, the symmetry of the arrangement is
preserved: the Homopterous _Hemiptera_ are more distinguished in
this respect, and some of the _Fulgoridæ_ imitate the _Lepidoptera_
both by their ocelli and spots: _Fulgora laternaria_, _Candelaria_,
_serrata_, and _Diadema_, sufficiently exemplify this remark, as do
several _Flatæ_ likewise[1834].
We may observe here--that _tegmina_ are more calculated for flight
than _elytra_, both from their thinner substance, and from the angle
that their Anal Area, and often the Costal, forms with the rest of
the _tegmen_; a circumstance which, in wings, M. Chabrier thinks
presents some facilities in that kind of motion.
iii. _Hemelytra_[1835]. The next species of wing-covers, which
though varying in the substance of their base, terminate in a part
distinct from the three areas, consisting in almost every case of
mere membrane, peculiar to the Heteropterous _Hemiptera_, are called
_hemelytra_, or half-elytra:--this term was also formerly employed,
but certainly incorrectly, to denote _tegmina_. I shall consider them
with respect to such of the particulars noticed under the former
heads as apply to them, but without repeating them formally.
1. As to their _substance_, they must be separately considered with
regard to their base and apex. In various instances the _base_,
or part consisting of the three areas, is almost corneous, as
in _Cydnus Morio_ and _bicolor_, bugs not uncommon with us, and
many others[1836]; in these cases it is lined with a _hypoderma_
like elytra; and in many the points, which are impressed upon it,
also perforate the _hemelytrum_, and seem to act as pores: but in
_Lygæus_, _Reduvius_, _Capsus_, _Miris_, and the majority of the
Heteropterous _Hemiptera_, the organs in question being soft and
flexible, may be stated as rather resembling leather than horn;--on
this account this part of a _hemelytrum_ is denominated the _corium_.
In _Scutellera_ the portion covered by the scutellum is membranous;
and in _Acanthia paradoxa_, and the cucullated species of _Tingis_,
the wing-covers are entirely so. The apex of these organs is almost
universally either membranous or coriaceo-membranous, on which
account it is called the _membrana_. I say _almost_, because in
_Aradus_ and the _Hydrocorisæ_ Latr., this part, though rather
thinner than the rest of the _Hemelytrum_, is also coriaceous; in
the latter tribe usually with a very narrow membranous edge; and in
many _Reduvii_ and _Zeli_ there is scarcely any difference in the
substance of the base and apex.
2. As to the _articulation_ of _Hemelytra_ with the trunk, it seems
not strikingly different from that of _tegmina_: the point or base
of the Intermediate Area, which falls short of that of the lateral
areas, seems connected by a slender ligamentous piece, with its axis,
which is thick; and I do not discern Chabrier's _humerus_ shaped like
a swan's head and neck[1837].
3. The _composition_ of these organs differs from that of _tegmina_
in more respects than one: in the first place, they consist, as
was lately observed, of _four_ instead of _three_ areas; in the
next, they appear to have, at least several of them, a part, which
I suspect to be analogous to that above described in _Coleoptera_,
supposed to represent the _phialum_ of wings[1838]. I shall first
speak of the _areas_. In some apterous species related to the
bed-bug, _Lygæus brevicollis_ Latr.[1839], &c., there is no trace
of the usual areas, and the _membrana_ is a very narrow strip; in
_L. apterus_ the former are very faintly traced out, but they are
present in all those that are furnished with wings; whence we may
conjecture that they are of the same importance in flight with the
folds observable in those organs[1840]. The three basal areas may be
said most commonly to present three isosceles triangles, the Costal
one being narrow and curvilinear[1841], the Intermediate the most
ample[1842], and the Anal one the narrowest and shortest[1843], with
its vertex towards the apex of the _Hemelytrum_, while in the two
former it is at its base. In _Lygæus compressipes_ (_Rhinuchus_ K.
MS.) the Anal Area is cultriform; and in most of the _Hydrocorisæ_ it
has an angle in the middle of its posterior margin. The proportion
that the _membrana_ or _apical area_ bears to the rest of the wing
varies in the different tribes. In some, as before stated, it is
obsolete, in others nearly so; in the majority, perhaps, it occupies
about a _third_ of the _hemelytrum_; in _Lygæus compressipes_,
_cruciatus_, &c., full _half_; in _Alydus calcaratus_, _two-thirds_;
in _Reduvius_, nearly _three-quarters_[1844]; and in _Aradus
depressus_ the corium,--divided, however, though indistinctly, into
the three areas,--is driven to the _base_ of the wing: two ends are
answered by this structure--as this insect lives under bark, its
thin _hemelytra_ take less room; and as it flies, though it has only
rudiments of wings, they are more fit to supply their place: the part
we are speaking of usually runs obliquely from the vertex of the
Anal Area to the base of the Costal.