_particularly_ the _neuration_ of the wings in the different Orders,
beginning with the _Coleoptera_. The first thing that strikes the
physiologist in surveying a wing belonging to an insect of this
Order, is the general arrangement of the nervures[1876]; which are
so placed that the required degree of tension may be given to every
part of this organ: thus some are nearly straight[1877]; others
run in a serpentine direction[1878]; others are forked with one
branch recurrent and another proceeding onwards[1879]; others again
are insulated, or do not originate from the base of the wing, or
from other nervures, but are merely placed to strengthen an open
space of it[1880]: these nervures are also usually broader and more
substantial than those of the wings of the subsequent Orders. Another
striking circumstance with regard to them is that the nervures form
few or no closed areolets, except in the Costal Area, where they
are inconspicuous; in _Dytiscus marginalis_, indeed, and _Tenebrio
Molitor_ one or two may be found, but in general there are none. In
many of this tribe the _postcosta_, which terminates at the joint
of the wing, becomes recurrent, so as to form a hook, which perhaps
represents the _stigma_, as in _Dynastes_[1881]; in _Creophilus_
K., a rove-beetle, there is no hook but a broad plate adjacent to
the _costa_. In the _Strepsiptera_ Order the neuration is extremely
simple, the nervures, except one insulated one, diverging from the
base of the wing[1882]: in this respect, as well as in the form
of that organ, an approach is made to the _Orthoptera_. In the
_Dermaptera_ this approach is still more evident; in the common
earwig[1883], the diverging nervures become numerous; between each is
an insulated one, taking its origin in the middle of the wing, and
running to the margin; a little nearer to the latter all the nervures
are dilated into a plate; those of the anal area are angular[1884],
and the exposed part of the costal is as hard as the elytra. The
neuration in the _Orthoptera_ Order may be called _radiate_, the
longitudinal nervures for the most part diverging from the base of
the wing like _rays_: in some few instances[1885], but not often, I
believe, an insulated nervure intervenes between each; traversing
or connecting nervures, cutting the longitudinal ones in various
directions, ornament these wings with an infinity of areolets,
causing them to resemble fine gauze or beautiful lace or net-work;
very often these areolets are quadrangular, sometimes rhomboidal,
frequently nearly circular, and differing occasionally, as has been
before observed[1886], in the different areas: it sometimes occurs
that there are no traversing nervures[1887], when the wing of course
is without areolets. In the Heteropterous _Hemiptera_ the type of
neuration, as to the wing, seems borrowed from the _Coleoptera_, a
further proof that these are the analogues of that Order amongst
the _Haustellata_ Clairv. In these the nervures usually are few and
dispersed, and seldom form any closed areolets. If you examine any
_Scutellera_, _Pentatoma_, or _Lygæus_, you may trace the uncinated,
forked, serpentine, and insulated nervures of Coleopterous insects;
in _Gerris_ and _Velia_ there is an approach to the neuration of
some _Homopterous_ species, and in _Belostoma_ &c. the wing is
reticulated by _spurious_ nervures. In the Homopterous section
there are several types of neuration; thus the _Fulgoræ_ resemble
the _Orthoptera_ in this respect; while the _Tettigoniæ_ F., &c.,
approach nearer to the _Hymenoptera_ and _Diptera_, and have their
apical areolets circumscribed _within_ the margin by a traversing
nervure; in _Flata_, &c., the areolets are mostly formed, not by
traversing nervures, but by the branching of the longitudinal ones;
in this respect they are not unlike the _Lepidoptera_. In this
last-named Order there are some variations with regard to their
neuration--thus, amongst the _butterflies_ in _Urania_, &c., there is
no closed areolet in any of the wings, and almost all the nervures
diverge from the base[1888]; in _Morpho_, &c., there is only one in
the primary wing[1889]; in _Heliconia_, &c., there is one in both
wings; amongst the _moths_, in the _Bombyces_ L., this is divided
into _two_, and in _Cossus labyrinthicus_ Don. into _three_ areolets:
in some butterflies (_Lycæna_) there is one insulated nervure[1890],
and in others (_Hesperia_) there are two[1891]; in these two last,
and _Heliconia_, _Urania_, &c., the end of the Costal Area is
divided into several areolets by oblique nervures[1892], which
gives them some analogy to the wings of many _Neuroptera_; and at
the base of this Area, in _Morpho_, is a roundish areolet[1893]. In
this Order the externo-medial and interno-medial nervures coalesce
into one, and are only represented separately by their first and
third branches[1894]. In the _Neuroptera_ Order the general type
of neuration is borrowed from the _Orthoptera_; but in _Osmylus_,
_Termes_, &c., there is an approach to that of _Flata_ in the
Homopterous _Hemiptera_, and in _Psocus_ to others of that section;
in the second of these genera the nervures, except those of the
costal margin, are spurious.
I now come to the Order in which M. Jurine has laboured with so
much success, I mean the _Hymenoptera_; and I only regret that his
labours were directed to so small a portion of the Class _Insecta_,
and in that portion only to a part of the upper wing; I say only
a _part_, because all those areolets of the posterior part of the
wing, in some cases amounting to _five_[1895], that lie behind his
_cubital cellules_, are not employed by him as diagnostics, and are
left without a name. By dividing the areolets of the Intermediate
Area of these wings into _three_ portions, the _basal_, _medial_,
and _apical_[1896], I have endeavoured to remedy this defect, and by
naming each set of areolets in the middle portion, as you will see in
the Orismological Definitions, under the term _Areolets_, you will
find it easy to describe any given areolet and its place in the wing;
those of the base may be called the _anterior_, _intermediate_, and
_posterior_, where _three_ occur; and the first and last of these
terms will suffice where there are only _two_; the apical areolets,
or those that are open to the margin, may be called, _first_,
_second_, and _third_ in the order of their occurrence, reckoning
from the anterior or costal margin.
In this Order it is curious to trace the progress of neuration in
the wings of different genera. Thus in _Psilus_ only the _costal_
nervure and the _stigma_ are to be traced[1897]; in _Chalcis_ the
_postcostal_ and _stigma_[1898]; in _Codrus_ and _Leucospis_ the
_costal_, _postcostal_, _stigma_, and a nervure representing the
_externo-medial_ and _interno-medial_ coalescing into one[1899];
in _Omalus_ the _basilar_ areolets appear[1900]; in _Crabro_ both
_basilar_ and _medial_[1901]; in _Cynips basilar_, _medial_, and
_apical_[1902]; and in _Hylotoma_ the wing is filled with its
greatest complement of areolets[1903]. The medial areolets of
the Intermediate Area, as you will see in the definitions, form
_three_ distinct series; these may be called the _protomesal_,
_deuteromesal_, and _tritomesal_, reckoning from the postcostal
areolets; the first of these corresponds with the cubital cellules of
Jurine. These series may be expressed, according to the number of
their areolets; by figures, the protomesal standing first. They vary
much in this respect in the different genera. Thus in _Cyclostoma_
K.[1904], reckoning the didymous areolet as two, the numbers
will stand 4:2:1; in _Hylotoma_, &c., 3:2:1[1905]; in _Aulacus_,
&c., 2:2:1[1906]; in _Bracon_, &c., 2:1:1[1907]; in _Chelonus_,
2:0:1[1908]; in _Cynips erythrocephalus_ Jur., 2:0:0[1909]; in
_Formica_, 1:1:1[1910]; in _Oxybelus_, 1:0:1[1911]; in _Chrysis_,
0:1:1[1912]; and in _Cynips Rubi_ K., 1:0:0[1913]. The most natural
number is 3:2:1. The next in importance to the medial areolets of the
Intermediate Area are the _apical_, or those open to the margin; the
most usual number of them, excluding the postcostal areolets which
belong to the Costal Area, is _three_; but in _Sirex_ there is an
approach to _four_[1914]; in _Evania_ there are only _two_[1915];
and in _Philanthus_ there are none[1916]; in many, as _Prosopis_,
_Nomada_, _Andrena_[1917], though there is the usual number, they
are incomplete and do not reach the margin. The _basal_ areas are
of little importance in assisting to determine genera; they are
most commonly _two_ in number, but in _Cynips_, &c., there is only
_one_[1918]. The shape and other circumstances of the areolets vary
considerably in different genera and species: upon these however
I shall not enlarge further, but proceed in the next place to
consider very briefly the wings of the _Diptera_ Order as to their
neuration. These are not so easily made subservient to a general
plan. The _basilar_ areolets are now reduced considerably in length,
occupying merely the base of the wing[1919]; the _medial_ are become
less numerous and important[1920]; and the _apical_, in a variety
of instances, are the most conspicuous[1921]; in some wings, as in
those of _Penthetria_, the Intermediate Area has no nervures or
areolets, or only spurious ones; in _Psychoda_ the nervures diverge
from the base almost without branching, so as to form no closed
areolets[1922]; in many, the lower medial areolets are very long,
resembling the basilar in _Hymenoptera_[1923]; these are often
crowned by a single small one, as in the _Stratyomidæ_, _Tipula_,
&c., from which numerous branches proceed to the margin[1924]; but in
_Musca_ two large ones approach the margin, the anterior one having
an angle open to it[1925]; in the _Hippoboscidæ_ almost the whole of
the wing is occupied by the apical areolets[1926]; though in some
cases they are incomplete[1927].
4. I am next to consider the _position_ of wings in _repose_ and
their _folding_. The most important object of this is that when
unemployed they may occupy less space, be less in the way of the
insect, and be most effectually protected from injury. Another end is
also served by this structure,--that wings can thus be very ample,
and present a large surface to the action of the atmosphere without
incommoding the insect when it has not occasion to use them.
With respect to this head, insects may be divided into _two_
classes--namely, those whose wings in repose are covered by
wing-cases harder than the wings themselves, and those that have
no such protection. In the former the wings, though the rule
admits several exceptions, have more folds than in the latter. As
the different mode of folding the wings has been assumed for a
characteristic of the earlier Orders, I shall explain to you with as
much brevity as possible how each is circumstanced in this respect,
beginning as usual with the _Coleoptera_.
There are _two_ principal folds of the wing in this Order, which
may be named the _anal_ and the _apical_: the _former_ is when
the Anal Area or part of it is folded on the under surface of the
base of the wing; this fold is always more or less _longitudinal_:
the _latter_, the apical fold, is by means of the _commissura_
or joint of the _postcosta_ lately mentioned: which in _Hister_,
_Staphylinus_, &c., for obvious reasons[1928] is nearer the base
of the wing; in _Necrophorus_ in the middle; in _Dynastes Aloeus_
beyond the middle[1929]; in _Tenebrio Molitor_ near the apex; and
in _Dytiscus marginalis_ there appears to be no joint at all; but
the fact is, that in this insect the _postcosta_,--the termination
of which really forms the joint, the _costa_ itself being only
flexible at that point,--stands at a greater distance from the latter
at its end. Well, at this joint the above fold is made, the apex
of the wing, being first folded longitudinally, turning under and
inwards, and forming an angle, more or less acute, with the joint or
costal margin, so that the fold is not quite but nearly transverse:
this at least is the case in _Geotrupes stercorarius_ and other
Lamellicorns: in _Staphylinus_, &c., there are several transverse and
longitudinal folds, and thus the wing is more easily packed under
the short elytra; in _Molorchus_, _Necydalis_, &c., in which it is
left uncovered, except at its base, the anal fold takes place, and
the apical in some degree; a short portion near the apex forming an
obtuse angle with the margin; in _Atractocerus_ the wing appears to
be only _longitudinally_ folded; and in _Buprestis vittata_ only
the _anal_ fold is to be detected. Besides these transverse and
longitudinal folds these organs, in many beetles, have an infinity of
fine corrugations, which ramify like the nervures of the _tegmina_
of _Flata_[1930], &c., proceeding from the Costal Area or the disk
of the wing to the posterior margin; the object of these plicatures
is doubtless to present a more ample surface to the action of the
atmosphere in flight[1931]. When all these folds have been made in
a Coleopterous wing, the apex of the one at its posterior margin
crosses or rests upon that of the other[1932].
In the _Dermaptera_[1933], at least the common earwig, there is a
triple transverse fold of the wing, and besides this it has numerous
longitudinal ones like those of a fan, each of the diverging nervures
representing one of the sticks. In the _Strepsiptera_ the folds
are only longitudinal; a circumstance which, besides the form and
neuration of the wing, sufficiently attests that its station is
more near the _Orthoptera_ and _Coleoptera_ than the _Diptera_. We
next come to the _Orthoptera_[1934]; in these the folds in general
are longitudinal; and those of the Anal Area in particular, either
in whole or in part, exact counterparts of a fan: wherever there
is a straight nervure, there is usually a fold or a tendency to
it; this is the case even with the short oblique ones observable
in the Intermediate Area of _Blatta_: in this tribe the Anal Area,
or a considerable portion of it, is folded under the rest of the
wing, and the whole lies on the back of the animal, so that in this
wing there are only two primary folds; but in those with a narrower
body, as _Phasma_, &c., there are more, and the Anal Area, folded
like a fan, lies horizontally on the back; the Costal is vertically
applied to the sides, and the Intermediate is between both, as in the
_tegmina_[1935]. In _Gryllus_ Latr., _Gryllotalpa_, &c., when the
wings are folded, the end of the Anal Area projects so as to present
the appearance of two tails[1936]; and in that remarkable Chinese
animal _Gryllus monstrosus_, in which these tails are very long,
they are convolute like those of some quadrupeds[1937]. It is to be
observed that in the secondary folds of these wings the angles of the
folds are surmounted by a nervure.
In both sections of the _Hemiptera_ Order, as in the _Coleoptera_,
the Anal Area is turned under the wing and lies over the back of
the insect; this is the only _primary_ fold, but besides there are
several longitudinal semifolds or _secondary_ ones, in which one
part of the surface forms an obtuse angle with another; and in
_Tettigonia_, &c., these folds ramify in the wings as well as in
the _tegmina_ at the margin: a number of semifolds also, sometimes
transverse and sometimes oblique, run in pairs from each side of
every nervure of the disk of both _tegmina_ and wings in the genus
last named, the use of which has been before mentioned[1938].
We now come to those Orders that have _four_ membranous wings: first,
I shall consider the _Lepidoptera_. With respect to the position of
their wings in repose some variations take place. In the majority
of the _day-fliers_ (_Papilio_ L.), when the animal reposes the
wings are applied to each other by their upper surface so as to be
_vertical_; but in the skippers (_Hesperia_), the secondary wings
assume a _horizontal_ position, while the primary are _vertical_ but
applied to each other. In the _Crepuscular_ tribes (_Sphinx_ L.)
the upper wings are incumbent on the lower, and deflexed. In the
_night-fliers_ (_Phalæna_ L.) the types of position are various.
In some _Attacus_, _Saturnia_, _Noctua_, &c., the wings cover each
other, and are a little inclined from a horizontal position; in
_Gastropacha_, _Odenesis_, and some other _Bombycidæ_, they are
deflexed, and the anterior margin of the under wing projects beyond
that of the upper: in some of the _Tineæ_ L., as _Crambus_, the wings
are convoluted, and in others, _Galleria_, they are applied close to
the sides of the body, and being elevated at the apex, terminate, to
use a French term--_en queue de coq_: in _Noctua_, _Geometra_, &c.,
the wings usually cover the abdomen, and are nearly horizontal. With
regard to the _folds_ of their wings, the Anal Area of the secondary
is the only part that has any striking one; in _Papilio Hector_
and affinities it turns up so as to defend the sides and part of
the back of the abdomen; in _Morpho Teucer_ it turns down, and
meeting that of the opposite wing, forms a semitube which receives
and shelters that part below. In the _Crepuscular_ and _Nocturnal_
Lepidoptera this fold, especially in the former, is very slight. With
respect to semifolds in the _Diurnal_, there is one originating in
the disk, between each of the nervures, that goes to the margin of
the wing; likewise the under wings, particularly of many _Noctuæ_,
_Arctiæ_, &c., have many longitudinal semifolds.
In the _Neuroptera_ Order several variations take place with regard
to the _position_ of these organs in repose: thus, in _Æshna_,
_Libellula_, &c., they continue expanded; in _Argion_ they are
applied to the body; in _Myrmeleon_ the upper are horizontally
incumbent on the lower; in _Hemerobius_ they incline to the horizon.
With regard to their _folds_ in _Æshna_, &c., the longitudinal
nervures alternately form the summit or the bottom of a semifold, as
do those branches that terminate in the posterior margin; this kind
of plicature may be observed, but in a less degree, in _Ascalaphus_,
_Myrmeleon_, &c.; in _Panorpa_ every nervure is the ridge of a
slight fold; in _Termes_, on the contrary, it forms its bottom. In
the _Trichoptera_, the under wing being much more ample than the
upper, the Anal Area forms a fold under the wing, and there seem
longitudinal secondary folds besides.
We now come to the _Hymenoptera_. In this Order the wings, as to
their position in repose, are usually incumbent upon each other,
and cover the abdomen; in the _Vespidæ_, however, they are placed
parallel to the body, but do not cover it. Before I notice the
plicature of these wings, I must recall your attention to what I
lately observed[1939] with regard to Jurine's _bullæ_ (bubbles),
but which are really the _joints_ of the nervures, as they are to
be found only where the folds pass; and where they exist they are
an index by which the folds, or rather semifolds, may be traced. I
counted eleven of these little joints in the upper wing of _Andrena
cineraria_; sometimes, however, instead of a _bulla_, a nervure
stops short to admit the fold. Wings in this Order have often three
longitudinal semifolds more or less conspicuous; these you may
trace in the saw-flies (_Tenthredo_ L.), whose wings Linné terms
_tumidæ_, by which term he would indicate the elevation of the
whole surface produced by this structure; in the under wings of
these, and _Scolia_, _Bembex_, &c., the Anal Area is turned under
the wing, as in many preceding tribes[1940]: in _Sirex_, &c., that
Area of the upper wing turns upwards, forming an acute angle with
the rest of the organ; the same circumstance distinguishes the under
wing in the _Ichneumonidæ_. Several apical semifolds, marked by a
pellucid streak, distinguish _Tiphia_ F., and in _Bombus_, _Bembex_,
&c., an infinity of branching ones, like those before described in
_Coleoptera_, corrugate the apical margin. In the _Vespidæ_ the
_upper_ wings are folded longitudinally into _three_ nearly equal
portions, but in the _under_ ones the Anal Area only forms the fold.
In the _Diptera_ Order, as to their _position_ when at rest, the
wings are mostly incumbent one on the other; but in _Psychoda_
they are deflexed, so as to form a kind of penthouse. With regard
to their _plication_, in some, _Tipula oleracea_, &c., a slight
oblique semifold runs from the _stigma_ to the apical margin, and
the Anal Area has two, as it has in many _Muscidæ_, itself forming
nearly a right angle with the rest of the wing; besides these it is
corrugated with minute transverse semifolds, which are observable
also in several other Dipterous insects; in many _Stratyomidæ_ they
are oblique, and run from the disk to the posterior margin; and in
_Asilus_, _Bombylius_, &c., they are wavy.
5. We are next to say something upon the _shape_ of wings: this,
though apparently extremely various in the different Orders and
tribes, may I think be traced in every wing to one original
prototype, a _triangle_ with the largest angle rounded and subtended
by the anterior or costal margin: in some, as the _Coleoptera_,
_Orthoptera_, &c., this type of formation is a _right-angled_
triangle[1941]; and in others, as in the _Hymenoptera_, _Diptera_,
&c., the majority of the _Neuroptera_, &c., it is an _obtusangled_
one[1942]; it may be further observed, that in receding from these
forms wings very often assume that of the half or quadrant of
some regular figure, as we shall see when we consider those of
the different Orders. Another general observation I shall first
mention,--that these organs are universally narrowest at their
base and widest at the apex, provided we consider as the apex the
termination outwards of the three Areas; otherwise we might say
that wings in the _Coleoptera_, _Orthoptera_, &c., were wider at
the base than at the apex[1943]. The wings in the former Order, and
in several of the Heteropterous _Hemiptera_, as _Gerris_, _Velia_,
&c., may in general, as to their _shape_, be termed semicordate
or semiovate[1944]; in the _Dermaptera_ they incline to an oval
figure[1945]: in the _Strepsiptera_, _Orthoptera_, most Homopterous
and many Heteropterous _Hemiptera_, they approach to the quadrant
of a circle; in a considerable portion of the _Lepidoptera_ the two
under wings, if united at their posterior margin, approach a circular
form; the upper ones vary a little from the prototype of the under
ones, forming an obtusangled triangle[1946]; in many _Neuroptera_
the _primary_ wings may be called oblong or linear-oblong, while the
_secondary_ betray more evidently the _right-angled_ or _obtusangled_
triangle; in the _Hymenoptera_ this latter form is every where
conspicuous, with little deviation, except in the rounding of the
angles[1947]; and, finally, in the _Diptera_ this form shades off
again into an oblong, ovate, or linear shape, the wing being most
commonly attenuated at the base into a kind of footstalk[1948]. Some
singular variations with respect to the termination or marginal
processes of the wings are exhibited by many _Lepidoptera_; thus in
_Attacus Atlas_, &c., the primary wings are falcated or hooked at
their apex[1949]; and in great numbers both wings are there scolloped
into alternate bays and capes, if I may so speak, varying in depth
and length[1950]. There is usually a sinus between every pair of
nervures, each of which terminates in the adjoining prominence, as
a fold does in the sinus[1951]. Where present, in the _primary_
wings there are _eight_ of these sinuses, and in the _secondary_,
where they are most usual, _seven_; some are remarkable for the long
_tails_ which distinguish their secondary wings; those in _Papilio_
are usually an elongation of the fifth, from the anterior margin, of
the prominences before mentioned, into a spathula-shaped diverging
process, varying in length and width[1952]: but in _P. Ulysses_ it
does not diverge; and in _P. Podalirius_ it is linear. They are
found also in other subgenera; thus in _Urania Patroclus_ there are
_two_; in _U. Riphæus_ _three_; in _Erycina Cupido_ _five_; and in
_E. Endymion_ _six_ of these tails; in some, as in _E. Dorylas_, the
whole wing seems to form the tail; in others again, as in _Hesperia
Proteus_ and _Bombyx Luna_, it is an elongation of the anal angle.
Other wings in this Order are divided into lobes resembling feathers,
as you may see in _Pterophorus hexadactylus_, &c.[1953]