_ramification_ of these organs, and their _plumage_. By attending
to this, you may often detect the sexes in an instant; since the
antennæ of the males in numerous instances are much more complex than
those of the females. For what end the Creator has so distinguished
them is not quite clear; but most probably this complex structure
is for the purpose of receiving from the atmosphere information of
the station of the female. A tendency to branching will be found in
the antennæ of some males, in tribes where these organs are usually
perfectly simple in both sexes. Thus, in the male of _Chelostoma
maxillosa_,--mistaken for another species by Linné, which he names
_Apis florisomnis_,--the intermediate joints on their inner side
project into an angle[782]; and those of the same sex of the common
hornet, by means of a central sinus, have two obtuse teeth on each.
With regard to more direct ramifications, some male antennæ terminate
in a fork, or two branches. This is the case with _Hylotoma furcata_
Latr., a saw-fly[783]; and the peacock-louse (_Nirmus Pavonis_
Herm.)[784]. Others, again, have three lateral branches, as in
_Eulophus_ Geoffr. a little parasite, the male antennæ of which send
forth a hairy external and rather long branch, from the base of the
fourth, fifth, and sixth joints[785]. In _Elater flabellicornis_
L., the eight last joints are flabellate, or elongated and flat,
resembling the sticks of a fan in the male[786]; in the female they
are shorter, and more properly may take their denomination from the
teeth of a comb. In _Lampyris Latreillii_ Kirby, the antennæ of the
former are flabellate on both sides, while those of the latter are
little more than serrate[787]. These organs are extremely beautiful
in the males of the _Rhipiceræ_ of Latreille. In _R. marginata_ K.
they consist of thirty-two joints, from thirty of which issues a
branch, the first very short, but the rest gradually increasing in
length as they approach the middle of the antenna; then gradually
decreasing to the end, so as to represent an expanded fan[788]. But
in none are they altogether so remarkable as in those moths that
Linné denominates _Bombyces Attaci_, and some others. In these, in
the males, these organs in their contour are lanceolate, and every
joint is furnished with a couple of parallel equal branches on each
side[789]. In the females these branches are shorter on the whole,
and alternately one long and one short; but in some, as _Saturnia
Pavonia_, there is only one short branch or tooth on each joint in
this sex[790]. In _Bombyx regalis_ &c. only the first part of the
antenna is so branched; and those of the female are setaceous and
without branches. In _B. versicolor_, &c. there is only one branch
from each side on every joint; those of the female being much shorter
than those of the male. The latter sex of _Pteronus Laricis_ Jur., a
saw-fly, afford an example of a different structure, the antennæ on
one side sending forth a branch from every joint but the two first;
but on the other side, the nine or ten last joints also are without
a branch. The female antenna is serrated[791]. In another of this
tribe, _Pterygopterus cinctus_ Klug, the male antenna resembles a
single-toothed comb, being branched only on one side: that of the
female, like the former instance, is serrated[792]. Whether the
remarkable antennæ that distinguish the known individuals of the
genus _Phengodes_ (_Lampyris plumosa_ F.) is a sexual character
has not been ascertained; but it is not improbable that it may be,
as in other _Lampyridæ_. A pair of delicate flexile and almost
convolute plumose branches proceeds from the apex of each joint
except the basal ones, which have something the air of cirri, and
give a more than usual degree of lightness and elegance to these
organs[793]. Other antennæ, especially in the _Diptera_ order,
assume an appearance of _plumes_--not from the branches that proceed
from them, but from the fine long hairs that beset and adorn them.
These are universally indications of the male sex, those of the
females being generally comparatively naked. If you take the common
gnat, you will find that the antennæ of one individual are thickly
fringed on each side, and tufted at the end with fine long hairs,
while in the other only four or five placed at intervals in a
whorl are to be perceived[794]. In _Chironomus_ Meig., a kind of
_Tipula_ L., resembling a gnat, the male antennæ are beset on all
sides with the finest hairs, and resemble a beautiful plume[795],
while the females to the unarmed eye appear naked. Even in some
_Hymenoptera_, the antennæ of the males are thus feathered, in a less
degree: for instance, in _Hylotoma_ Latr.[796] Whether the tufts and
fringes which ornament, in a remarkable manner, the antennæ of many
_Cerambycidæ_[797], are sexual characters, is not certainly known.
We are now to consider other sexual differences in these organs,
resulting from the size or configuration of one or more _individual
joints_. To begin with the first joint, or scapus. In many of
the _Hymenoptera_, particularly the _Anthophila_ Latr., this is
elongated, and the remaining joints form an angle with it in the
females: while in the other sex it is much shorter, and in the
same line with the rest of the antennæ; and in _Hylæus dilatatus_
(_Melitta dilatata_ Kirby) the first joint in the male is dilated and
shaped something like a patella[798]. In _Malachius bipustulatus_,
&c. the sex just mentioned is peculiarly distinguished by a white
excrescence on the first four joints of the organs in question,
most conspicuous in the second and fourth. The antennæ of male
_Cerocomæ_ are not very different[799]. Mr. Marsham has described
a little _Haltica_ under the name of _Chrysomela nodicornis_, from
a peculiarity of the same sex not to be found in the other. The
fourth joint is very large and obtriangular; in the female it is
merely longer than the rest. In _H. Brassicæ_ and _quadripustulata_
the fifth joint is larger and longer than all but the first in the
male, in their females it is only longer. In some moths (_Herminia_
Latr., _Crambus_ F.) there is also a knot in the middle of the male
antennæ[800]. In _Noterus_, a water-beetle, the six intermediate
joints are thicker than the rest, beginning from the fourth, and the
last but one ends internally in a truncated tooth. The fifth and
two following joints in the male antennæ of _Meloe_ are larger than
the rest, which distinguishes them, as well as a remarkable bend
observable at that part[801].
Variations of the kind we are considering are also observable in
the _clava_, or knob, in which antennæ often terminate. You have
doubtless observed that the lamellated clava of the antennæ of
the common cockchafer is much longer and more conspicuous in some
individuals than in others--the long clava belongs to the male[802].
In another species, _M. Fullo_, that of this sex is nine or ten
times the length of that of the other. In _Colymbetes serricornis_,
a water-beetle, the male has a serrated clava of four joints. In
_Dorcatoma dresdensis_[803], and also _Enoplium damicorne_, two
beetles, it is nearly branched in the male, but much less so in
the female. In a little destructive beetle, common in our houses
(_Attagenus Pellio_), in the latter it is very short, but in the
former it is very long, and nearly formed by a single joint. In
_Eurhinus_ Kirby, a New Holland genus of the weevil-tribe, in
the male the last joint, also, is much longer than it is in the
female[804]. These examples will give you some idea of the principal
variations that take place in the antennæ of the sexes, and of the
wonderful diversity of forms in this respect to which mere sexuality
gives rise amongst insects.
In the _eyes_, or _stemmata_, this diversity is less remarkable.
Latreille has described two ants, _Formica contracta_ and _coeca_, in
the neuter of which he could discover no eyes[805]: in the former,
the female, however, had large ones. The male he appears not to
have known, but it probably was not destitute of these organs; of
the latter he was acquainted only with the workers. The neuter of
_Myrmica rubra_, another ant, has no ocelli or stemmata, although the
male and female are provided with them[806]. They are discoverable
only in the former sex of that singular insect related to the ants,
_Mutilla europæa_. Other insects differ in the _size_ of the eyes
of their sexes. In the hive-bee, and some _Ephemeræ_, the eyes of
the drone or male are much larger than those of the worker and
female, and also meet at the vertex, having their stemmata below the
conflux; whereas in these latter they are widely distant[807]. In
_Stratyomis_, _Tabanus_, and many other two-winged flies, the _male_
eyes meet at some point below the stemmata, and above the antennæ.
In the former they touch more at an angle; for the vertex forming
a narrow isosceles triangle, and for the anterior part of the face
one nearly equilateral: while those of the _female_ are separated
by a considerable interval. In _Heptatoma_ and _Hæmatopota_ in that
sex, a similar interval obtains; while in the other, after forming a
minute short triangle, they unite for a considerable space, and then
diverging, form the face. This is also the case in _Tabanus_; but in
the female, the space that intervenes between the posterior part of
the eyes is much narrower than in these two cognate genera of the
horse-flies. In some others of this order, as _Musca_ Latr., the eyes
of the male do not touch, but approach posteriorly much nearer to
each other than those of the other sex. In a few instances the sexes
vary even in the number of their eyes, as well as the size. This
occurs in some species of _Ephemera_ L. (_E. diptera_, &c.), in which
the male, besides the common lateral ones, has two large and striking
intermediate eyes, that sit upon vertical pillars or footstalks[808].
2. The _Trunk_. The thorax of many coleopterous males, especially
of the _Dynastidæ_ and _Copridæ_ amongst the petalocerous tribes,
exhibits very striking differences from that of the female. In
many _Lucani_ the lateral angle is more prominent. In _Anthia_
it is bilobed posteriorly, while in the last-mentioned sex it is
entire[809]. In _Phanæus carnifex_ MacLeay (_Copris_ F.) it is
elevated into a plane triangular space, with the vertex of the
triangle pointing to the head; but in the female it is convex, with
an anterior abbreviated transverse ridge[810].
In a large proportion terrific _horns_, often hollow, like those
of the head lately noticed, arm the thorax of the male, of which
you will usually only discover the rudiments in the other sex. In
the first place, some are _unicorns_, or armed only with a _single_
thoracic horn, which frequently, in conjunction with the thorax
itself, not a little resembles a tunnel reversed: of this description
are _Dynastes Hercules_, _Tityus_, _Gedeon_, _Enema_, &c.[811] In
the three first this horn is porrected, or nearly in the same line
with the body; but in the last, and _D. Pan_, it forms an angle with
it; and in _D. Ægeon_ it is nearly vertical[812]. In _D. Hercules_
it is very long; in _D. Alcides_[813] and _Tityus_ very short; in
the two last, and in _Oxytelus tricornis_ which is similarly armed,
it is undivided at the apex; but in _D. Gedeon_, _Pan_, _bilobus_,
&c.[814] it is bifid or bilobed. It is usually rather slender, but
in _D. Chorinæus_[815] and _bilobus_, it is very stout and wide.
In _D. claviger_ it is hastate at the apex[816]. In _D. hastatus_
it is short and truncated[817]. Others, again, have _two_ thoracic
horns. In _Copris nemestrinus_ these are discoidal, diverging, and
inclining forwards[818]. In _Phanæus floriger_[819] they are lateral,
triangular, and incline towards each other, with, as it were, a
deep basin between them. In _P. splendidulus_ they sink into two
longitudinal ridges, most elevated posteriorly, with an intervening
valley[820]. In _P. bellicosus_ they are posterior, compressed,
truncated, and emarginate at the apex, and include a basin[821]. In
_Copris Sabæus_ they are merely two acute prominences[822].--_Three_
horns distinguish the thorax of many. In _D. Aloeus_[823] and its
affinities, they are arranged in a triangle, whose vertex is towards
the head. In _D. Antæus_[824] these horns are nearly equal in
length, and undivided at the apex. In _D. Titanus_[825] the anterior
horn is longer than the rest, and bifid at the apex; in _D. Atlas_
and _Endymion_[826], both of which have a horn on the head, it is
much shorter. In others, as in _Megasoma_ Kirby, the vertex of the
triangle is towards the anus. In _M. Typhon_[827] it is longer than
the anterior ones, and bifid at the apex; in _M. lanigerum_ they
are equal in length[828]. In _M. Elephas_ and _Actæon_[829] it is
merely an elevation of the thorax; in the last almost obsolete. In
_Geotrupes Typhæus_, common on our heaths, the anterior of this part
is armed by three horizontal horns, the intermediate one being the
shortest[830]. _Copris lunaris_ also, another of our own beetles,
has three short posterior thoracic horns, two lateral and triangular
ones, and a transverse intermediate elevation, with a notch in the
middle[831]. In _Dynastes Neptunus_ the horns are porrected, the
middle one being very long, and the lateral ones short[832]. In _D.
Geryon_ the point of the lateral horns is towards the anus, and
the base of the intermediate one covers the scutellum[833]. Others
have _four_ of these singular arms: this is the case with one of
our rarest beetles, _Bolbocerus mobilicornis_ K., which has four
dentiform horns, the intermediate pair being the shortest, arranged
in a transverse line on the anterior part of the thorax[834]. In
_B. quadridens_ these are merely teeth. In _Phanæus Faunus_[835] it
has two lateral, elongated, compressed, truncate, horizontal horns,
and two intermediate teeth. _Dynastes Milon_ has a still greater
number of horns on the thorax of the male, there being two lateral
anterior ones and three posterior ones--the intermediate being the
longest[836]; and _Copris Antenor_ Fabricius and Olivier describe as
having a many-toothed thorax; and from the figure of the latter[837],
the male appears to have seven prominences.
But the males of insects are not only occasionally distinguished by
these dorsal arms--in a few instances they are also furnished with
_pectoral_ ones. The illustrious traveller Humboldt found in South
America a species of weevil (_Cryptorhynchus Spiculator_ Humb.), the
breast of which was armed with a pair of long projecting horns; and
I possess both sexes of four species, three at least from Brazil,
that exhibit in one individual the same character. One, concerning
the country of which I am uncertain, recedes somewhat from the type
of form of the rest, and comes very near that of _Rynchænus Strix_
F.[838] In the individual which I take to be _C. Spiculator_, the
pectoral horns are very long, curving upwards at the apex, and
nearly in a horizontal position; while in the three others they are
much shorter, and inclined towards the horizon. The males of some
species of _Rynchites_, as _R. Bacchus_ and _Populi_[839], are also
armed with a pair of lateral horns or spines, which may be termed
pectoral rather than dorsal.
I shall now advert to the sexual characters that are to be found in
the _instruments of motion_ attached to the trunk--beginning with
those for _flight_. In the female of the common glow-worm (_Lampyris
noctiluca_) not the slightest vestige of elytra or wings is visible,
and it resembles a larva rather than a perfect insect; yet its
mate is a true beetle furnished with both. The same circumstance
distinguishes the female cockroach (_Blatta_) and is more universally
prevalent in that genus than in _Lampyris_, in which a large number
of females have both elytra and wings. The males of _Bombyx antiqua_
and _Gonostigma_, and of many other moths, have wings of the usual
ample dimensions, while those of their females are merely rudiments.
This is the case, also, with some of the _Ichneumonidæ_[840]. In the
tribes of Ants, _Termites_, &c. the neuters or workers are without
wings. Amongst the plant-lice (_Aphides_) there are individuals
of both sexes, some of which have wings, and others not[841].
Amongst the _Coleoptera_, the female of _Tenebrio Molitor_, the
common meal-worm, has elytra and no wings; while the male has
both[842].--Sometimes these organs vary in size in the sexes: thus
in _Aradus Betulæ_ F., a kind of bug, the hemelytra and wings are
narrower and shorter in the female than in the male[843]. In the
genus _Blaps_ F., the mucro that arms the apex of each elytrum is
longer in the former sex than in the latter. In _Ateuchus gibbosus_
F., a dung-beetle, the elytra have a basal gibbosity near the suture
in one sex that does not obtain in the other. In the _Orthoptera_
order, the sexes are often to be known, almost at first sight, by
a difference in the veining and areolets of the wings; but upon
this I enlarged so fully when I treated of the sounds produced by
insects, that it is not necessary to repeat what I have said; which
observation also applies to the drums which distinguish the male
_Cicadæ_[844]. The wings of some butterflies, and of most moths and
hawkmoths (_Sphinx_ L.), are furnished with a singular apparatus for
keeping them steady, and the under-wing from passing over the upper
in flight. This appears to have been first noticed by _Moses Harris_,
and was afterwards more fully explained by _M. Esprit Giorna_[845].
From the base of the under-wing proceeds a strong bristle, received
by an annulus or socket, which springing between the two principal
nervures of the upper-wing terminates in the disk of the wing:
in this annulus the bristle moves to and fro, and prevents the
displacement of the under-wing. This apparatus is perfect only in
the males, which alone have occasion for long flights; the females,
though they have often several bristles, having no annulus[846].
The other instruments of motion, the _legs_, also differ in the
sexes. In some instances they are disproportionably long. This is
particularly the case with the _anterior_ pair of some beetles, as
_Macropus longimanus_, _Scarabæus longimanus_ L., in which they are
so long as to make the males of these individuals rather inconvenient
in a cabinet. Amongst British beetles _Clytra longimana_ and
_Curculio longimanus_ Marsh. are also remarkable in this respect. In
some other males the _middle_ pair are the longest; as in _Anthophora
retusa_ Latr., a kind of wild-bee[847]. There are two known instances
of remarkably long _posterior_ legs in the Capricorn tribe, which
I suspect belong to the present head. One is _Saperda hirtipes_
Oliv.[848], in which the hind-legs are longer than the whole body,
and adorned with a singular tuft of hairs; and the other a _Clytus_,
I think, which Mr. MacLeay purchased from the late Mr. Marsham's
collection, in which the hind-legs are not only very long, but have
tarsi convolute, like some antennæ. From analogy I should affirm that
these were the characters of _male_ insects.
To come to the _parts_ of legs. Sometimes the _coxæ_ of the last
mentioned sex are distinguished from those of the female by
being armed by a _mucro_ or spine. Thus the male of _Megachile
Willughbiella_, and others of that tribe, have such a spine on the
inner sides of the anterior coxa[849]. The _Trochanter_ also of some
differs sexually; and you will find that the posterior one of the
male in _Anthidium manicatum_ is of a different shape from what it is
in the female[850]. In _Sphodrus leucopththalmus_, one of the beetles
called _black dors_, in one sex the same trochanter terminates in a
long mucro or spine[851], and in the other it is rounded at the apex.
Peculiar characters in their _thighs_ also often indicate different
sexes. In _Prionus damicornis_ there is a short spine at the apex of
the _anterior_ ones in the female that is not in the male; while in
_Macropus longimanus_, at their base externally the male is armed
with a mucro, which I cannot find in the female[852]. In _Scarabæus
longimanus_ L. this thigh is furnished with two teeth[853].--The
_intermediate_ thighs also sometimes differ. In an _Onitis_ from
China, a variety perhaps of _O. Sphinx,_ those in the male are
dolabriform, and in the other sex of the ordinary shape. In _Odynerus
spinipes_ they have on their lower side two sinuses, so as to give
them the appearance of being toothed. The _posterior_ thighs are
sometimes incrassated in the male, and not in the female. This you
will see in a weevil, not uncommon, _Apoderus Betulæ,_ and also
in many species of _Cimbex_ F., a kind of saw-fly; and the same
circumstance distinguishes the latter sex in many species of _Lygæus_
F., a kind of bug: I discovered this from _L. cruciger_, of which I
have both the sexes; and from Stoll's figure of _L. Pharaonis_[854].
In some of these the female thighs are enormously large. A remarkable
variation in this respect is observable in the coleopterous genus
_Œdemera_ (_Necydalis_ L.). In _Œ. Podagrariæ_ these limbs are
incrassated in one sex and not in the other[855]; in _Œ. cærulea_
they are so in both sexes; and in _Œ. ceramboides_ in neither. In
_Pelecinus Polycerator_ F., one of the Ichneumon tribe, or an insect
very near it from Brazil, these thighs in the female are armed with
two spines underneath, which are not in the male.
The _anterior tibiæ_ in _Scarabæus longimanus_ L. differ remarkably
in the sexes. In the female they are of the ordinary shape, and
serrated externally; but in the male they are very long, incurved,
and without teeth or serratures[856]. In the males of the genus
_Onitis_ F. they are bent like a bow, and acute at the end; but
in the females they are formed on the common type[857]. In _Hispa
spinipes_ F. they are armed internally with a crooked spine[858].
But the most extraordinary sexual variation of this joint of the
leg may be seen in the male of _Crabro cribarius_ F. and several
other species of the same family, in which these tibiæ are dilated
externally into a concavo-convex plate, or rather have one fixed
to them and part of the thigh, of an irregular and somewhat
angular shape[859], with numerous transparent dots, so as not
badly to resemble a sieve: whence the trivial name of the species.
Rolander, who first described it, fancied that this plate was really
perforated, and that by means of it the animal actually sifted the
pollen; but it is most probably for sexual purposes. In another
species, the plate is ornamented with transparent converging streaks.
In the bee-tribes (_Anthophila_ Latr.) the _posterior_ tibia of
the working sex is generally bigger than the corresponding part in
their more idle partners: this is particularly conspicuous in the
genus _Euglossa_, in the females of which this part is triangular,
very broad towards the apex, and fitted for carrying a large mass
of pollen paste. The tibiæ of the _males_ of some _Lepidoptera_ are
remarkable in this respect. That of _Hepialus Humuli_ is much more
hairy; but in _H. Hectus_ it is a dilated mis-shapen mass, without a
tarsus, and with long scales pendent from the disk[860]. Differences
of this kind also occur in the _calcaria_ or spurs that arm the apex
of the tibiæ of a large number of insects. Thus in _Acanthopus_ Klug,
a singular bee, in the male the spur of the intermediate leg is
dilated at the apex, and armed with six strong spines, the inner one
larger than the rest[861].