ii. The sexes of insects vary (but more rarely than in colour) in

their _sculpture_ also, and _pubescence_. Thus the elytra of the females of many of the larger water-beetles (_Dytiscus_) are deeply furrowed, while those of the males are quite smooth and level[713]. The thorax of the female in several species of _Colymbetes_ of the same tribe, as _C. Hybneri_ and _transversalis_, on each side has several tortuous impressed lines or scratches, like net-work, which are not to be discovered in the male. _Hyphydrus gibbus_ Latr., which differs solely from _H. ovalis_ (_Dytiscus ovalis_ Illig.) in being thickly covered with minute impressed puncta, is, from the observation of the Rev. R. Sheppard, the other sex of this last, with which he has taken it coupled; and it is by no means improbable that _Hydroporus picipes_ (_Dytiscus punctatus_ Marsh.) and _H. lineatus_,--between which, as Gyllenhal has justly observed, the same difference only exists,--are in like manner sexual varieties. With respect to _pubescence_, I have not much to say. Another aquatic beetle, _Acilius sulcatus_ Leach, has not only its elytra sulcated, but the furrows of these, and a transverse one of the thorax, are thickly set with hair; while the male is smooth, and quite naked. Particular care seems to have been taken by the Creator, that when all the above inhabitants of the water are paired, the male should be able to fix himself so firmly, by means of his remarkable anterior tarsi, (which I shall afterwards describe,) and these asperities, &c. in the upper surface of his mate, as not to be displaced by the fluctuations of that element, the reluctance of the coy female, or any other slighter cause.

In a moth called the ghost (_Hepialus Humuli_), the posterior tibia of the male is densely bearded, but not of the female[714].--Some _Hymenoptera_, as _Ammophila_ Kirb. and _Stigmus_ Jurine, have the upper lip of the male clothed with silver pile, while that of the female is not so ornamented. The legs of some bees are distinguished in the sexes by a difference in their _clothing_. That observable in those of the hive-bee has been before noticed[715]. In _Andrena_ of Latreille[716] the posterior tibia of the female is covered externally with a dense brush of hairs, for collecting the pollen; and the posterior legs at their base have a curled lock of hair--which are not to be found in the male[717]. In _Dasypoda_, _Melecta_, _Anthophora_, _Centris_, _Epicharis_, &c. of the same author, the first joint of the tarsus of the female, and in _Xylocopa_ almost the whole tarsus, is also similarly signalized from that of the other sex. In _Bombus_, as in the hive-bee, the posterior tibiæ of the females and neuters are furnished with a basket of hairs for carrying their pollen paste, which you will in vain look for in the male[718]. The latter, however, in some species of this tribe are distinguished from the former by the longer hairs of their legs, but not in the posterior ones. Thus, in _Anthophora retusa_ the first joints of the intermediate tarsus are bearded internally with a thin fringe of long hairs, and the first externally with a triangular one of short ones at the apex: but what is most remarkable, the last or unguicular joint, which in almost every other bee is naked, is on both sides fringed with long hairs[719]. In that remarkable genus _Acanthopus_ Illig., of which the male only is known, the first and last joint of the intermediate tarsus have a dense external brush of stiff hairs, which probably is also a sexual character[720]. Another sexual kind of clothing is exhibited by the females of those bees that have their labrum or upper-lip inflexed (_Megachile_ Latr.)[721]. Their abdomen is covered underneath with a brush of stiff hairs, involved in which they carry the pollen they collect. In the males of some of this tribe, as of _M. Willughbiella_, the first four joints of the anterior tarsus on their inner side have a long dense fringe of incurved hairs[722]: a circumstance also to be found in the same sex of _Xylocopa latipes_, in which the claw-joint also is bearded[723]. In _Andrena_ Latr. the last dorsal segment of the abdomen of the same sex is fringed, while that of the male is naked[724]. In the humble-bees (_Bombus_), the mandibles of the male are bearded with curled hairs, while those of the females and neuters are without them. Some bees, as _Andrena_ and _Halictus_ Latr., have the anus of the female bearded, and that of the male naked: in some _Bombyces_ the reverse takes place.

iii. With regard to the general _shape_ of their body, the male and female usually resemble each other: but there are some exceptions to this rule. The male of the hive-bee is much thicker and more clumsy than either the female or the worker; but in _Halictus_ Latr. the males are nearly cylindrical in shape, and very narrow; while the other sex are oblong or ovate, especially their abdomen: and in _Andrena_ Latr. the former are much slenderer than the females, and of a more lanceolate shape. But a still more striking difference in this respect between the sexes is exhibited by some species of the genus _Ptinus_ F., in which the male is long and slender, and the female short and thick. This, in more than one instance, has occasioned them to be mistaken for distinct insects: thus, _P. Lichenum_ and _P. similis_, _P. ovatus_ and _P. testaceus_, of Mr. Marsham, are mere sexual varieties. But the most entire abalienation of shape at present known, is that which distinguishes the male from the female _Coccus_; these are so completely dissimilar as scarcely to have any part in common. In _Bombyx vestita_ F., and others of the same family, while the males are of the ordinary conformation of the order, the females are without even the slightest rudiments of wings; they have no antennæ, the legs are extremely short, not longer than those of the caterpillar; and the body is entirely destitute of scales, so that they altogether assume the exact appearance of hexapod larvæ[725]. A conformation nearly similar takes place in the female of _Tinea Lichenella_; but in this the feet are longer, and the anus is furnished with a long retractile ovipositor[726].

iv. In many cases, the structure of particular _parts_ and _organs_ of the body differs in the sexes. As the facts connected with this part of our present subject are extremely numerous and various, it will be convenient to subdivide it, and consider the sexual characters that distinguish--the _Head_, _Trunk_, and _Abdomen_ of insects, and their several appendages.

1. The _Head_. This part in some females is considerably larger than it is in the male. This is the case with the ants, and several other _Hymenoptera_; while in some _Andrenæ_, as _A. hæmorrhoidalis_, and _Staphylinidæ_, as _St. olens_, that of the male is the largest. But in none is the difference more conspicuous than in the stag-beetle (_Lucanus_); in which genus the male not only exceeds the female in the length of his mandibles, but also greatly in the size and dimensions of his head. In the _Apion_ genus, the rostrum of the female is generally longer and slenderer than that of her mate; and in _Brentus_, the rostrum of one sex (probably the male) is long and filiform, while in the other it is thick and short. This is particularly visible in _B. dispar_ and _maxillosus_[727], &c.

One of the most striking distinctions of the males in this part of their body, are those threatening horns, usually hollow, with which the heads of many of the male lamellicorn insects and some others are armed, and which give them some resemblance to many of the larger quadrupeds. Many are _unicorns_, and have their head armed with only a _single_ horn; which in some, as in _Oryctes_ Illig., _Dynastes Endymion_[728], &c. is very short; in others, very long, as in _Dynastes Enema_, _Pan_, _Elephas_[729]. In one, again, it is thick and robust; as in the clumsy _Dynastes Actæon_[730]: in another very slender, as in _Onthophagus spinifer_[731]. With respect to its direction in _Elephastomus proboscideus_ MacLeay, it is horizontal[732] and straight; in _Phaleria cornuta_ horizontal and broken, or the apex turning outwards and forming an angle with the base[733]; in _Dynastes Hercules_ horizontal, and recurved at the apex[734]; in _D. Actæon_, _Elephas_, and _Typhon_, recurving from the base. In _Geotrupes dispar_ it is recurved, so that its point exactly coincides with that of the porrected thoracic horn, with which it forms a kind of forceps[735]. In _Copris lunaris_ F. and _Diaperis horrida_, the horn is nearly upright[736]. In _Onthophagus Xiphias_ it is dilated at the base, and reclining upon the thorax; and at the apex attenuated, and bending forwards, or nodding. In _Passalus cornutus_ it rises a little, and then bends wholly forwards. In _Dynastes Milon_, a most remarkable beetle, it slopes backwards in a waving line[737]; and in _Onthophagus spinifer_ it is recurved and reclining.--In speaking of the direction of the horn, you must recollect that it will vary in proportion as the head varies from a horizontal position: so that an upright horn will become inclined or reclined, as the head bends forwards or backwards; but I speak of it as it appears when the head is horizontal. Again, it varies in its teeth or branches. In _Dynastes Hercules_ it is armed with several teeth. In _D. Elephas_ and _Actæon_ it has only one large one at its upper base[738]. In _D. Milon_ it is serrated above. In _D. Alcides_, _Tityus_, _Ægeon_, _Copris lunaris_, &c. the horn is unarmed and simple at the apex. In _D. Oromedon_, _Gedeon_, _Enema_, _Actæon_ and congeners, it is bifid. In some the horn is at first a broad lamina or ridge, which terminates in two branches, as in _Onthophagus Vacca_. In this the branches are straight; but in another undescribed species in my cabinet (_O. Aries_ Kirby, MS.) they are first bent inwards, and then at the apex a little recurved: and in _D. dichotomus_ it is divided into two short branches, each of which is bifid[739]. Other males emulate the bull, the he-goat, or the stag, in having a _pair_ of horns on their head. In _Onthophagus Taurus_, these arms in their curvature exactly resemble those of the first of these animals[740]. In _Goliathus pulverulentus_, the straight, robust, diverging, sharp horns are not unlike those of some of the goat or gazel tribe. I have a beautiful little specimen in my cabinet, (I believe collected by Mr. Abbott of Georgia,) in which the horns have a lateral tooth, or short branch, like those of a stag; and which I have therefore named _O. cervicornis_. In _O. Vacca_, _Camelus_, &c. the horns are very short, and nearly perpendicular. In the male of _Copris Midas_, the two longer perpendicular horns have a deep cavity between them, which, together with its black colour, give it a most demoniac aspect; so that you would think it more aptly representative of a Beelzebub or _Beelzebul_ than a Midas[741], or than _Phanæus Beelzebul_ MacL. A similar cavity is between the occipital horns of _Diaperis hæmorrhoidalis_ Payk. Some species of _Rynchænus_, as _R. Taurus_, have a pair of long horns upon the rostrum of the male, the rudiments only of which are to be traced in the female[742]. Other species go beyond any known quadrupeds in the number of horns that arm their heads. Thus _Ditomus calydonius_ Bonelli, belonging to _Carabus_ L., has _three_ equal horns[743]. The same number distinguishes _Onthophagus Bonasus_; but the intermediate one is very short. In _Goliathus Polyphemus_ the middle horn, on the contrary, is much longer and thicker than the lateral ones, and forked at the apex; so that it looks as if it had four of these weapons[744]. A little _Diaperis_ (_D. viridipennis_ F.), a native of _Carolina_, has four horns upon the head of the male; namely, two long ones on the occiput, and two short dentiform ones on the nose. In a species nearly related to this, sent me by Professor Peck from New England, there is a cavity between the two occipital horns. The same number distinguishes _Onthophagus quadricornis_ (_Copris_ F.). The _situation_ also of the horns varies: In some it is in the _middle_ of the head, as _Oryctes nasicornis_, _Copris lunaris_, &c.: in others, as in _Onthophagus nuchicornis_, _Xiphias_, &c. it is a process of the _occiput_ or hind-head; and in _O. Oryx_ F. the two horns proceed from the _anterior_ part of the head. In the other sex, in insects the head of whose males is armed with horns, they are usually replaced by mere tubercles, or very short elevations, as you may see in the female of _Copris lunaris_; or by transverse ridges, as in the _Onthophagi_: or else the head is without arms, and quite smooth, as in _Diaperis_, _Phaleria_, &c. What may be the use of these extraordinary appendages, as well as those on the thorax, and in some cases on the abdomen, (which I shall mention afterwards), to the males, has not yet been ascertained. Whether the individuals of this sex are more exposed to the attack of birds and other enemies, in consequence of being more on the wing than the females, and are therefore thus provided with numerous projecting points for defence, is a question worth considering[745]. It is the only probable conjecture on the _cui bono_ of these arms that I can at present make. Under this head I ought to notice the remarkable membranous process of an obovate shape, which like an umbrella covers the head of _Acheta umbraculata_ F.[746] Whether the sharp curved horns which arm this part in another _Acheta_ figured by Stoll[747], in an incumbent posture, with their point towards the mouth, are a sexual distinction, we are not informed,--probably they are.

The _organs_ of the head also present many sexual distinctions. The upper lip (_labrum_) in _Halictus_ Latr., a tribe of wild bees, in the female is furnished with an inflexed appendage, which is not discoverable in that of the male[748]; and the shape of this lip in _Sphecodes_ Latr. differs in the sexes[749]. Perhaps the horn or tubercle observable on this part of some female _Nomadæ_ F.[750] may be wanting in the male.

The under-lip (_labium_)--taken in a restricted sense for that central part from which emerge the labial palpi, and which is often considered as the mentum,--does not offer any striking variations in the sexes. One, however, is of importance, as it helps to prove which are the true female _Lucani_. In the male the labium is emarginate, in the female it is intire. This may be seen both in _L. Cervus_ and _femoratus_, and probably in other species. The sculpture also is different, the lip being smooth in the former and covered with excavated _puncta_ in the latter. The tongue (_lingua_ or _ligula_) of the sexes is usually the same; except in the hive-bee, in which that of the neuters is longer than that of the male and female.

The upper-jaws (_mandibulæ_), however, often afford striking sexual characters. The enormous protended ones of the common stag-beetle (_Lucanus Cervus_) attract the attention of the most incurious observer; and these are now generally allowed to be of this description. Geoffroy and Mr. Marsham, indeed, have asserted that they have taken _in coitu_ those with long mandibles: but as these males are pugnacious, and attack each other with great fury, as Mr. Sheppard informs me, it is not improbable that these gentlemen may have mistaken a _battle_ for an _amour_: since not only have those with long mandibles been often taken united with those that have short ones[751], but the same difference obtains in the sexes of other species. This is particularly observable in _Lucanus femoratus_, of which I received from Brazil many specimens agreeing in every respect except in this, that one had short and the other very long mandibles. These organs vary in different specimens, as to the number of their teeth and branches. They are singularly robust in _L. Alces_[752]; but in none more threatening than in _L. Elephas_[753], in which they curve outwards and downwards. In Mr. W. MacLeay's genus _Pholidotus_, they are almost parallel to each other, and curve downwards; in _Lucanus nebulosus_ Kirby, they assume a contrary direction[754]; as they do likewise in _Lamprima_ Latr.[755] In _Lucanus Capreolus_ the points close over each other[756]. In _Lethrus_ F. in the female, but not the male, the mandible is armed below with a long incurved horn. In _Lucanus serricornis_ they form a complete forceps[757]. In _Siagonium quadricorne_ Kirby[758] the mandible is furnished at its base with an exterior horn, which is probably a sexual distinction. The male of _Synagris cornuta_, a kind of wasp, is still more conspicuous in this respect; for from the upper side of the base of its straight slender mandibles proceed a pair of crooked, decurved, tortuous, sharp horns, not only longer than the mandible, but than the head itself[759]. Many sexual differences are observable in the mandibles of the various tribes of bees (_Anthophila_ Latr.). Thus, in _Colletes_ Latr. the _male_ mandible is more distinctly bidentate at the apex than the female[760]: in _Sphecodes_ Latr. and others, the reverse of this takes place[761]. Where these organs in both sexes are toothed at the apex, they often vary in the number of teeth. Thus, the female of _Megachile centuncularis_ Latr. has four teeth at the apex of its mandible, while the male has only two[762]. In _M. Willughbiella_, though the mandibles of both sexes have four teeth, yet those of the male are sharp, and the two external ones the longest; while those of his mate are obtuse, and all nearly equal in length[763]. In _Anthidium manicatum_ Latr., the former has only three teeth, while the latter has five[764]. The differences in this respect in the hive-bee have been before noticed[765]; those of the humble-bees (_Bombus_ Latr.) are strikingly distinguished from each other; the female mandible being very stout and wide, constricted in the middle, and furrowed on its outer surface; and the male, on the contrary, very slender at the apex, dilated at the base, and without furrows[766].

Of all the organs of the head, none seem so little subject to _sexual_ variation as the under-jaws (_maxillæ_)[767]. I can bring forward only one striking instance of it, and some degree of doubt rests even upon that. In the genus _Nemognatha_ of Illiger, the maxillæ of the male are elongated, narrow, setiform, and often involute or spiral, like those of a bee or a butterfly. But that this is peculiar to the males is at present only surmised[768]. I possess several species of the genus, all of which are distinguished by long maxillæ; though in some they are as long as the body, and in others scarcely half that length. _Gnathium_ Kirby is similarly characterized[769].

The _maxillary palpi_ occasionally differ in the sexes. In _Cerocoma_ those of the female are filiform, while the two intermediate joints of those of the other sex are much thicker than the first and the last[770]. In _Hylæcetus_ and _Lymexylon_, those of the male are still more remarkable: they are pendent, the last joint very large, and laciniated so as to form a tuft[771]. The female ones grow gradually larger towards the end, but are not at all divided there[772]. The palpi of male spiders are of a very different structure from those of the other sex, terminating in a very complex incrassated piece, which has been supposed to contain the organ of generation; but this, according to Treviranus, is a mistaken idea--that organ being, as usual, to be found in the abdomen[773]. In the common gnat the palpi of the male are as long as the proboscis, consist of five joints, and at the end are tufted with hairs; while those of the female are scarcely one-fourth of its length, have only three joints, and are not tufted. Whether the _labial palpi_ in any genus differ in the sexes, I cannot affirm with certainty: I have not, however, observed any such variation in them.

I shall next mention some organs of the head, in which the difference between the sexes is often very striking and peculiar. You will readily conjecture that I am speaking of the _antennæ_. And here the advantage seems wholly on the side of the males: since in them these wonderful instruments of unknown sensations are not only more complex, but usually more elegant, than those of the other sex. You will pardon me, therefore, if I enlarge a little more than ordinary upon a subject so full of interest, and say something upon the differences observable between the sexes--in the shape, magnitude, and length, number of articulations, ramification and plumage, and individual joints of their antennæ.

With regard to their _shape_, variations are sometimes observable between the antennæ of the sexes; but this principally occurs in the _Hymenoptera_ order. For instance, those of _Chelostoma maxillosa_, a small bee that deposits its eggs in little holes in posts and rails, are clavate in the female and filiform in the male[774]--a circumstance that distinguishes in some degree those of _Sphecodes_, _Halictus_, and _Andrena_ of Latreille, three other genera of wild-bees[775]. In _Dinetus_ Jur. the male antennæ are moniliform at the base, and filiform at the apex; the female, on the contrary, are entirely filiform[776].

The antennæ of the sexes also sometimes differ in _magnitude_ and _length_. This is the case in the three genera of wild bees just mentioned; those of the female being thicker than those of the male, while these last are longer than the former. But in this tribe the males of the Fabrician genus _Eucera_ are most remarkable for their long antennæ[777]. With regard to the different length of these organs in the sexes, no insects are more distinguished than some species of the capricorn-beetles (_Cerambyx_ L.). In _Lamia Sutor_ the male antennæ are twice the length of the female; and in another Brazilian species in my cabinet, related to _L. annulata_ (_Stenocorus_ F.), they are thrice their length. Some of the _Anthribi_ F. approach the _Cerambycidæ_, not only in some other characters, but also in this circumstance:--thus the antennæ of _A. albinus_, a native of Britain, are vastly longer in the male than in the female; and in _A. cinereus_ (_Macrocephalus_ Oliv.)[778], which I suspect to be of the former sex, they are as long nearly as is usual in the tribe just named, called in France capricorn-beetles.

I may here observe, that sometimes in the sexes a difference is also to be found in the _direction_ or flexure of their antennæ. Thus in _Scolia_ F., _Pepsis_ F. &c., in the males the antennæ are nearly straight, but in the females convolute or subspiral. The reverse of this takes place in _Epipone spinipes_, a kind of wasp, and its affinities; and _Systropha_ Illig., a kind of bee: for in these the male antenna is convolute at the apex[779], and the female straight. In the various tribes of bees (_Anthophila_ Latr.), these organs in the latter are what is denominated _broken_, the main body of the antenna forming an angle with the first joints: but in the former this does not take place.

The antennas of the sexes do not always agree in the _number_ of joints. In the bees, and many other _Hymenoptera_, the male has one more joint than the female; as is the case also in _Œdemera notata_ (_Cantharis acuta_ Marsh.). In _Pteronus Laricis_, a kind of saw-fly, the latter has only sixteen joints in its antennæ, while the former has twenty-four[780]. In _Rhipicera marginata_, a beetle, the beautiful antennæ of the male consist of thirty-two joints, while the female has no more than eleven! In _Chelonus_ Jur. the male, on the contrary, has the smallest number of joints, namely sixteen; while the female has twenty-five[781].

In nothing do the sexes differ more materially than in the _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].

But the part of the leg in which the sexes most vary is the _tarsus_; and this variation takes place both in the number of the joints, and their form and circumstances. The first case has been observed only with regard to certain species of _Cryptophagus_ Herbst, as _C. fumatus_, &c. in which the female is _pentamerous_, or having _five_ joints in all the tarsi; and the male _heteromerous_, or having _five_ joints in the two _anterior_ pairs, and only _four_ in the _posterior_[862]. With respect to the form of the tarsal joints, the sexes more frequently differ; and by inspecting this part, especially in the predaceous and carnivorous _Coleoptera_, you may often, without further examination, ascertain whether any individual is male or female. Even in the slender-footed _Cicindelidæ_, the three first joints of the anterior tarsus of the male are more dilated than the two last, and covered underneath with a brush of stiffish hair; in the female all are equally slender, and not so hairy. In _Carabus_, _Feronia_, &c. Latr. the _four_ first joints of these tarsi in the males are dilated, and furnished with a brush or cushion: in the _Silphidæ_, also, the same circumstance takes place. In _Harpalus_ Latr., and _Silpha americana_, the _four_ anterior ones are similarly formed in this respect. But one of the most remarkable sexual characters, in this tribe of insects, that distinguish the males, are those orbicular patellæ, furnished below with suckers of various sizes, and formed by the three first joints of the tarsus, which are to be met with in the _Dytiscidæ_, &c.; but as I shall have occasion to treat of these more fully in another Letter, I shall only allude to them now. The second pair of tarsi have in these also the three first joints dilated and cushioned[863]. In _Hydrophilus piceus_, another water-beetle, the fifth joint of the tarsus is dilated externally, so as to form nearly an equilateral triangle[864]. Christian, a German writer on the _Hymenoptera_, has described some very singular appendages which he observed on the first joint of the four posterior tarsi of _Xylocopa latipes_ F. These were battledore-shaped membranaceous laminæ, with a reticulated surface, of a pale colour; which were fixed in pairs by the intervention of a footstalk to the above joint, on which they sometimes amounted to more than a hundred: the use of which, he conjectures, is the collection of pollen[865]. I possess two specimens of this bee; one has none of these appendages, and on the other I can discover them only in one of the tarsi--from which circumstance I am led to conjecture that, like the supposed _Clavariæ_ that were imagined to grow on some humble-bees, but which are now ascertained to be the anthers of flowers--these also belong to the kingdom of Flora, and are spoils which the bee in question has filched from the blossom of some plant. The individuals that have been thus circumstanced are males; whether the female is guilty of similar spoliations is not known. In my specimen there are no traces of them. In many bees, the first joint of the posterior tarsi is much larger in the females and workers than in the males; but in the hive-bee this joint is largest in the latter[866]. In _Beris clavipes_ and _Empis nigra_, two flies, the joint in question is large and thick in the male, but slender in the female. The penultimate tarsal joint in the posterior legs is dilated internally, and terminates in a mucro in one sex of _Anoplognathus Dytiscoides_ of Mr. W. MacLeay[867]. In some insects the anterior tarsus of the males has been supposed to be altogether wanting: I allude to the petalocerous genus _Onitis_ F.; but I have a specimen of _Onitis Apelles_ of this sex, or a species nearly related to it, in which one of these tarsi is to be found[868]; which, though very slender, consists of five joints, and is armed with a double claw: from which circumstance it may, I think, be concluded, that although, as in _Phanæus_, these tarsi are very minute, they are not wanting. What renders this more probable is, a circumstance which every collector of insects, who has many specimens of Mr. W. MacLeay's _Scarabæidæ_ in his cabinet, must have noticed: namely, that in all, except _Copris_ and _Onthophagus_, the anterior tarsi are usually broken off. Out of seventeen individuals of _Scarabæus_ MacLeay in my own, not a single one has a relic of an anterior tarsus; and scarcely one in a much greater number of _Phanæi_. The tarsus in question in the nobler sex in _Crabro_, at least in _C. cribrarius_ and its affinities, is also very short, especially the three intermediate joints; but at the same time very broad and flat. In the species just named, the external claw forms a kind of hook; and in the rest it is considerably longer than the other[869]. The _claws_, indeed, occasionally vary in the sexes in other _Hymenoptera_: thus in _Melecta_ Latr., a kind of bee, in the female they are intire, but in the male they are furnished with an internal submembranaceous tooth or process[870]. In _Cœlioxys conica_ and others, those of the latter sex are bifid at the apex, but those of the former acute[871]. In _Megachile_, the male claw is as in the instance just mentioned, while the female has a lateral tooth[872]; and a similar character distinguishes the sexes in the hive-bee[873].

3. The _abdomen_. This part affords many external sexual characters, whether we consider its general shape; the number of segments that compose it; its base, middle, or extremity.

In general _shape_ it often differs in the sexes. Thus, the abdomen of female _Tipulæ_ is lanceolate; that of the male cylindrical, and thickest at the extremity[874]. In _Molorchus_ F. it is convex above in the former, and flat in the latter,--the female of this beetle not unaptly representing some female _Ichneumons_ in this respect, and the male their males[875]. In _Andrena_ it is oblong in the one, and lanceolate in the other. In the hive-bee the drones have a thick, obtuse, and rather long abdomen; in the females it is long, and nearly represents an inverted cone; and in the workers a three-sided figure, or prism.

The _number of segments_, also, is generally different in the two sexes--the male having one more than the female; but in _Dytiscus marginalis_, &c. the reverse of this takes place: the female, if you reckon the bipartite half-concealed anal segment as one, having seven ventral segments, and the male only six. She has also eight dorsal, and the male seven.--In the ant tribes (_Formica_ L.), the little vertical scale, at the _base_ of the abdomen in one description of them, or the double knot in another, is less in the male than in the female. In a very singular male insect belonging to the _Vespidæ_, and related to _Synagris_, (which I purchased from the late Mr. Drury's cabinet,) the second ventral segment sends forth from its disk two remarkable parallel very acute and rather long spines. The same sex of _Chelostoma maxillosa_ has likewise on the same segment a concave elevation, opposite to which on the fifth is a cavity which receives it, when the animal rolls itself up to take its repose[876]. In another species, _C. Campanularum_, the segment in question has only a tubercle[877].

On the second segment of the abdomen of some specimens, probably males, of the remarkable African genus _Pneumora_ before alluded to[878], there are thirteen little elevated ridges, placed rather obliquely in an oblique series; and gradually, though slightly, diminishing in size towards the belly: on their upper side they are flat, forming nearly a horizontal ledge, but on the lower they slope to the abdomen. The posterior thigh in its natural position covers the three first of them, and, if moved downwards, would strike them all[879]. I conjecture, therefore, that these are the animal's instruments of sound, imitating the harp or violin rather than the drum; and that the thigh acts the part of the hand or bow. The abdomen of these insects being blown out like a bladder, and almost empty[880], must emit a considerable sound when the thigh of the animal passes briskly over these ridges; and their different length would produce a modulation in the sound. When struck with a pin, they emit a grating noise.

In _Staphylinus splendens_, the _penultimate_ ventral segment is very deeply cleft, and the antepenultimate emarginate in one sex, and intire in the other. In _S. laminatus_, an allied species, the penultimate segment is cleft, less deeply, however; but the antepenultimate is very short and intire; while the fourth is extremely long, and rounded at the margin, appearing as if it was only an elevated part of the last-mentioned segment; for which it was mistaken by Gravenhorst[881], while it is of the usual form in the other sex.

The _extremity_ of the abdomen or its _anal_ segments and organs furnish a variety of sexual characters. Sometimes the last dorsal segment is emarginate in the male, and not in the female; as in _Megachile ligniseca_, one of the leaf-cutter bees, _Cimex hæmorrhoidalis_, &c.[882] At other times little lateral teeth are added to this notch, as in another of the same tribe, _M. Willughbiella_[883]. Again, in other males, both the ventral and dorsal anal segment are armed each with a pair of teeth or mucros, as in _Chelostoma maxillosa_[884]. In _Anthidium manicatum_, another bee, the anus terminates in five spines[885]. In _Cœlioxys conica_ of the same tribe, in which this part in the female is very acute, that of the male is armed with six points[886]. In that singular Neuropterous genus _Panorpa_, while the abdomen of the female is of the ordinary form, with a pair of biarticulate palpiform organs attached to the last retractile joint, or ovipositor, that of the male terminates in a jointed tail, not unlike a scorpion's, at the end of which is an incrassated joint armed with a forceps[887]. In the common earwig (_Forficula auricularia_) the two sexes differ considerably in their anal forceps: in one it is armed with internal teeth at the base, and suddenly dilated, above which dilatation it is bent like a bow: in the other it is smaller, without teeth, grows gradually narrower, is very minutely crenulate from the base to the end, and is straight, except at the very summit, where it curves inwards. Misled by these and similar differences, Mr. Marsham has considered them (the sexes both of _F. auricularia_ and _F. minor_) as distinct species.

The tail of some species of the genus _Ephemera_ is furnished with three long, jointed, hairy bristles. We learn from Reaumur with respect to one, that though in the female these are all equal in length, yet in the male there is only a rudiment of the third. On the belly near the anus these males have four fleshy appendages, the posterior ones setaceous and long, and the anterior pair filiform and shorter. They are supposed to represent the anal forceps of other insects[888]. In _Ephemera vulgata_, described by De Geer, both sexes have three bristles, but those of the male are the longest; and he describes the forceps as consisting of only a pair of jointed pieces, forming a bow not unlike the forceps of an earwig[889].