i. Manitruncus (the Manitrunk). The anterior segment of the trunk, in which the head inosculates, or on which it turns[998]. It includes the Prothorax and Antepectus.
1. Prothorax (the Prothorax). The upper part or the shield of the manitrunk, in Coleoptera, Orthoptera, &c. called by way of eminence the Thorax[999]. It includes the Ora, Patagia, Umbones, and Phragma.
A Ora (the Ora). The inflexed or inferior lateral margin of the Prothorax, separated in many genera from the Antepectus by a suture[1000].
B Patagia (the Patagia). Two corneous scales observable in Lepidoptera, fixed on each side of the trunk, just behind the head, and covered with a long tuft of hair[1001].
C Umbones (the Bosses). Two moveable bosses surmounted by a spine, with which the Prothorax of the Coleopterous genus Macropus is armed.
D Phragma (the Phragm). The Septum that closes the posterior orifice of the Prothorax in Gryllotalpa Latr.
2. Antepectus (the Forebreast). The underside or breastplate of the manitrunk, and the bed of the Arms[1002]. It includes the Spiracula Antepectoralia, Prosternum, Antefurca, and Brachia.
A Spiracula Antepectoralia (the Antepectoral Spiracles). A pair of breathing-pores fixed in the membrane that connects the Antepectus with the Medipectus[1003].
B Prosternum (the Forebreast-bone). A longitudinal or other elevation of the Antepectus between the Brachia[1004].
C Antefurca (the Antefurca). An internal vertical process of the Antepectus, consisting usually of two branches, which afford a point of attachment to muscles of the Brachia[1005].
D Brachia (the Arms). The first pair of legs of Hexapods, the direction of which is usually towards the head; when spoken of with the other legs, called the Forelegs[1006]. They include the Clavicula, Scapula, Humerus, Cubitus, and Manus.
a Clavicula (the Clavicle). The first joint of the Brachium, answering to the Coxa in the legs.
b Scapula (the Scapula). The second joint of the Brachium, answering to the Trochanter in the legs.
c Humerus (the Humerus). The third and elongated joint of the Brachium, answering to the Femur in the legs.
d Cubitus (the Cubitus). The fourth and elongated joint, answering to the Tibia in the legs. It includes the Coronula and Calcaria. . A Coronula (the Coronula). A coronet or semicoronet of spines, observable at the apex of the Cubitus or Tibia of some insects.—Ex. Dilophus Latr., Fulgora L.
B Calcaria (the Spurs). See the definition under Pedes Postici. They include the Velum.
a Velum (the Velum). A membrane attached to the inner side of the cubital spur in Apis L.[1007]
e Manus (the Hand). The terminal jointed portion of the Brachium, answering to the Tarsus in the legs[1008]. It includes the Pulvilli, Palma, and Digitus.
f Pulvilli (the Pulvilli). See definition under Pedes Postici.
g Palma (the Palm). The first joint of the Manus, when longer and broader than the subsequent ones, or otherwise remarkable; answering to the Planta in the legs[1009].
A Digitus (the Finger). See definition under Pedes Postici. It includes the Ungula.
a Ungula (the Claw-joint). See definition under Pedes Postici. It includes the Pollex, Unguiculi, and Palmula.
α Pollex (the Thumb). A small accessory joint, attached to the Ungula of the Manus in Mantis F.
β Unguiculi (the Claws). See definition under Pedes Postici.
γ Palmula (the Palmlet). A minute accessory joint between the claws, answering to the Plantula in the legs. It includes the Pseudonychia.
* Pseudonychia (the Spurious Claws). See definition under Pedes Postici.
ii. Alitruncus (the Alitrunk). The posterior segment of the trunk to which the abdomen is affixed, and which bears the legs and wings[1010]. It includes the Mesothorax and Medipectus, and the Metathorax and Postpectus.
1. Mesothorax (the Mesothorax). That segment of the alitrunk which bears the Elytra, or the anterior pair of wings, and the intermediate pair of legs[1011]. It includes the Collare, Prophragma, Dorsolum, Scutellum, Frænum, and Pnystega.
A Collare (the Collar). The first or anterior piece of the Mesothorax. In most insects that have a conspicuous Prothorax, as the Coleoptera, this piece appears scarcely to have a representative; but in the Libellulina it co-exists with it, and is more conspicuous[1012]. It is particularly remarkable in Hymenoptera and Diptera.
B Prophragma (the Prophragm). A partition of an elastic substance, rather horny, connected posteriorly with the Dorsolum, which passes down into the anterior cavity of the alitrunk, of which it forms the upper separation from that of the manitrunk. It affords a point of attachment to several muscles of the wings, &c.[1013]
C Dorsolum (the Dorslet). The piece which lies between the Collare and Scutellum, to which the prophragm is anteriorly attached, and which bears the upper or anterior organs of flight[1014]. It includes the Pteropega, Elytra, Tegmina, Hemelytra, Alæ Superiores, and Tegulæ.
a Pteropega (the Wing-socket). The space in which the organs for flight are planted. That for the secondary or under-wings is in the Metathorax[1015].
b Elytra (the Elytra). The upper organs for flight, when they are without nervures, and uniformly of a thicker harder substance than membrane whether corneous, or coriaceous; lined by a fine membrane; and when closed, united by the longitudinal suture[1016]. They include the Axis, Sutura, Epipleura, Alula, and Hypoderma, and are peculiar to the Coleoptera and Dermaptera.
A Axis (the Axis). A small, prominent, irregular process of the base of the Elytrum, upon which it turns, and by the intervention of which it is affixed to the Dorsolum, in the anterior wing-socket[1017].
B Sutura (the Suture). The conflux of the sutural or inner margins of the two Elytra, where when closed they unite longitudinally[1018].
C Epipleura (the Epipleura). The inflexed accessory margin observable underneath in many Elytra, which covers the sides of the alitrunk and abdomen[1019].
D Alula (the Winglet). A small, membranous, wing-like appendage, attached to the Elytrum on one side and the Frænum on the other; which probably serves to prevent the dislocation of the former[1020].—Ex. Dytiscus. N. B. A similar organ for a similar purpose is to be found in Blatta and the Diptera.
E Hypoderma (the Hypoderma). The skin, in some species beautifully coloured, that lines the Elytra[1021]. N. B. This skin is also found in some Hemelytra, but not in Tegmina.
c Tegmina (the Tegmina). The upper organs of flight, when of a uniform coriaceous or pergameneous texture, veined with nervures, and lapping over each other[1022]. Ex. Orthoptera[1023].
d Hemelytra (the Hemelytra). The upper organs of flight, when they are corneous or coriaceous at the base and membranous at the apex[1024].—Ex. The heteropterous Hemiptera. They include the Corium and Membrana.
A Corium (the Corium). The corneous or coriaceous part of the Hemelytrum[1025].
B Membrana (the Membrane). The membranous part of the same[1026].
e Alæ Superiores vel Primariæ (the Upper or Primary Wings). The upper or anterior organs of flight when formed of membrane, or of the same substance with the under-wings[1027]. They include the Axes, Areæ, Areolæ, Neuræ, Stigma, Parastigma, and Lobuli.
A Axes (the Axes). Several osseous or horny pieces, by which the wing is connected with the Dorsolum[1028]. One usually to each area.
B Areæ (the Areas). The larger longitudinal spaces into which the wing may be divided[1029]. They include the Area Costalis, Intermedia, and Analis.
a Area Costalis (the Costal Area). That part of the wing lying between the anterior margin and the post-costal nervure[1030]. In Hymenoptera and Diptera it includes all the space bounded by the nervures that spring from the postcostal.
b Area Intermedia (the Intermediate Area). That part of the wing lying between the costal area and the interno-medial nervure, in Diptera; or the Anal in Orthoptera, Hemiptera, Hymenoptera, &c.[1031]
c Area Analis (the Anal Area). All that part of the wing which in Diptera lies between the internomedial nervure; or in Orthoptera, &c. between the anal nervure and the posterior margin[1032].
C Areolæ (the Areolets). The smaller spaces into which the wing is divided by the nervures. They include the Areolæ Basilares, Mediæ, and Apicales.
a Areolæ Basilares (the Basal Areolets). The parallel areolets of the base of the wing[1033].
b Areolæ Mediæ (the Middle Areolets). The areolets of the wing that lie between the basal areolets and the apical[1034].
c Areolæ Apicales (the Apical Areolets). Those areolets of the wing that terminate in or very near the apex[1035].
D Neuræ (the Nervures). Corneous tubes, for expanding the wing and keeping it tense, and to afford protection to the air-vessels—commonly called the Nerves. They include the Neura Costalis, Postcostalis, Mediastina, Externo-media, Interno-media, Analis, Axillaris, and Spuria.
a Neura Costalis (the Costal Nervure). The first principal nervure of the wing, close to or forming the anterior margin in Lepidoptera, Hymenoptera, and Diptera; but sometimes remote from it in Tegmina[1036]. It includes the Phialum and Hamus.
α Phialum (the Phial). A little bag to receive fluid at the will of the insect, by which the weight of the wing is increased. It is found also in the under-wings in Coleoptera[1037].
β Hamus (the Hook). A Hook fixed to the Costal Nervure, near its base on the under-side, in the wings of some Lepidoptera, in which the tendon runs[1038].
b Neura Postcostalis (the Postcostal Nervure). The second principal, and often strongest, nervure of the wing[1039]. It includes the Neuræ Subcostales.
α Neuræ Subcostales (the Subcostal Nervures). Nervures springing from the under-side of the postcostal nervure, or from each other; called the first, second, third, &c. in the order of their occurrence[1040].
c Neura Mediastina (Mediastinal Nervure). A usually slender nervure, springing from near the base of the postcostal; between which and the costal it intervenes. In the Lepidoptera Diurna, however, it is often a strong nervure[1041].
d Neura Externo-media (the Externo-medial Nervure). The third principal nervure of the wing[1042]. It includes the Neura Subexterno-media.
α Neura Subexterno-media (the Subexterno-medial Nervure). A nervure that in some cases intervenes between the externo-medial and interno-medial[1043].
e Neura Interno-media (the Interno-medial Nervure). The fourth principal nervure[1044]. It includes the Neura Subinterno-media.
α Neura Subinterno-media (the Subinterno-medial Nervure). A nervure that sometimes intervenes between the externo-medial and the anal[1045].
f Neura Analis (the Anal Nervure). The principal nervure nearest the interior or posterior margin, with which it includes a space often subtriangular, traversed in most Diptera and many Hymenoptera by another nervure; and in many Tegmina and Hemelytra by several[1046]. In these kinds of upper-wing it is in many cases accompanied by a fold; and the part between it and the interior margin seems often capable of separate motion.
g Neura Axillaris (the Axillary Nervure). The short nervure, where there is only one, intervening between the anal nervure and the interior margin; replaced in some Muscidæ by a spurious nervure[1047].
h Neuræ Spuriæ (the Spurious Nervures). Very obsolete nervures, sometimes found in addition to those usually occurring; as in Syrphus[1048].
E Stigma (the Stigma). A corneous spot or plate, supposed to contain fluid, in the anterior margin of the upper wings; often produced by the conflux of the costal and postcostal nervures[1049].
F Parastigma (the Parastigma). A corneous spot between the costal and postcostal nervures, distinct from the Stigma observable in the Libellulina.
G Lobuli (Lobuli). One or more rounded portions of the base of the wing, separated from the rest by fissures peculiar to the Muscidæ, and the under-wings of some Hymenoptera[1050].
f Tegulæ (the Tegulæ). Small corneous concavo-convex scales, which in many Orders, particularly Hymenoptera, cover and defend the base of the Upper-Wings[1051].
D Scutellum (the Scutellum). A piece, usually triangular, which follows the Dorsolum; and in Coleoptera is often only a continuation of it—placed between the base of the Elytra or upper-wings[1052].
E Frænum (the Frænum). A piece that lies under the lateral margin of the Scutellum and Dorsolum, or is adjacent to it; and which in many cases connects with the base of the upper organs of flight, so as to prevent their dislocation, by being pushed too far outwards[1053].
F Pnystega (the Pnystega). A corneous scale or plate, which covers certain pneumatic vessels, usually supported by the Scapularia, in Libellulina, &c. becoming dorsal[1054].
2. Medipectus (the Mid-breast). The underside of the first segment of the alitrunk[1055]. It includes the Peristethium, Scapularia, Mesosternum, Medifurca, and Pedes Intermedii.
A Peristethium (the Peristethium). The anterior piece of the Medipectus, which intervenes between the Brachia and mid-legs[1056].
B Scapularia (the Scapulars). Two pieces, one on each side the Medipectus, which succeed the Peristethium, and lie between the midlegs and the Pteropega or wing-socket[1057]. It includes the Spiracula Scapularia.
a. Spiracula Scapularia (the Scapular Spiracles). Two spiracles observable, one in each scapular, in Acrida laurifolia, &c.
C Mesosternum (the Mid-breastbone). The elevated and central part of the Medipectus, between the midlegs, often terminating anteriorly in a mucro; sometimes, as in Elater, in a cavity, receiving the mucro of the Prosternum[1058].
D Medifurca (the Medifurca). A branching vertical process of the Endosternum, which serves as the point of attachment to the muscles that move the midlegs[1059].
E Pedes Intermedii (the Mid-legs). The intermediate pair of legs, consisting of the same parts as the posterior legs[1060].
3. Metathorax (the Metathorax). The posterior segment of the Alitruncus[1061]. It includes the Mesophragma, Postdorsolum, Postscutellum, Postfrænum, Pleuræ, and Metaphragma.
a Mesophragma (the Mesophragm). A partition of a firm consistence, connected by its posterior margin with the Postdorsolum, and passing down vertically into the mid-chest; serving as a point of attachment to several of the muscles that move the wings[1062]. This, with the prophragm, forms the anterior cavity of the alitrunk, and with the metaphragm it forms the posterior cavity.
b Postdorsolum (the Postdorsolum). The middle-piece between the mesophragm and the Postscutellum. In Coleoptera it consists of a tense elastic membrane, which is quite covered by the Mesothorax[1063].
c Postscutellum (the Postscutellum). A narrow channel running from the Dorsolum to the Abdomen in Coleoptera, forming an isosceles triangle reversed. In other orders it is either a triangular elevation of the middle of the posterior part of the Postdorsolum, or a distinct triangular piece[1064].
d Postfrænum (the Postfrænum). In Coleoptera the part of the Metathorax in which the Postscutellum lies, at first nearly horizontal, but posteriorly it takes a vertical direction towards the abdomen. In general it may be defined, the part that intervenes between the Postscutellum and the Abdomen; and which in many cases is connected with the posterior basal margin of the under-wings, and prevents their being pushed too far forwards[1065].
e Pleuræ (the Pleuræ). The space behind the scapulars, on which the lower organs of flight are fixed[1066]. They include the Alæ Inferiores.
A Alæ Inferiores (the Under-wings). The lower or secondary pair of organs for flight[1067]. They include the Commissura, Tendo, Hamuli, Pterygium, Alula, and Halteres.
a Commissura (the Commissura). A joint in the costal nervure of the wings of Coleoptera, where they bend to take a transverse fold[1068].
b Tendo (the Tendon). A strong bristle, or bristles observable at the base underneath in the under-wings of many Lepidoptera, which plays in the Hamus of the upper-wings[1069].
c Hamuli (the Hooklets). Very minute hooks in the middle of the anterior margin, observable in some Hymenoptera, by which the under-wing is fixed to the upper, to cause both to act as one organ in flight[1070].
d Pterygium (the Pterygium). In under-wings this is a small wing-like appendage, fixed at the base of the wing in some Lepidoptera[1071].
e Alula (the Winglet). A small concavo-convex scarious appendage, fixed behind the wings at their base, in many Diptera[1072].
f Halteres (the Poisers). Small capitate processes or organs, observable under the wings of Diptera, attended by a spiracle[1073].
B Metapnystega (the Metapnystega). A corneous scale or lamina that covers the pneumatic organs in the Metathorax, situated sometimes in the Pleuræ, as in the Coleoptera; at others in the Postfrænum, as in Tenthredo L.; and sometimes, as in the Libellulina, between that part and the abdomen[1074].
C Metaphragma (the Metaphragm). A nearly vertical septum or partition, attached behind to the Postfrænum, and usually deeply cleft at its apex in Coleoptera, of a rather horny consistence, which forms the upper separation of the second cavity of the Alitrunk from that of the Abdomen[1075]. It affords a point of attachment for many muscles of both alitrunk and abdomen. It includes the Septula.
a Septula (the Septula). The lesser ridges and partitions raised on the surfaces of the metaphragm, and on those of other parts of the cavities of the trunk, serving as points of attachment to various muscles[1076].
4. Postpectus (the Postpectus). The underside of the second segment of the alitrunk[1077]. It includes the Mesostethium, Parapleuræ, Metasternum, Postfurca, Opercula, and Pedes Postici.
A Mesostethium (the Mesostethium). A central piece between the intermediate and posterior legs, and bounded laterally in Coleoptera by the Parapleuræ—along the middle of which, where it exists, the Metasternum runs[1078].
B Parapleuræ (the Parapleuræ). Two pieces, one on each side of the Postpectus, included between the Scapularia, Mesostethium, and Pleuræ[1079]. They include the Spiracula Parapleuritica.
a Spiracula Parapleuritica (the Parapleuritic Spiracles). Two spiracles, one in each of the Parapleuræ of Tetyra[1080].
C Metasternum (the Metasternum). The central and often elevated part of the Mesostethium. Its anterior mucro, in Coleoptera, often meets the posterior one of the Mesosternum, and sometimes appears to form one piece with it, as in Hydrophilus, and many Lamellicorn beetles. Sometimes, as in Cetonia vitticollis, it even passes between the arms, and covers the Prosternum, or supplies its place. Behind, it often terminates in a bifid mucro. It is not present in many Orders: as in the Hymenoptera, Diptera, &c.[1081] It includes the Pectines.
a Pectines (the Pectines). Two moveable processes, fixed one on each side by its base below the posterior legs to the Metasternum in Scorpio: on the lower side is fixed a series of parallel biarticulate processes, resembling the teeth of a comb[1082].
D Postfurca (the Postfurca). A process of the Endosternum, terminating in three subhorizontal acute branches, resembling the letter Y, and forming an acute angle with the Endosternum, to which the muscles that move the hind-legs, &c. are affixed[1083].
E Opercula (the Opercula). Plates that cover the vocal spiracles in humming insects; and likewise two large cartilaginous plates fixed to the posterior part of the Postpectus, which cover the Tympana in male Tettigonia F.[1084] Perhaps these may be regarded as a kind of Metapnystega in a new situation.
F Pedes Postici (the Hind-legs). The pair of legs affixed to the postpectus[1085]. They include, the Acetabulum, Coxa, Trochanter, Femur, Tibia, and Tarsus.
a Acetabulum (the Socket). The socket in the Postpectus in which the leg is planted[1086]. It includes the Pessella.
A Pessella (the Pessella). Two little acute processes, fixed one in each, in the socket of the hind-legs in male Tettigoniæ, which appear designed to keep down the Opercula[1087].
b Coxa (the Hip). The first joint of the leg which plays in the socket[1088].
c Trochanter (the Trochanter). The second joint of the leg, by which the thigh inosculates in the Coxa. It appears to have no motion separate from that of the thigh. It is sometimes biarticulate[1089].
d Femur (the Thigh). The third joint of the leg, long and usually compressed[1090]. It includes the Gonytheca.
A Gonytheca (the Knee-pan). A concavity at the apex of the thigh, underneath, to receive the base of the Tibia[1091].
e Tibia (the Shank). The fourth joint of the leg, very long, and usually triquetrous[1092]. It includes the Epicnemis, Molula, Talus, Calcaria, and Coronula.
A Epicnemis (the Epicnemis). An accessory joint at the base of the Tibia in many Arachnida, which does not appear to have separate motion[1093].
B Molula (the Knee-ball). The convex and sometimes bent head of the Tibia, armed with a horny process on each side, by which it is attached to the thigh[1094].
C Talus (the Ankle). The apex of the Tibia, where it is united to the Tarsus[1095].
D Calcaria (the Spurs). One, two, or more moveable spines, inserted usually at the apex of the Tibia; and in many Carabi L., Lepidoptera L., and Trichoptera K., in the middle also. They may be regarded as a kind of fingers auxiliary to the Tarsus, and furnish often an important character in the discrimination of genera[1096].
E Coronula (the Coronula). A coronet or semicoronet of fixed spines observable at the apex of the posterior Tibia in Fulgora candelaria, &c.
f Tarsus (the Tarsus). The fifth principal portion of the legs; consisting in the majority of insects of 1-5 joints, but in the Phalangidæ of sometimes as many as 50[1097]. It includes the Planta, Digitus, and Solea.
A Planta (the Instep). The first joint of the Tarsus is so called when it is remarkably long and broad[1098]. It includes the Calx.
a Calx (the Heel). The curving part of the Planta, by which it inosculates with the Tibia.
B Digitus (the Toe). The remaining joints of the Tarsus taken together[1099]. It includes the Allux and Ungula.
a Allux (the Toe-ball). The last joint but one of the Tarsus, when remarkable, as in Rhyncophorous beetles (Curculio L.)[1100].
b Ungula (the Claw-joint). The last joint of the Tarsus, which bears the claws[1101]. It includes the Arthrium, Unguiculi, and Plantula.
α Arthrium (the Arthrium). A very minute joint at the base of the claw-joint, in most Tetramerous and Trimerous beetles[1102].
β Unguiculi (the Claws). One or two pair of moveable incurved claws, which usually arm the apex of the Ungula[1103].
γ Plantula (the Plantula). A minute accessory joint, sometimes attached within the claws to the apex of the Ungula[1104]. Ex. The Lucanidæ. It includes the Pseudonychia.
* Pseudonychia (the Spurious Claws). Two stiff clawlike bristles, that terminate the Plantula[1105].
C Solea (the Sole). The underside of the Tarsus[1106]. It includes the Pulvilli.
a Pulvilli (the Pulvilli). Cushions of short hairs very closely set; or of membrane, capable of being inflated, or very soft; or concave plates, which cover the underside, or their apex, of the four first joints of the Manus or Tarsus, and sometimes even of the ends of the Calcaria, as in Cimbex; which act so as to produce a vacuum, and enable the animal to suspend itself, or walk against gravity[1107]. Ex. Timarcha, Buprestis, Priocera K., the Gryllina, Muscidæ, &c.
III. ABDOMEN (the Abdomen).
The Abdomen is the third or posterior section of the body which follows the Truncus[1108]. It includes the Tergum, Venter, Petiolus, Cauda, and Anus.
i. Tergum (the Tergum). The upper or supine surface of the abdomen[1109]. It includes the Segmenta Dorsalia, and Pulmonaria.
1. Segmenta Dorsalia (the Dorsal Segments). Transverse segments of the back, the sides of which often lap over and cover those of the ventral segments[1110].
2. Pulmonaria (the Pulmonary Space). Two longitudinal soft spaces, capable of tension and relaxation, one on each side of the back of the abdomen, in which, where they exist, the dorsal spiracles are planted[1111]. They include the Spiracula Dorsalia.
a Spiracula Dorsalia (the Dorsal Spiracles). Lateral breathing-pores observable in the dorsal segments, often covered by the preceding segment[1112].
ii. Venter (the Belly). The lower or prone part of the abdomen[1113]. It includes the Hypochondria, Epigastrium[1114], Segmenta Ventralia, and Elastes.
1. Hypochondria (the Hypochondria). Two portions of segments, one on each side; which in some genera[1115] (Carabus L., &c.) intervene between the first intire ventral segment and the posterior part of the Postpectus.
2. Epigastrium (the Epigastrium). The first intire ventral segment[1116]. It includes the Mucro and Tympana.
A Mucro (the Mucro). The central posterior point of the Epigastrium observable in many of the Orders, which reposes between the posterior legs; and, according to M. Chabrier, is useful to the insect during flight[1117].
B Tympana (the Drums). Two deep cavities, containing a complex machinery on each side of the Epigastrium in male Tettigoniæ, which are the instruments of sound[1118].
3. Segmenta Ventralia (the Ventral Segments). Transverse sections of the belly[1119]. In Elytrophorous insects they are usually of a firmer consistence than those of the back. They include the Spiracula Ventralia.
A Spiracula Ventralia (the Ventral Spiracles).—Breathing-pores observable in some genera in the intermediate ventral segments, one on each side[1120]. Ex. Dynastes Aloeus, &c.
4. Elastes (the Elastes). The elastic organs on the ventral segments of Machilis polypoda which assist this insect in leaping.
iii. Petiolus (the Footstalk). A slender part by which the abdomen of many Hymenoptera is united to the trunk, in some genera very long, in others very short, and in others wanting[1121]. It includes the Funiculus, Foramen, Squama, and Nodus.
1. Funiculus (the Funiculus). A small cartilaginous cord, passing through a minute orifice of the Postfrænum, just above the point where the footstalk is fixed, to an opposite hole above it, which enables the animal the better to elevate or drop the abdomen[1122].
2. Foramen (the Foramen). The orifice in the abdomen, through which the above cord passes[1123].
3. Squama (the Scale). A vertical flat scale, observable on the footstalk of the genus Formica, &c.[1124]
4. Nodi (the Knots). One or more subrotund protuberances of the footstalk in the genus Myrmica[1125].
iv. Cauda (the Tail). Where the abdomen grows suddenly slenderer, and terminates in a long jointed tail, as in Scorpio and Panorpa[1126]. It includes the Centris.
1. Centris (the Centris). The last inflated joint of the tail, terminating in the Sting.
v. Anus (the Anus). The termination of the abdomen, consisting of the two last segments. It includes the Podex, Hypopygium, Culus, Ovipositor, and Appendices.
1. Podex (the Podex). The last dorsal segment of the abdomen[1127].
2. Hypopygium (the Hypopygium). The last ventral segment of the abdomen[1128].
3. Culus (the Culus). The orifice at the end of the anus.
4. Ovipositor (the Ovipositor). The instrument of oviposition, by which the insect conducts the eggs to their appropriate nidus, and often bores a way to it; the same instrument is by some genera used as a weapon of offence, when it is called the Aculeus[1129]. It includes the Unci, Tubulus, Valvæ, Vaginula, and Terebellæ.
A Unci (the Unci). Two pair of robust organs, the upper incurved and the lower recurved, with which the anus of Locusta Leach is furnished[1130].
B Tubulus (the Tubulus). A tubular ovipositor, consisting of several pieces often retractile within each other, like the tubes of a telescope[1131].
C Valvæ (the Valves). Two lateral laminæ, often coriaceous, by which the ovipositor when unemployed is covered[1132].
D Vaginula (the Sheath). A corneous case, with two grooves, in which the Terebella or Spicula play[1133].
E Terebellæ (the Terebellæ). Instruments by which the insect saws or bores a passage for its eggs to the place in which her instinct directs her to deposit them[1134].
5. Aculeus (the Sting). The above instrument, when fitted for an offensive weapon[1135]. It includes, besides the Valvæ and Vaginula before defined, the Spicula.
A Spicula (the Darts). The proper stings which inflict the wound: retractile within the sheath, externally serrulate at the apex[1136]. They include the Retinaculum.
a Retinaculum (the Retinaculum). A minute horny moveable scale or plate with which the darts are furnished, which prevents their dislocation by being shot forth too far[1137].
vi. Appendices (the Appendages). Other instruments and organs, with which the anus of various insects is furnished. They include—the Forceps, Forfex, Furca, Styli, Foliola, Flosculus, Caudulæ, Fila, Mammulæ, Papillæ, and Siphonuli.
1. Forceps (the Forceps). A pair of anal organs that open and shut transversely, and meet at their inner margin, or at the apex. Ex. Forficula.
2. Forfex (the Forfex). A pair of anal organs, which open or shut transversely, and cross each other[1138]. Ex. Male of Raphidia Ophiopsis.
3. Furca (the Fork). An inflected elastic anal organ, ending in a fork, by which the animal is enabled to leap[1139]. Ex. Podura.
4. Styli (the Styles). Rigid, exarticulate, long and narrow anal organs[1140]. Ex. Staphylinus.
5. Foliola (the Leaflets). Rigid, exarticulate, dilated, leaf-like anal organs[1141]. Ex. Libellulina.
6. Flosculus (the Floret). A small, tubular, lunulate anal organ, with a central style[1142]. Fulgora candelaria, &c.
7. Cerci (the Cerci). Two short, flattish, sublanceolate, jointed, lateral anal organs[1143]. Ex. Blatta.—N.B. Analogous organs are observable in the Gryllina, but usually conical and without joints[1144]. In Gryllus Latr. they are setiform[1145].
8. Caudulæ (the Caudulæ). Two or more slender, filiform or setaceous, jointed, flexile anal organs[1146]. Ex. Lepisma, Machilis, Ephemera.
9. Fila (the Threads). Two exarticulate, slender, filiform anal organs[1147]. Ex. Machilis.
10. Mammulæ (the Mammulæ). Anal protuberances, containing instruments for spinning web[1148]. Ex. Araneidæ. They include the Fusi.
11. Fusi (the Spinners). Organs, consisting of two retractile pieces, issuing from the Mammulæ, and rendering the threads[1149].
12. Siphonuli (the Siphonets). Truncated, fistular, setiform anal organs, emitting a saccharine fluid[1150]. Ex. Aphis.
You will observe, that when the whole upper-side of the Truncus is spoken of, it is called the Thorax; and as in Coleoptera, and some other Orders, the whole of the Mesothorax except the Scutellum is covered by the Thorax, and the whole of the Metathorax by the Mesothorax and Elytra—the Thoracic shield, may without danger of mistake be denominated the Thorax, as it has always been. When the whole under-side of the Trunk is spoken of, it is called the Pectus. When the three Sternums are spoken of together, they may be called the Sternum; and the whole interior elevation of the Pectus may be called the Endosternum.
Before I confine my observations to the head of insects, which I propose to consider separately in the present letter, I must premise a few words upon their body in general, or rather its crust, or external integument. In this we may notice its substance, general form, sculpture, pubescence, and composition.
i. I have already noticed the substance of this integument in the preparatory states of insects[1151]; I shall not, therefore, here repeat what I then said, but restrict myself chiefly to the consideration of it as it is found in their last state, in which it is usually firmer than in their previous stages of existence. In this respect, however, it varies much in the different Orders, and even in the different genera of the same Order. In some Coleopterous insects, for instance, it is very hard, and difficult to perforate; while in others it is soft, flexible, and a pin easily passes through it[1152]. And in general, from a substance in hardness resembling horn or shell, it passes through the intermediate degrees of that of leather and parchment, almost to a thin membrane. Yet in all cases there is enough of rigidity and hardness to answer the principal uses of a skeleton—to afford, namely, a sufficient point of attachment for the muscles, and to support and defend the interior organization; so that the play and action of the vital and secretory systems may not be interrupted or impeded.
With respect to the principles which enter into the composition of this integument, very little seems to be known at present; but few insects having been submitted to a chemical analysis. The blister-beetle (Cantharis vesicatoria), from its importance in medicine, has, however, been more than once analysed; and though the products have not been very precisely stated, yet we find amongst them phosphate of lime, albumen, and some other usual components of the substance of vertebrate animals[1153]. But which of these products belong to the integument, and which to its contents, cannot be ascertained, without a separate process for each; which would not, I conceive, be very feasible. The substance, however, of the integument of insects, though we know not its precise contents, which probably vary in different genera, &c., appears not to be exactly of the nature of any of those substances after which it has usually been denominated: it is not properly analogous either to real horn, shell, skin, or leather, &c. This seems to result from the following circumstance:—Most of the excretions of vertebrate animals, as horn, skin (at least when tanned), feathers, wool, hair, &c. when exposed to the action of fire liquify, more or less, before they incinerate; emitting at the same time a peculiar and disagreeable scent: but upon applying this test to the parts of insects of the different Orders, I found, in every instance, that incineration took place without liquefaction, and was unaccompanied by that peculiar scent which distinguishes the others. Even the claws, which to the eye appear, as to their substance, exactly like those of Mammalia, birds, &c. burn without melting, and retain their form after red heat. That the insect integument is not calcareous like that of the Crustacea, and the shells of Molluscæ, you may easily satisfy yourself, by immersing them in an acid test. I made this experiment upon portions of insects of several of the Orders, in an equal mixture of muriatic acid and water, and the result was, not only that all hexapods, but octopods, Arachnida, and even Scolopendridæ, upon immersion only emitted a few air-bubbles; while, when the other myriapods, Polydesmus, Iulus, Glomeris, &c. and the Oniscidæ, were immersed, a violent effervescence took place; proving the different nature of their substance. It is remarkable that the two great branches of the Myriapods, the Scolopendridæ and Iulidæ (Chilopoda and Chilognatha Latr.), should in this respect be so differently circumstanced—the latter having a calcareous integument, and the former not.—A further difference distinguishes these two tribes: old specimens of the Iulidæ usually lose their colour and turn white, like Oniscidæ; while those of the Scolopendridæ retain it.
ii. The form of insects is so variable, that it can be reduced to no other general rules—than that, for the most part, the length exceeds the breadth, and the breadth the depth, and that the upper surface is usually convex. But to these rules there are numerous exceptions. Thus many Tetyræ F. (Scutellera Latr.), a kind of bug, are as broad as they are long[1154]; in the genus Gonyleptes K.[1155] amongst the Aptera, and Epeira cancriformis, a crab-shaped spider, the breadth exceeds the length; in Cynips, and several other Hymenoptera, in Acrida K.[1156] (Locusta F.), and other Orthopterous insects, the depth exceeds the breadth; and in that singular beetle, Eurychora; the cockroach (Blatta), &c. the upper surface is flat.
iii. The sculpture of the integument of insects is often very remarkable; but as this will call for attention hereafter, I shall only here observe in general, that ornament and variety seem not to be the sole object of those elevations and depressions which form so prominent a feature of many of the animals in question; for by means of these, many important purposes, that at first sight do not strike the observer, may be served: such as giving firmness to the crust in those places where it is most wanted; diminishing its powers of resistance in others, so that it may yield somewhat to the action of the muscles; increasing or deducting from the weight of the body, so as to produce a proper equipoise during its motions, whether on the earth, in the air, or in the water. The depressions of the outer surface of the crust, in many instances, produce an elevation of it in the interior, and so afford a useful point of attachment to certain muscles. This observation seems more especially applicable to those excavations that are common to particular tribes or genera: thus the dorsal longitudinal channel to be met with on the prothorax of most of the Carabi of Linné on the inside of the crust have a corresponding ridge. In Locusta Dux, also, (a Brazil locust,) the same part has four transverse channels, corresponding with which on the inside are as many septa, or ridges, to which muscles are attached; and those larger impressed puncta denominated puncta ordinaria, which distinguish the same part in Geotrupes and many of the Scarabæidæ, within are elevated, so as to form a kind of ginglymous articulation with the base of the anterior coxæ. The other impressed puncta so often to be seen on the different parts of various insects, which sometimes so intirely cover the surface that scarcely any interval is discoverable between them, though in many cases they appear to be mere impressions that attenuate but do not perforate the crust—yet in others, perhaps equally or more numerous, they are real pores, which pass through the integument. If, for instance, you take the thoracic shield of the cockchafer (Melolontha vulgaris), and after removing the muscle &c., hold it against the light, with the inner side towards the eye, you will see the light through every puncture: or take the elytra of Geotrupes stercorarius, or any common beetle in which these organs have punctate striæ, and examine them under a lens on the inside, and you will see distinctly that the punctures pass through the elytrum, and the membrane that lines it[1157]. It is not improbable that in the case last mentioned these pores may be of use, as the spiracles are usually closely covered by the elytra, for the better transmission of the air to those respiratory organs. Whether the pores in the other parts of the body are for transpiration, is more than I shall venture to affirm; but as insects sometimes perspire, at least this has been ascertained with respect to the hive-bee[1158], this must be by the means of some pores.
iv. The integument of insects is often clothed, either partially or generally, with pubescence, or hairs of various kinds—a circumstance which seems to have more than one object. In Parnus, Heterocerus, Gerris, Argyroneta aquatica, and some other aquatic insects, the end in view seems to be to keep the water from wetting the crust; and in this case the covering of hairs is dense, silky, and decumbent. Another object is preventing friction from being injurious: thus humble-bees, that from their mode of nidification[1159], are usually more particularly exposed to it, are well clothed with hair; and in those articulations of insects where much friction takes place, we may often observe a dense fringe or coating of the same substance. This you may see in the common stag-beetle (Lucanus Cervus), where the thorax receives the head; and very remarkably at the same point in the Hercules-beetle (Dynastes Hercules MacLeay): but besides these uses, there is probably one more universal, which will apply as well to those thinly scattered bristles and hairs, here and there one, to be noticed in many insects: but concerning this I can only throw out a conjecture, as I do not recollect ever to have seen any experiments with regard to this use of animal hairs. But may they not act as conductors, either to introduce some invisible fluid into the body in a positive state, or to convey it out, when received by other means, in a negative state? Every one knows that the fur of a cat has electric properties, and there may be an important general use of this kind attached to the fur and hairs of animals[1160]. But, as I said, I give this as a mere conjecture; and only wish it may excite your attention to the subject, and put in exercise your natural tact for experiment.