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Me Oy | Ae yous Ha tby ‘het a gars Whe Uy iba 0 de hd ld edd Maratea aes cst & dvds May nye te appt ik Wty ha. my Hcy Het, 4 ibaa ba Fiennes ty aa hh a py Dey da easing ats ; f iakeas Hee aa oP dis gu Ae yet ae prey Ser vine rey mew hl abe, i oe a witha ae ‘1 eee eae 1m? 4 , OO4 tw Bite * Pry aa oe debe bed Orr ’ ode Wp aerw thee ioupn th Ais Pe oe RE IE pad Hl ME @ abe ge adh > WR ty Hitt yf adh —iee pe aA? th cay as aback rae nk aay p- Ce eee ob Hen 1 eek# made Wie erme ess A ee MSC OLA i i a ar aie wt m Ache ss beth anion ow (8 Po » he heave: bse bad teat th, one Oe Laan eater “og tn SaeTta ss ! an ae : : : ca ; ee a Pl eat ; ; ve ‘ ers) ee) ee prereerict ahs +e MEAVEGGT GE In IN Mire Peeters f nee tis we Nstat Gee ey ere V4 ee ee eo Wp Vs btn 4 We ‘ ” hee had tena nash LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN THE INSECT WORLD: A POPULAR ACCOUNT OF THE ORDERS OF INSECTS, TOGETHER WITH A DESCRIPTION OF j THE HABITS AND ECONOMY OF SOME OF THE MOST INTERESTING SPECIES. hes oo eee OS IB, asthe, FROM THE FRENCH OF LOUIS FIGUIER\<. AUTHOR OF “THE WORLD BEFORE THE DELUGE,” “ THE VEGETABLE” WORLD,” ‘(THE OCEAN WORLD,” ETC., ETC. “Sa ILLUSTRATED BY 564 WOODCUTS. BY MM. E. BLANCHARD, DELAHAYE, AFTER REAUMUR, ETC LONDON : CHAPMAN AND HALL, 193, PICCADILLY. 1868. KDITOR’S PREFACE. E following translation of M. Figuier’s ‘Les Insectes” was ; into my hands, chiefly for the purpose of rendering the anicalities and the names of species, when made necessary the use of French vernaculars, intelligible to Iinglish readers. this not always easy task, I have received much kind stance from Mr. Janson and Mr. F. P. Pascoe, to whom I r my best thanks. Beyond this, some generic synonyms of juent use, placed between brackets, some foot-notes en passant, ew remarks on the occurrence of individual species in this ntry, and the insertion of the short chapter on the Order spsiptera, I have interfered but little with the sense of the rinal. Mee)! LEYGATE, NEAR NsHER, SURREY, April, 1868. SS iS) 3 The Dragon-fly (Libellula depressa). A. Perfect insect. 3B. Perfect insect emerging from the pupa. c.D. Larvx and pupz. Frontispiece. CONTENTS. ) a PAGE INTRODUCTION 1 APTERA 29 DIPTERA 36 Nemocera : phen 3t Brachycera . ; . . 62 HEMIPTERA 90 Heteroptera al Homoptera , 102 LEPIDOPTERA 141 | The Larva, or Caterpillar 14] The Chrysalis, or Pupa 149 | The Perfect Insect 169 | ORTHOPTERA 283 : HYMENOPTERA 312 NEUROPTERA 404 STREPSIPTERA 434 COLEOPTERA 436 INDEX ant Seine THE INSECT WORLD. INTRODUCTION. ‘ is not intended here to thoroughly investigate the anatomy ‘Insects ; but, as we are about to speak of the habits and economy certain created beings, it is necessary first to explain the meipal parts of their structure, and the stage fect insect or zmago has under ite. 8 which every gone before arriving at that We therefore proceed to explain, as simply as may be, the atomy of an insect, and the functions of its organs. If we take an insect, and turn it over e first thing that strikes us is that it is divided into three parts : e head; the thorax, or chest; and the abdomen, or stomach. The head (Fig. 1) is a kind of box, formed of a single piece, ving here and there joints more or less strongly marked, some- Ges scarcely visible. It is furnished in front th an opening—often very small—which the mouth; and with others for the eyes, d for the insertion of the antenne, or horns. The integuments of the head are generally rder than the other parts of the body. It necessary that this should be so. Insects cen live and die in the midst of substances uich offer some resistance. erefore, tl] , and examine it carefully, Fig. 1.—Head of an It is necessary, wii hat the head be strong enough to over ice. The head contains the masticatory organs, which, frequently come such resist- B 2 THE INSECT WORLD. having to encounter hard substances, must be strongly supported. The exception to this rule is among insects which live by suction. It would be out of place here to mention the numerous modifi- cations of the head which are presented in the immense series of the class of insects. The eyes of insects are of two kinds, called compound eyes, or eyes composed of many lenses, united by their margins and forming hexagonal facettes; and simple eyes, or ocelli, called also stemmata. The exterior of the eye is called the cornea (Fig. 2), each facette being a Fig. 2.—A Compound ae cornea; but the facettes unite and form a common cornea, which is represented by the entire figure: these facettes vary 10 size even in the same eye. In order to show the immense number of these facettes possessed by many insects, we give the following list :— In the genus Mordella (a genus of beetles) the eye has 25,008 facettes. In the Lebellula (dragon-fly) - + + + ° 12,544 = ,, In the genus Papilio (a genus of butterflies) . - - 17,355 5, In Sphinx convol pult (the convolvulus hawkmoth) . .- 1,300 —,, In Bombyx mori (the common silkworm moth). - -: 6,236. 55 Tahoe bonsgesfiy 2 Fuss) & Fon wee 4,000 __—,, Tn the ant Me t+ otis, oo ee ate eee BO Ri ss Tithe cockehater) oi. 2 a eye eee 8,820 4, The facettes appear to be most numerous in insects of the genus Scarabeus (a genus of beetles). They are so minute, that they can scarcely be detected with a glass. Looked at in front, a compound eye might be considered an agelomeration of simple eyes ; but internally its structure is altogether different. On the under side of each facette we find a body of a gellatinous appearance, transparent, and usually conical ; the base of which occupies the centre of the facette in such a manner as to leave around it a ring to receive the pigment. This body diminishes sn thickness towards its other extremity, and terminates in a point where it joins a nervous filament, proceeding from the optic nerve. These cones, agreeing in number with the facettes, play INTRODUCTION. the part of the crystalline, or lens, in the eyes of animais, They are straight and parallel with each other. A pigment fills all the Spaces between the cones, and between the nervous filaments, and covers the underside of each cornea, except at the centre. This pigment varies much in colour. There are almost always two layers, of which the exterior one is the more brilliant. In fact, these eyes often sparkle with fire, like precious stones. M. Lacordaire, in his “Introduction a ’Entomologie,” from which we borrow the greater part of this information, has summed up as follows, the manner in which, according to Miiller, the visual organs of insects operate :— “Each facette with its lens and nervous filament, separated from those surrounding them by the pigment in which they are enclosed, form an isolated apparatus, impenetrable to all rays of light, except those which fall perpendicularly on the centre of the facette, which alone is devoid of pigment. All rays falling obliquely are absorbed by that which surrounds the gelatinous cone. It results partly from this and partly from the immobility of the eye that the field of vision of each facette is very limited, and that there are as many objects reflected.on the optic filaments as there are corner. The extent, then, of the field of vision will be determined, not by the diameter of these last, but by the diameter of the entire eye, and will be in proportion to its size and con- vexity. But whatever may be the size of the eyes, like their fields of vision, they are independent of each other; there is always a Space, greater or less, between them; and the insect cannot see objects in front of this space without turning its head. What a peculiar sensation must result from the multiplicity of images on the optic filaments! This is not more easily explained than that which happens with animals which, having two eyes, see only one image; and probably the same is the case with insects. But these eyes usually look in opposite directions, and should see two images, as in the chameleon, whose eyes move independently of each other. The clearness and length of vision will depend, continues M. Miller, on the diameter of the sphere of which the entire eye forms a.segment, on the number and size of the facettes, and the length of the cones or lenses. The larger each facette, taken separately, and the more brilliant the pigment placed Be ~~ 4 THE INSECT WORLD. between the lenses, the more distinct will be the image of objects at a distance, and the less distinct that of objects near. With the latter the luminous rays diverge considerably ; while those from the former are more parallel. In the first case, in traversing the pigment, they impinge obliquely on the crystalline, and consequently confuse the vision ; in the second, they fall more perpendicularly on each facette. “Objects do not appear of the same size to each optic filament, unless the eye is a perfect section of a sphere, and its convexity concentric with that of the optic nerve. Whenever it is other- wise, the image corresponds more or less imperfectly with the size of the object, and is more or less incorrect. Hence it follows, that elliptical or conical eyes, which one generally finds among insects, are less perfect than those referred to above. “The differences which exist in the organisation of the eye among insects, are explicable to a certain point, on the theory which we are about to explain in a few words. Those species which live in the same substances on which they feed, and those which are parasitical, have small and flattened eyes ; those, on the contrary, which have to seck their food, and which need to see objects at a distance, have large or very convex eyes. For the same reason the males, which have to seek their females, have larger eyes than the latter. The position of the eyes depends also on their size and shape; those which are flat, and have consequently a short field of vision, are placed close together, and rather in front, than at the sides of the head, and often adjoin- ing. Spherical and convex eyes, on the contrary, are placed on the sides, and their axes are opposite. But the greater field of vision which they are able to take in makes up for this position.” Almost all insects are provided with a pair of compound eyes, which are placed on the sides of the head. The size and form of these organs are very variable, as we shall presently see. They are generally placed behind the antenne. We do not find simple eyes (ocelli or stemmata) in all the orders of insects, although we frequently find them. They are generally round, and more or less convex, black, and to the number of three in the majority of cases. In this case they are most frequently placed in a triangle behind, and at a greater or less POLES INTRODUCTION. distance from the antenne. Under the cornea, which varies in convexity, is found a transparent, rather hard, and nearly globular body, which is the true crystalline resting on a sort of lens, which represents the vitreous body. This vitreous body is enclosed in an expansion of the optic nerve. Besides these, there is a pigment, most frequently red-brown, sometimes black, or blood-red. The organisation of these eyes is analogous to the eyes of fishes, and their refractive power is very great. With these insects can only see such objects as are at a short distance. Of what use then can stemmata be to insects also pro- vided with compound eyes? It has been remarked that insects having this arrangement of eyes feed on the pollen of flowers, and it has been surmised that these stemmata enable them to distin- guish the parts of the flowers. The antenne, commonly called horns, are two flexible appen- dages of very variable form which are Joined to different parts of the head, and are always two in number. The joints of which they are made up have each the power of motion, and enable the insect to move them in any direction. The antennz consist of three parts,—the basal joint, commonly distinguished by its form, length, and colour; the club formed by a gradual or sudden thickening of the terminal joints, of which the number, form, and size present great variations ; lastly, the stalk formed by all the joints of the antenne, except the basal one when no club exists, and in case of the existence of a club, of all those be- tween it and the basal one. Yi We give as examples the anten- ty ne of two beetles, one of the genus y Asida, the other of the genus Zygia iy (Figs. 3 and 4). ne Insects for the most part, while ‘. in repose, place their antenne on \¥ their backs, or along the sides of the Fig. 3.—Antenna of a Fig 4.—Antenna of head, or even on the thorax. Others *?°i@8 of Asida. ah eR as are provided with cavities in which the antenne repose either wholly or in part. — ———EE 6 THE INSECT WORLD. During their different movements, insects move their antenns more or less, sometimes slowly and with regularity, at other times ++ all directions. Some insects impart to their antenne a perpetual vibration. During flight they are directed in front, perpendicular to the axis of the body, or repose on the back. What is the use of the antenne, resembling, as they do, feathers, saws, clubs, &c.? Everything indicates that these organs play a very important part sn the life of insects, but their functions are imperfectly understood. Experience has shown that they only play a subordinate part as feelers, and have nothing to do with the senses of taste or smell. There is no other function for them to fulfil except that of hearing. On this hypothesis the antennz will be the principal instru- ments for the transmission of sound waves. The membrane at their base represents a trace of the tympanum which exists among the higher animals. This membrane then will be an auditory nerve. Situated intermediately between the inferior animals, whose functions more or less resemble those of plants, and the vertebrates, whose functions are localised in a very high degree, insects have received, like these latter, special organs for nutrition. The mouth is the most exterior of these apparatuses. The mouth of insects is formed after two general types, which correspond to two kinds of requirements. It is suited in the one case to break solid substances, in the other to imbibe liquids. At first sight there seems no sim1- larity between the mouth of a grind- ing insect and of one living by suction. But on examination it 18 found that the parts of the mouth in the one animal are exactly ana- " logous to the same parts in the other, Fig.5.—Mouth of a masticating and that they have only undergone me modifications suiting them to the different purposes which they have to fulfil. The mouth of a breaking insect is composed of an upper lip, a pair of mandibles, a pair of jaws, and a lower lip (Fig. 5). INTRODUCTION. 7 The lower lip and the jaws carry on the outside certain nervous filaments which have received the name of palpi. When speaking of sucking insects, and in general of the various orders of insects, we shall speak more in detail of the various parts of the mouth. The thorax (Fig. 6), the second primary division of the body of insects, plays almost as important a part as the head. It con- sists of three segments or rings, the prothorax, the mesothorax, and the metathorax, each of which bears a pair of legs, and they are in general joined to- 3 gether. The wings are attached Fig! atoms of Acrotinus lonpiidanna to the two posterior segments. Sa iar All insects have six legs. There is no exception whatever to this rule, though some may not be developed. After the segments to which they are attached the legs are called anterior, posterior, and intermediate. The legs are com- posed of four parts: the trochanter, a short joint which unites the thigh to the body, the thigh or femur, the tibia, answering to the shank in animals, and the tarsus, or foot, composed of a variable number of pieces placed end to end and called the phalanges. We take for example the front leg of a AHeterocerus (Fig. 7), and the posterior leg of a Zophosis (Fig. 8), genera of beetles. We shall not dwell on the different parts, as they perform functions which will occupy us later, when speaking of the various species of the great class of insects. Fig. 7.—Hind leg of a Fig. 8.—Front leg The functions which the e!rocerus. Se legs of insects have to perform consist in walking, swimming, or jumping. In walking, says M. Lacordaire, insects move their legs 8 THE INSECT WORLD. in different ways. Some move their six legs successively, or only two or three at a time without distinction, but never both legs of the same pair together, consequently one step is not the same as another. The walk of insects is sometimes very irregular, espe- cially when the legs are long; and they often hop rather than walk. Others have one kind of step and walk very regularly. They commence by moving the posterior and anterior legs on the same side and the intermediate ones on the opposite side. The first step made, these legs are put down, and the others raised in their turn to make a second. Running does not change the order of the movements, it only makes them quicker—very rapid in some species, and surpassing in proportion that of all other animals; but in others the pace is slow. Some insects rather crawl than walk. In swimming, the posterior legs play the principal part. The other legs striking the water upwards or downwards, produce an upward or downward motion. The animal changes its course at will by using the legs on one side only in the same way as one turns a rowing boat with one oar without the aid of the rudder. Swimming differs essentially from walking, for the foot being surrounded by a resisting medium, the legs on both sides are moved at the same time. The act of jumping is principally performed by the hind legs. Insects which jump have these legs very largely developed, as in the figure (Fig. 9). When about to jump they bring the tibia into contact with the thigh, which is often furnished with a groove to receive it, having on each side a row of spines. The leg then suddenly straightens like a spring, and the foot being placed firmly on the ground, sends the insect into the air and at the same time propels forward. The jump is greater in proportion as the leg is longer. To speak here in a general manner of the wings of insects would be too vague. We shall speak of them at length in their Fig. 9.—Posterior leg of a jumping insect. INTRODUCTION. 9 proper place, when speaking of the various types of winged insects. In the perfect insect (of which we have been speaking in the preceding pages) the abdomen does not carry either the wings or the legs. Itis formed of nine segments, which are without appendages, with the exception of the posterior ones, which often carry small organs differing much in form and function. These are saws, probes, forceps, stings, augers, &e. We will speak later of these different organs in their proper places. With vertebrate animals, which have an interior skeleton suited to furnish points of resistance for their various movements, the skin is a more or less soft covering, uniformly diffused over the exterior of the body, and intended only to protect them against external injury. In insects the points of resistance are changed from the interior to the exterior. The skin changes in nature to fit it to this purpose. It becomes hard, and presents between the segments only membraneous intervals, which allow the hard parts to move in all directions. We are examining a perfect insect ; we have glanced at its skeleton and the different appendages which spring from it. The principal organs which are contained in the body remain to be examined. We will first study the digestive apparatus. This apparatus consists of a lengthened tubular organ, swollen at certain points, forming more or less numerous circumyolutions, and provided with two distinct orifices. This alimentary canal is always situated in the median line of the body, the nervous ganglia.* In its most complicated form the alimentary canal is composed of an wsophagus, or gullet, of a crop, of a gizzard, of a chylific ventricle, a small intestine, a large intestine, divers appendages, salivary, biliary, and urinary glands. The cesophagus is a duct often not thicker than a hair, in many species enlarged into a pouch, which is called the crop because it occupies the same position, and performs analogous functions with that organ in birds. It is enough to say that the food remains there some time before passing on to the other parts of the intestinal canal, and undergoes a certain amount of preparation. It is in the gizzard, * Ganglion, a collection of nerves.—Ep. 10 THE INSECT WORLD. when one exists, that the food, separated by the masticatory organs of the mouth, undergoes another and more complete grinding. Its structure is suited to its office. It is, in fact, very muscular, often half cartilaginous, and strongly contractile. Its interior walls are provided with a grinding apparatus, which varies according to the species, and consists of teeth, plates, spines, and notches, which convert the food into pulp. It only exists among insects which live on solid matters, hard vegetables, small animals, tough skin, &c. This apparatus is absent in sucking insects and those which live on soft substances, such as the pollen of flowers, &c. The chylific ventricle is never absent; it is the organ which performs the principal part in the act of digestion. Two kinds of appendages be- long to the chylific ventricle, but only in certain families. The first are papille, in the form of the fingers of a glove, which bristle over the exterior of this organ, and in which it is believed that the food begins to be con- verted into chyle. The second are ceca, and larger and less numerous. They have been considered ‘as secretory organs, answering to the pancreas in vertebrate ani- | mals. Fig. 10.—Digestive apparatus of Carabus auratus. Fi g. 10, whi ch repres ents th e digestive apparatus of Carabus auratus, a common beetle, presents to the eyes of the reader the different organs of which we are speaking. A is the mouth of the insect, B the cesophagus, c the crop, D the gizzard, E the chylific ventricle, r and G the small and large intestines, and H the anus. We will not mention the other parts of the alimentary canal in INTRODUCTION. 11 insects. We will only speak of some of the appendages of this apparatus. The salivary glands pour into the digestive tube a liquid, gene- rally colourless, which, from the place where it is secreted, and its alkaline nature, corresponds to the saliva in vertebrate animals. It is this hquid which comes in the form of drops from the tongue of sucking insects. These vessels are always two in number. Their form is as variable as complicated. The most simple is that of a closed flexible tube, generally rolled into a ball, and opening on the sides of the cso- phagus. At the posterior extremity of the chylific ventricle are inserted a vari- able number of capillary tubes, usually elongated and flexible, and terminating in culs-de-sac. Their colour, which de- pends on the liquid which they contain, is sometimes white, but more frequently brown, blackish, or green. They appear to be composed of a very slight and deli- cate membrane, as they are very easily torn, and nothing is more difficult than to unroll and ‘to disengage them from the fatty or other tissues by which they are enveloped. The function of these vessels is un- certain. Cuvier and Léon Dufour sup- posed them to be analogous to the liver, and on that account they have been called biliary vessels ; but as this opinion is not generally held, it has been agreed to call them the Malpighian vessels, after the name of their discoverer. According to M. Lacordaire, their func- tions vary with their position. When ~ Fig. 11.—Posterior extremity of the chylific ventricle, surrounded by the Malpighian vessels. they enter the chylific ventricle, they furnish only bile; bile and a urinary liquid when they enter the posterior part of the ventricle 12 THE INSECT WORLD. aad and the intestine, and urine alone when they are placed near the posterior extremity of the alimentary canal. Fig. 11 represents part of the preceding figure more highly magnified, showing the manner in which these tubes enter the chylific ventricle. In our rapid description of the digestive apparatus of insects, it only remains for us to mention certain purifying organs which secrete those fluids, generally blackish, caustic, or of peculiar smell, which some insects emit when they are irritated, and which cause a smarting when they get into one’s eyes. Less widely diffused than the salivary organs, they are often of a very complicated structure. In Fig. 12 is represented the secre- tory apparatus of the Carabus auratus, which will serve for an example : a represents the secre- tory sacs aggregated together like a bunch of grapes, B the canal, c the pouch which receives the secre- tion, p the excretory duct. Tiito Cites tctene aeparaci or Oarabrs Sometimes the secretion is OR iy a liquid, and has a foetid or ammo- niacal odour; sometimes, as in the Bombadier beetle (Brachinus crepitans), it is gaseous, and is emitted with an explosion in the form of a whitish vapour, having a strong pungent odour ana- logous to that of azotic or nitric acid, and the same properties. It reddens litmus paper, and burns and reddens the skin, which after a time becomes brown, and continues so for a considerable time. About the middle of the seventeenth century Malpighi at Bologna, and Swamerdam at Utrecht, each discovered in different insects a pulsatory organ occupying the median line of the back, which appeared to them to be a heart. Nevertheless, Cuvier, haying declared some time afterwards that there was no circula- INTRODUCTION. 13 tion, properly so-called, among insects, his opinion was universally adopted. But in 1827 a German naturalist named Carus discovered that there were real currents of blood circulating throughout the body, and returning to their point of departure. The observations of Carus were repeated and confirmed by many other naturalists, and we are thus enabled to form a sufficiently exact idea of the manner in which the blood circulates. The following summary of the phenomena of circulation among insects is borrowed from ‘ Lecons sur la Physiologie et l’Ana- tomie comparée”’ by M. Milne Edwards :— The tube which passes under the skin of the back of the head, and front part of the body, above the alimentary canal, has been known for a long time as the dorsal vessel. It is composed of two very distinct portions : the anterior, which is tubular and not contractile, and the posterior, which is larger, of more complicated structure, and which contracts and dilates at regular intervals. This latter part constitutes, then, more particularly the heart of the insect. Generally it occupies the whole length of the abdomen, and is fixed to the vault of the tegumentary skeleton by membra- neous expansions in such a manner as to leave a free space around it, but shut above and below so as to form a reservoir into which the blood pours before penetrating to the heart. This reservoir is often called the auricle, for it seems to act as an instrument of impulsion, and to drive the blood into the ventricle or heart, properly so called. a The heart is fusiform, and is divided by numerous strictures into chambers. ‘These chambers have exits placed in pairs, and mem- braneous folds which divide the cavity in the manner of a portcullis. The lips of the orifices, instead of terminating in a clean edge, penetrate into the interior of the heart in the form of the mouth- piece of a flute. The double membraneous folds thus formed on each side of the dorsal vessel are in the shape of a half moon, and separate from each other when this organ dilates; but the contrary movement taking place, the passage 1s closed. By the aid of this valvular apparatus, the blood can penetrate the heart from the pericardic chamber, the empty space surrounding the heart, but cannot flow back from the heart into that reservoir. 14 THE INSECT WORLD. The anterior or aortic portion of the dorsal vessel shows neither fan-shaped lateral expansions, nor orifices, and consists of a single membraneous tube. On reaching the interior of the head it opens in the lacunary inter-organic system. The whole of the blood set in motion by the contractions of the cardial portion of the dorsal vessel runs into the cavity of the head, and circulates after- wards in irregular channels formed by the empty spaces left between the different organs. It is the unoccupied portions of the great visceral cavity which serve as conductors to the blood, and through them run the main currents that one sees in the lateral and lower parts of the body, whence these currents regain the back part of the abdomen, and enter the heart after having traversed externally the different organs they encountered. These principal channels are in continuity with other gaps provided between the muscles, or between the bundles of fibres of which these muscles are composed, or else in the interior of the intes- tines. The principal currents send into the network thus formed minor branches, which, having ramified in their turn among the princi- pal parts of the organism, re-enter some main current to regain the dorsal vessel. In the transparent parts of the body the blood may be seen circulating in this way in a number of inter-organic channels, more or less obvious, penetrating the limbs, overspreading the wings, when these appendages are not horny, and, in short, diffusing itself everywhere. “If, by means of coloured injec- tions,” says M. Milne Edwards, ‘one studies the connections which exist between the cavities in which sanguineous currents have been found to exist, and the rest of the economy, it is easy to see that the irrigatory system thus formed penetrates to the full depth of every organ, and should cause the rapid renewal of the nourishing fluid in all the parts where the process of vitality renders the passage of this fluid necessary.” We shall see presently, in speaking of respiration, that the relations between the nourishing fluid and the atmospheric air are more direct and regular than was for a long time supposed. In short, insects possess an active circulation, although we find neither arteries nor veins; and although the blood put in motion INTRODUCTION. 15 by the contractions of the heart, and carried to the head by the aortic portion of the dorsal vessel, can only distribute itself in the different parts of the system to return to the heart, by the gaps left between the different organs, or the membranes and fibres of which these organs are composed. Fig. 13 (page 17), which shows both the circulating and breathing systems of an insect, enables us to recognise the different organs which we have described, as helping to keep up both respiration and circulation. The knowledge of the respiration of the insect is a scientific acquisition which is quite modern. Malpighi was the first to prove, in 1669, that these animals are provided with organs of respiration, and that air is as indispensable to insects as it is to other living beings. But the opinion of this celebrated naturalist has been contradicted, and his views have been contested, even in the present day. Now, however, one can easily recognise the apparatus by the aid of which the respiration of the insect is effected. In all these animals the respiratory apparatus is essentially composed of membraneous ducts of great tenuity, of which the ramifications in incalculable numbers spread everywhere, and bury themselves in the different organs, much in the same way as the fibrous roots of plants bury themselves in the soil. These vessels are called trachew. Their communications with the air are externally established in different ways, according to the cha- racter of the medium in which the insect lives. It is well known that the greater part of all insects live in the air. ‘This air penetrates into the trachez by a number of orifices placed at the sides of the body, which are termed spiracles. On close examination these may be seen, and are in the shape of button-holes in a number of different species. Let us dwell for a moment on the breathing apparatus of the insect, that is to say, the trachez. This apparatus is sometimes composed of elastic tubes only, sometimes of a collection of tubes and membraneous pouches. We will first speak of the former. The coats of these-breathing tubes are very elastic, and always preserve a cylindrical form, even when not distended. This state of THE INSECT WORLD. 16 things is maintained by the existence, throughout the whole length of the trachea, of a thread of half horny consistency, rolled up in a spiral, and covered externally by a very delicate membraneous sheath. The external membrane is thin, smooth, and generally colourless, or of a pearly white. The cartilaginous spiral is some- times cylindrical, sometimes flat, and also resembles mother-of- pearl. It only adheres slightly to the external membrane, but 1s, on the other hand, closely united to the internal one. This spiral thread is only continuous in the same trunk; it breaks off when it branches, and each branch then possesses its own thread, in such a way that it is not joined to the thread of the trunk from which it issued, except by continuity, just as the branch of a tree is attached to the stem which supports it. This thread is prolonged, without interruption, to the extreme points of the finest ramifications. The number of trachez in the body of an insect is very great. That patient anatomist, Lyonnet, has proved to us, in his great work on the goat-moth caterpillar, Cossus ligniperda, that the insect has much affinity as regards its muscles with animals of a superior class. Lyonnet, who congratulated himself on having finished his long labours without having had to destroy more than eight or nine of the species he wished to describe, had the patience to count the different air-tubes in that caterpillar. He found that there were 256 longitudinal and 1,336 transverse branches; in short, that the body of this creature is traversed in all directions by 1,572 aeriferous tubes which are visible to the eye by the aid of a magnifying glass, without taking into account those which may be imperceptible. The complicated system of the breathing apparatus which we are describing is sometimes composed of an assemblage of tubes and membraneous pouches, besides the elastic tubes which we have already mentioned. These pouches vary in size, and are very elastic, expanding when the air enters, and contracting when it leaves them, as they are altogether without the species of frame- work formed by the spiral thread of the tubular trachex, of which « they are only enlargements. These, which are called vesicular trachee, more especially belong to those species whose flight is frequent and sustained, such as the grasshopper, the humble-bee, the bee, the fly, the butterfly, &c. INTRODUCTION, , 17 It will be necessary to look at Fig. 13 in order to see the oreans d ro) DoD of respiration of which we are speaking. The respiratory mechanism of an insect is easily understood. Fig. 13.—A, abdominal portion of the dorsal vessel. B, aortic or thoraic portion. ¥ head ; D, of the abdomen, “The abdominal cavity,” says Mr. Milne Edwards, “in which is placed the greater part of the respiratory apparatus, is susceptible C C, air-vessels of the 18 THE INSECT WORLD. ted and dilated alternately by the play of the s of which the skeleton is composed, and which a manner that they can be drawn into each other to a greater or less extent. When the insect contracts its essed and the air driven out. But body the tracheze are compr when, on the other hand, the visceral cavity which contains the trachese assumes its normal size or dilates, these channels become larger, and the air with which they are filled being rarefied by in equilibrium with the outer air with hrough the medium of the spiracles. he interior of the respira- of being contrac different segment are placed in such this expansion, is no longer which it is in communication t The exterior air is then impelled into t tory tubes, and the inspiration is effected.” The respiratory movements can be accelerated or diminished, according to the wants of the animal; in general, there are from thirty to fifty to the minute. In a state of repose the spiracles are open, and all the trachese are free to receive air whenever the visceral cavity is dilated, but those orifices may . be closed, and the insect thus possesses the faculty of stopping all communication between the respiratory apparatus and the sur- rounding atmosphere. Some insects live in the water; they are therefore obliged to come to the surface to take the air they are in need of, or else to possess themselves of the small amount contained in the water. Both these methods of respiration exist under different forms in aquatic insects. To inhale atmospheric air, which 1s necessary for respiration, above the water, certain insects employ their elytra* as a sort of re- servoir ; others make use of their antenne, the hairs of which retain the globules of air. In this case it is brought under the thorax, whence a groove carries it to the spiracles. Sometimes the same result is obtained by amore complicated arrangement, consisting of respiratory tubes which can be thrust into the air, which it is their function to introduce into the organisation. Insects which breathe in the water without rising to the sur- face are provided with gills; organs which, though variable in form, generally consist of foliaceous or fringed expansions, in the midst of which the trachez ramify in considerable numbers. These * The horny upper wings with which some insects are provided are called elytra. —~Eip. INTRODUCTION. 19 vessels are filled with air, but it does not disseminate itself in them directly, and it is only through the walls of these tubes that the contained gas is exchanged for the air held in suspension by the surrounding water. The oxygen contained in the water passes through certain very permeable membranes of the gill and pene- trates the trachee, which discharge, in exchange, carbonic acid, which is the gaseous product of respiration. Fig. 14 represents the gills or breathing apparatus in an aquatic insect. We take as an example the Eiphemera.* Jt may be observed that the gills or foliaceous laminz are placed at the circumference of the body, and at its smallest parts. — We have now seen that the respi- ratory apparatus is considerably de- veloped in insects; itis, therefore, easy to foresee that those functions are most. actively employed by them. In fact, if one compares the oxygen they im- bibe with the heavy organic matter of which their body is composed, the amount 1s enormous. Before finishing this rapid examina- tion of the body of an insect, we shall have to say a few words on the nervous system. This system is chiefly composed of a double series of ganglions, or collections of nerves, which are united together by longitudinal cords. The number of these ganglions corresponds with that of the segments. Sometimes they are at equal distances, and extend inachain from one end of the body to the other; rig. 14.—Branchie or gills of an aquatic at others they are many of them close We PS aaah together, so as to form a single mass. The cephalic ganglions are two'in number; they have been A, foliaceous laminee or gills. * May-fly family.—Eb., C2 20 THE INSECT WORLD. described by anatomists under the name of brain. “ This ex- pression,” says M. Lacordaire, “ would be apt to mislead the reader, as it would induce him to suppose the existence of a concen- tration of faculties to assemble the feelings and excite the move- ments, which is not the case. The same naturalist observes, ‘All the ganglions of the ventral chain are endowed with nearly the same properties, and represent each other uniformly.” The ganglion situated above the csophagus gives rise to the optic nerves, which are the most considerable of all those of the body, and to the nerves of the antenne. The ganglion beneath the csophagus provides the nerves of the mandibles, of the jaws, and of the lower lip. The three pairs of ganglions which follow those placed immediately below the cesophagus, belong to the three segments of the thorax, and give rise to the nerves of the feet and wings. They are in general more voluminous than the following pairs, which occupy the abdomen. Fig. 15 represents the nervous system of the Carabus auratus ; Ais the cephalic ganglion; B, the sub-cesophagian ganglion; c, the prothoracic ganglion; p and E are the ganglions of the meso- thorax and metathorax. The remainder, F F, are the abdominal ganglions. 99 & Before finishing these preliminary observations, it 18 necessary to say that the preceding remarks only apply absolutely to insects arrived at the perfect state. It is important to make this remark, as insects, before arriving at that state, pass through various other stages. These stages are often so different from each other, that it would be difficult to imagine that they are only modifications of the same animal; one would suppose that they were as many different kinds of animals, if there was not abundant proof of the contrary. The successive stages through which an insect passes are four in number: the egg ; the larva; the pupa, nymph or chrysalis ; and the perfect insect or imago. The egg state, which is common to them, as to all other articu- late animals, it is unnecessary to explain. Nearly all insects lay eggs, though some few are viviparous. ‘There often exists in the extremity of the abdomen of the female a peculiar organ, called * Introduction 4 l’Entomologie, tome ii. p. 192. In 8vo. Paris. 1838. INTRODUCTION. 21 tod | the ovipositor, which is destined to make holes for the reception of | the eggs. By a wonderful instinct the mother always lays her egos / ina place where her young, on being hatched, can find an abundance of nutritious substances. It will not be needless to observe that in most cases these aliments are quite different to those which the mother seeks for herself. In the second stage, that is to say, on leaving the egg—the x Os | , f ee Ve a? ' Vly s Y 4) \/ ‘ ! \