Insects.] 



MUSEUM OF ANIMATED NATURE. 



339 



Tig. 3380, the under surface of a dipterous insect, 

 showing the poisers very distinctly, and also the ner- 

 vures of the wings ; together with the terminal 

 suckers of the feet. 



Fi<r». 3381, 3382, and 3383 show the feathered and 

 scaled character of the wings of moths ; among 

 these insects the plume-moths (Alucitidae) are ex- 

 ceptions as it respects the structure of the wings ; 

 these, instead of consisting each of one single piece, 

 are composed of numerous distinct shafts, fringed 

 with most delicate barbs or cilia, Uke a downy 

 feather. The white-plume moth (Pterophorus pen- 

 tadactylus, Leach ; Alucita pentadactyla) is by no 

 means uncommon, during the summer, along hedge- 

 rows, slowly winnowing its way, like a flake of 

 snowy down. 



Fig. 3384 represents — a, the twenty-plume moth 

 (Alucita hexadactylai, of the natural size ; b, the 

 same magnified : c, the white-plume moth. 



When we consider the ease and velocity with 

 which insects fly, the extreme rapidity ofthe vibra- 

 tions of their wings, at least in many species, which 

 the eye cannot follow, and the length of time they 

 are capable of continuing on the wing, we may 

 readily conclude that the muscles destined for 

 moving these organs must possess extraordinary 

 vigour and power of endurance. M. Chabrier 

 describes two sets of muscles in the diptera, appro- 

 priated to the wings, a dorsal series placed length- 

 wise in the thorax for lowering the wings, and the 

 sterno-dorsal, passing obliquely across the former ; 

 these raise the wings. In the dragon-flies there 

 is another set of muscles, called pectoral, placed 

 lengthwise, and inserted immediately into the 

 wings. 



Figs. 3385 and 3386 show the muscles of flight in 

 a dipterous insect (Syrphus inanis) : a, part of the 

 abdomen ; b, the costo dorsal muscles; c, and d, 

 the sterno-dorsal muscles; e, part ofthe head. 



We may now pass on to a consideration of the 

 circulation and respiration of insects. 



Insects breathe through a series of pores disposed 

 in regular succession along the sides of the chest 

 and body. These orifices are termed spiracles or 

 stigmata. In many instances they may be seen 

 with the naked eye; and though in some species 

 they are always open and circular, in others they 

 are capable of being closed and opened alternately. 

 In numerous insects they are defended by a pencil 

 of hairs, in order to prevent the intrusion of dust or 

 foreign particles. These spiracles generally lead 

 to two main internal branches running longitudi- 

 nally, and termed tracheae, whence multitudes of 

 tubes are given off dividing almost ad infinitum and 

 penetrating every part. These tubes generally ap- 

 pear to be simple, but sometimes assume a bearded 

 appearance, and sometimes numbers of them are 

 dilated at certain intervals into sacculi or reservoirs, 

 partly, perhaps, for the preservation of air, and 

 partly, perhaps, as in the sacculi of birds, to lighten 

 the specific gravity ofthe body during flight. These 

 tubes, however, are not confined to the body, they 

 are continued into the wings, constituting, as already 

 .stated, the nervures ; and in such insects as fold up 

 the wings, most naturalists, we believe, consider 

 that it is by forcing the air into these tubes that the 

 expansion of the wings for flight is efi'ected. Thus, 

 then, insects may be said to be permeated by air ; 

 and to this circumstance their vigour and energy 

 are greatly owing, for every part of their organiza- 

 tion, their muscles, and the nutritive fluids, are 

 under the constant operation of oxygen. The mul- 

 titude of these air-vessels is not less surprising than 

 their structure. As far as observation lias hitherto 

 gone, the trachese at least are found to consist not 

 of a simple membranous tissue forming a cylinder, 

 but of two exquisitely fine membranes, between 

 which a spiral thread is interposed so as to form by 

 its close gyrations a cylinder like the worm spring of 

 wire used in bell-hanging. The object of this won- 

 derful contrivance is to give firmness to the tubes 

 without interfering with their flexibility, and to pre- 

 vent their collapse, without their being rigid or 

 coriaceous. The external signs of respiration are 

 not always to be perceived in insects ; in some, 

 however, as the bee, the great dragon-fly, and the 

 large green grasshopper, it is indicated by the al- 

 ternate expansion anc^ contraction of the abdomen, 

 which M. Chabrier has described in detail. In the 

 grasshopper M. Vauquelin found the inspirations to 

 be fifty-five times in a minute. According to De 

 Geer, Lyonnet, Bonnet, and other observers, the 

 lining membrane of these respiratory tubes (and 

 also of the alimentary canal) is cast off by cater- 

 pillars at the efioch in which they change their skins. 

 De Geer states that he has seen white fibres pro- 

 ceeding from the spiracles of a butterfly, attached 

 to the newly rejected pupa-case ; and he conjectures 

 that these fibres are really the delicate lining mem- 

 brane of the respiratory tubes, which are mounted 

 like the lining of the stomach of a lobster or cater- 

 pillHr. 



.Swammerdam in his description of the Rhinoceros 

 Vol, II. 



Beetle (Oryctes nasicornis) enters at length into this 

 wonderful exuviation. At Fig. 3387 are displayed 

 the exuviae and pulmonary vessels of the larva of 

 the rhinoceros beetle. A, a magnified view of a 

 pulmonary branch and vesicle ; a, a, pulmonary 

 branch composed of a membranous sheath and car- 

 tilaginous rings; B, the larva; c, c, nine reddish 

 spiracles or stigmata: C, the cast slough ofthe cater- 

 pillar, showing at d, d, the lining of the respiratory 

 tubes. 



With the function of respiration the circulation 

 of the blood is intimately connected. In most ani- 

 mals we discover a more or less perfect system of 

 bloodvessels, namely, arteries and veins, but in in- 

 sects a complete vascular system cannot be detected ; 

 not indeed that bloodvessels are wanting, for a dor- 

 sal vessel extending down the back is very appa- 

 rent, exhibiting a series of pulsations towards the 

 head, and in transparent caterpillars this vessel with 

 its pulsatory movements may be seen with the 

 naked eye. 



We may here observe that the chyle, or nutritive 

 portion of the digested food, appears to percolate 

 through the walls ofthe alimentary canal, filling up 

 every space internally, bathing the fine air tubes, 

 and thus subjected to the action of oxygen becom- 

 ing altered in character and analogous to the blood 

 of other animals. Such at least is the general 

 theory. 



Now to revert to the dorsal vessel. According 

 to Lyonnet this vessel contains a fluid, at first ap- 

 pearing colourless, but which when collected in drops 

 is found to be of a yellow tint more or less deep. A 

 powerful microscope shows it to be filled with glo- 

 bules of inconceivable minuteness. When this 

 fluid is mixed with water, the globules lose their 

 transparency and coagulate in small clammy masses, 

 which after evaporation become hard and brittle 

 like gum. The nature then of this fluid, and the 

 regular pulsation of this vessel, favour the idea of 

 the latter being a kind of heart. Swammerdam in- 

 deed asserts that he has seen tubes issuing from this 

 dorsal vessel, which he has succeeded in filling with 

 a coloured fluid ; but Cuvier and most writers have 

 stated that it is not only closed at each end, but that 

 there are no tubes leadinu; to it or issuing from it, as 

 is proved by the most elaborate researches. Lyon- 

 net, who traced the nerves and the ramifications of 

 the respiratory tubes of inexpressible minuteness, 

 could not detect, after the most painful investiga- 

 tions, either veins or arteries ; but the vessel appeared 

 to him to be open at the anterior end. 



Marcel de Serres states that the vessel can be re- 

 moved without causing the immediate death of the 

 insect ; and some physiologists have been inclined 

 to regard it as a secretory organ, but of what kind 

 it was impossible to conjecture. We do not think 

 this theory very tenable. 



According to Meckel, it is furnished with longitu- 

 dinal muscular fibres ; but Strauss Durkheim found 

 it, in the Chaffer at least, to consist of an outer mem- 

 brane, and an inner lining of circular muscular 

 fibres. Strauss Duikheim's description of this dorsal 

 vessel is very curious, and seems in some measure to 

 reconcile the conflicting views which have arisen 

 from the observations of other microscopic anato- 

 mists. This vessel, he states, is divided in thechaft'er 

 into eight compartments by a series of semi-lunar 

 valves, so constructed as to allow ofthe advance of 

 the fluid from the contraction of the vessel from the 

 tail upwards from the head, but not of its retrograd- 

 ing. At the anterior part of the vessel the fluid 

 issues through a perforation into the general cavity 

 of the body, and meanders in streams between the 

 various tissues ; but as at each contraction or sys- 

 tole the vessel exhausts itself, there must be some 

 means for keeping up a continual supply. It appears 

 that each chamber has a valvular orifice on each 

 side, communicating with the cavity of the body, 

 and the valves are so ordered as to permit the influx 

 of blood, but not the efflux ; hence, as the vessel 

 dilates after each contraction a quantity of blood 

 is sucked in, which, as it cannot return by the same 

 openings, must go forwards, from the structure of 

 the internal semi-lunar valves, and is thus kept in 

 perpetual circulation. Hence, therefore, though ex- 

 clusive of this long dorsal vessel there is no vascular 

 system, regular currents of the fluid, bathing the 

 viscera, the muscles, the airtubes, and other organs, 

 are maintained. Both the contraction and the dilata- 

 tion of this kind of heart begin from the posterior 

 chamber, and so upwards in rotation. The number of 

 contractions varies; they have been counted from 

 twenty to a hundred per minute. The extent and 

 divisions of this vessel differ in difterent insects. 

 Such is an outline of the account given by Strauss 

 Durkheim. 



More recently Professor Cams has published his 

 observations on the circulation, as investigated by 

 himself in certain very transparent insects ; and in 

 addition to the meandering streams evidently not 

 confined by vessels, he considers that there is also 

 a vascular circulation ; that besides the main cur- 



I rent discharged from the anterior orifice of the heart, 

 I " another portion of the blood is conveyed by two 

 lateral trunks, which pass down each side of the 

 body in a serpentine course, and convey it into the 

 lower extremity of the dorsal vessel from which they 

 are continuous." Dr. Roget, in his ' Bridgewater 

 Treatise,' figures this kind of circulation in the 

 sembla viridis, from a delineation by Carus in the 

 ' Acta Acad. Caes. Leop. Carol. Nat. Cur.,' vol. xv., 

 pt. II., p. 9. It appears that these lateral vessels 

 give oft' others, which in the form of loops supply 

 the antenna;, the tail, the limbs, and wings, and 

 return the blood to the lateral vessels, and these 

 again merge into the dorsal heart. A similar cir- 

 culation is asserted to exist in the Ephemera mar- 

 ginata, figured and described in Dr. Goring and 

 Mr. Pritchard's ' Microscopic Illustrations,' and fully 

 detailed and illustrated by Mr. Boweibank, with an 

 engraving on a large scale, in the ' Entomological 

 Magazine,' i. 239, pi. 2. 



With the respiration of insects is doubtless con- 

 nected many of the noises or sounds which they 

 utter during flight, and while at rest; and it is pro- 

 bable that they have the power of directing currents 

 of air to any special organ. Messrs. Kirby and 

 Spence consider that the vocal spiracles uf the Hy- 

 menoptera and Diptera are those behind the wings ; 

 we have indeed frequently held a fly, securing its 

 wings, and watched, as it buzzed, the rapid tremu- 

 lous vibrations of the alulae ; but when the wings 

 have been removed the cry was short and acute, 

 and it appeared to us that the full-toned buzz was 

 produced by the air driven against the edge of the 

 wings, in which, secured as they might be, there 

 was always a sensible tremor, that of tlie alulie 

 being more decided. The wasp-fly (Chrysotoxum 

 fascioJatum), Fig. 3388, is capable of buzzing when 

 at rest. 



The males of the crickets, grasshoppers, and 

 locusts (Orthoptera), produce their cry or chirp by 

 applying the hind shank to the thigh, and rubbing 

 it smartly against the wing cases ; but they have a 

 sort of drum or sounding-board " on each side ofthe 

 first segment of the abdomen, immediately above 

 the origin of the hind thighs ; it is in the form of a 

 large opening or pit, somewhat oval in outline, and 

 partly closed by an irregular flat plate or lid of a 

 hard substance, but covered by a flexible wrinkled 

 membrane. The opening left by the lid is- in the 

 form of a half moon, and at the bottom of the cavity 

 is a white membrane shining like a mirror and 

 tensely stretched. On each side of the opening 

 towards the head there is a small oval orifice, into 

 which the point of a pin may easily pass, and when 

 the membrane is removed a large cavity is brought 

 into view." The whole of this apparatus, says De 

 Geer, seems to contribute much to produce and 

 increase the sound caused by the insects. 



Fig. 3389 represents this apparatus : A, the first 

 ring of the abdomen magnified ; a, a deep cavity 

 partially covered by the plate b: B, the cavity with 

 the parts as they appear when the plate b is re- 

 moved ; c, the white membrane stretched across the 

 cavity ; d, the oval orifice. 



The field-cricket (Acheta campestris) is kept in 

 cages by the Spanish peasantry, who delight in its 

 querulous chirping. Our reader will remember the 

 quarrel between two boys respecting a cage full of 

 crickets which gave Don Quixote so much annoy- 

 ance, but which was ended by the squire making a 

 purchase of the chirping brood for four farthings. 



From time immemorial have the tree-hoppers,. 

 Cicadae, been celebrated for their music : — 



" Et cantu querulee rumpent arbusta dcad8e."^ViBoiL. 



The musical instrument of this species (order Ho- 

 moptera), the titt/J of the Greeks, has been de- 

 scribed by Reaumur. It is present only in the 

 male, and consists of two pairs of large plates, fixed, 

 to the trunk between the abdomen and hind legs.- 

 When this exterior membrane is raised, a cavity is. 

 exposed, part of which seems to extend into the 

 abdomen, and part to be covered with a second 

 membrane, much more delicate than the exterior 

 one, tensely stretched and iridescent ; in the middle- 

 there is a horny plate placed horizontally along the 

 bottom. All this, however, forms but a secondary 

 portion of the instrument, for the sound is in the 

 first instance produced by a bundle of muscular 

 strings, which are attached at one extremity to 

 another membrane in the interior, obviously the 

 true drum ; for when Reaumur pulled these strings 

 and let them go, the sound was produced for some 

 time, even after the death of the insect. These 

 muscles, he slates, are so attached to the under 

 concave surface ofthe drum, that when they pull it 

 downwards and let it jerk quickly back again, a 

 vibration is produced, and the sound issues through 

 an opening like that of the larynx of quadrupeds, 

 or the sound-hole of a violin. 



Fig. 3390 displays the under side of a cicada with 

 the external plates visible. 



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