842 



MUSEUM OF ANIMATED NATURE. 



fiNSECTS. 



Fig. 3391 shows a a, the outer drums ; b, the 

 muscular strings ; c c, the inner drums. 



The Fulgora laternaria of Guiana, an allied form, 

 makes a noise at night so loud and disagreeable as 

 not unfreqiiently to prevent repose. 



Among British insects which utter singular noises, 

 may he noticed that fine species of moth, the death's 

 head hawk-moth (Acheronta atropos), of which we 

 have a pictorial specimen at Fig. 33^2. 



The cry uttered is a sort of squeak, like that of 

 a mouse, loud, distinct, and piteous. From this cry 

 and the singular markings of the thorax, it has 

 been an object of popular superstition both in our 

 own country and the Continent. The mode in which 

 its cry is produced has puzzled numerous investi- 

 gators, and various and even contradictory expla- 

 nations have been given, as the result of experiment 

 and observation. Reaumur concluded the noise to 

 be produced by the friction of the palpi against the 

 proboscis, and found, he says, that when he uncoiled 

 the spiral proboscis with a pin, the noise ceased, 

 but was renewed when suffered to curl up again. 

 He found also that by preventing the palpi from 

 touching the proboscis, he could stop the sound. 

 These experiments are represented at Fig. 3393 ; a, 

 the proboscis secured; b, the palpi secured. On 

 the contrary, we learn that after the extirpation of 

 these parts, as tried by M. de Johet, the noise con- 

 tinued to be produced, accompanied by a shivering 

 •f the wings, under which, at their base, the expe- 

 rimenter found two scales, and these being cut 

 away the insect became mute, and he attributes the 

 cry to the action of the air forced out of spiracles 

 against these scales. M. Lorrey again says that the 

 sound arises from air escaping rapidly through 

 peculiar cavities on the sides of the abdomen, fur- 

 nished with a fine tuft of hair and communicating 

 with the spiracles. MM. Passerini, Duponchel, 

 and DumcSnl, attribute it to the impulsion of air 

 into a cavity of the head, furnished with muscles 

 and a sort of tympanic membrane. According to 

 Mr. Kaddon this moth is able to produce the sound 

 before quitting the pupa-case. That it is con- 

 nected with the respiratory organs, we think there 

 is little doubt, but the peculiar mechanism by which 

 it is caused' seems to be as yet unascertained. We 

 say nothing here of the noises which insects make, 

 by means utterly unconnected with their respiratory 

 system, as the tick of the anobium or death-watch, 

 produced by the insect rapping with its head against 

 woodwork, into which it bores, or of the timber- 

 louse (Atropos pulsatorius). 



We shall here say but little of the nervous and 

 muscular system of insects. With respect to the 

 former we need not repeat that it is ganglionic ; but 

 we may state that during the progress of the insect 

 from the larva to maturity it undergoes certain 

 alterations. In the larva the ganglia are numerous 

 and small, and too feeble to animate powerful 

 limbs or receive lively impressions. As the growth 

 of the larva brings it towards the pupa stage, the 

 nervous centres begin to concentrate themselves, 

 several of the ganglia coalescing, and the nervous 

 chords connecting them becoming flexuous. In the 

 pupa this modification is very palpable, and at the 

 same time the wings and limbs with their muscles 

 begin to develope ; this concentration goes on till 

 the insect is about to emerge in a perfect state, but 

 varies in ratio according to the organic elevation of 

 the insect in its class. Fig. 3394 shows the nervous 

 system in the perfect chaficr-beetle, and in a cater- 

 pillar or larva. 



With regard to the muscles of insects, we may 

 conceive that they are well developed and endowed 

 with great vigour when we reflect on the surprising 

 leaps some species are capable of making, and of 

 the untiring flight or aquatic movements of others. 

 It has been calculated that the chaffer-beetle is 

 proportionally six times stronger than a horse. 

 The number of the muscles in these creatures is 

 astounding. Lyonnet counted in the head of the j 

 caterpillar of the goat-molh two hundred and ! 

 twenty-eight ; in the body, one thousand six hun- 

 dred and forty-seven ; and around the alimentary 

 canal, two thousand one hundred and eighty-six ; 

 deducting twenty as common to the head and body, 

 the total number is four thousand and sixty-one. 

 Of the arrangement of these muscles some idea may 

 be formed by referring to Fig. 3395, a magnifieii 

 view of the principal dorsal muscles of the cater- 

 pillar in question (Irom Lyonnet). 



Fig. 3396 represents the same species of cater- 

 pillar escaping irom under a loaded glass. 



We may now proceed to glance at the digestive 

 apparatus of insects, premising that they possess both 

 salivary and biliary organs, and that saliva and bile 

 are abundant. As in other animals, we naturally 

 anticipate modifications of the nutritive appara- 

 tus according to the nature of the food; and that 

 in the voracious caterpillar which devours the leaf, 

 there must occur a great change, in order to fit it 

 for a new existence, when it flits a winged butter- 

 fly, sipping the nectar of flowers. 



In mandibulate insects, as the beetle, the gullet 

 leads to a crop entering a muscular gizzard resem- 

 bling that of a fowl, lined with a strong membrane ; 

 and sometimes studded with horny plates, or even 

 curved teeth for grinding and tearing. To the giz- 

 zard succeeds a true stomach, at the pyloric end of 

 which the biliary vessels, usually four, six, or eight 

 in number, enter. To the stomach succeed the 

 small intestines of varying length, and sometimes 

 not to be distinguished from the large intestines. 



In the haustellate insects, as the butterfly, and 

 also in the bee, there is no gizzard, but a honey- 

 crop : in the bee it is a simple distention of the 

 oesophagus, but in the butterfly, rt is a sac with a 

 narrow neck. The salivary and biliary vessels are 

 long slender tubes convoluted together. There are 

 no absorbents or lacteals on the inner surface of the 

 alimentary canal, as in higher animals ; but the 

 nutritive juice appears to transude through the 

 coats of the intestine into the cavity of the body, 

 where it becomes mixed with the blood. 



Fig. 3397 shows the alimentary canal of the 

 Cicindela campestris, a carnivorous beetle : a, 

 oesophagus ; b, crop ; c, gizzard ; d, stomach ; e, e, 

 biliary vessels : /, intestine. This is very simple, 

 but we find it still more so in the plant eating cater- 

 pillars of the moths and butterflies, which in the 

 course of a month devour about 60,000 times their 

 own weight of aliment, and in which the stomach is 

 of enormous volume. Figs. 3398 and 3399 represent 

 respectively the upper and under surface of the 

 digestive organs of the viscera of the goat-moth : A, 

 B, C, the oesophagus and its appendages ; D, E, the 

 stomach, embraced by a pair of spiral muscles 

 which act upon it ; it merges into a simple large 

 intestinal tube, F, G, H, receiving at G the biliary 

 vessels, I, I, the convolutions of which surround it. 

 Figs. 3400 and 3401 represent respectively the 

 caterpillar and the alimentary viscera of the Tor- 

 toise-shell Butterfly (Vanessa Urticae). A, the 

 caterpillar magnified ; a, k, the alimentary viscera ; 

 a, the gullet ; b, b, respiratory tubes ; c, ligament of 

 the stomach ; d, d, annulations of the same ; e, e, 

 coils of biliary vessels ; /, their entrance ; g, g, h, h, 

 their folds ; t, k, intestine. 



Fig. 3402 represents the changes that take place 

 during the progress of the caterpillar to the butterfly, 

 in its digestive apparatus. A, Caterpillar ; a, oeso- 

 phagus; J, stomach ;c,d, intestinal canal. A, pupa 

 two days old, parts lettered the same. B, Pupa 

 eight days old ; a, dilatation of CBsophagus, form- 

 ing the honey crop. D, Pupa immediately before 

 its transformation. E, Butterfly ; a, honey crop 

 fully developed. 



Let us now pass to subjects more interesting 

 generally than the points of structure just noticed ; 

 viz., to the senses of insects and their respective 

 organs. 



Sight. — If one part more than another in the 

 structure of insects is calculated to excite our aston- 

 ishment, it will be the structure of the organs of 

 vision, in which a world of wonders is included. 

 We may premise by observing that in the Crustacea 

 the eyes are modelled upon the same general plan 

 £is those of insects, and that we purposely deferred 

 saying any thing respecting them till the present 

 opportunity, as our pictorial illustrations refer to 

 the eyes of the latter class. 



The eyes of insects are not moveable in a socket 

 or orbit, as those of quadrupeds and birds ; they are 

 either simple or compound, and in most insects 

 both are present. The simple eyes are termed 

 stemmata, and are usually three in number, placed 

 so as to form three points of a triangle on the 

 top of the head or the space behind the inser- 

 tion of the antennae. Often, however, these simple 

 eyes are not isolated ; in this case they are numer- 

 ous, and collected into groups, the number of which 

 varies. A simple eye consists of a convex smooth 

 transparent cornea, behind which is a globular lens 

 supported by a vitreous humour, upon which the 

 retina is expanded. The whole of this is enclosed 

 in a layer of brown, red, or black pigment, which, 

 advancing on the lens, forms a distinct iris, with a 

 central opening or pupil. These eyes appear to be 

 appropriated to upward vision, and bees in which 

 they have been varnished, appear to lose their 

 way. 



The compound eyes are generally two in number, 

 one on each side of the head, and mostly, as in the 

 common fly, the dragon-fly, and others, occupy con- 

 siderable space ; in large insects their facets may be 

 seen even without the aid of a microscope. Fig. 

 3403 represents the eyes of — a, a worker bee ; 6, a 

 male bee. The simple eyes orstemniata form three 

 points of a triangle. If we take a common house-fly 

 and examine its large eyes through a tolerably good 

 glass, we shall find these organs to present a regu- 

 larly tesselated surface, which is indeed made up 

 of a multitude of hexagonal facets divided from 

 each other by distinct partitions. Each facet is the 

 cornea of a distinct eye provided with its own nerve, 

 retina, lens, iris, and pupil. In the fly four thou- 



sand of these eyes (ocelli) maxe up the whole com- 

 pound one (oculusj. In some diagon-flies there are 

 twelve thousand. Butterflies have upwards of seven- 

 teen thousand, and some coleoptera have more than 

 twenty-five thousand. To such gifted beings the 

 fabled Argus must yield the palm. 



Though generally insects possess only two of these 

 multi-ocellaled eyes, yet in some there are four, as 

 in the genus tetrops, in which the facetted eyes are 

 two on each side ; and it appears that the males of 

 some of the Ephemerae have, besides the ordinary 

 simple and compound eyes, a pair of additional com- 

 pound eyes, on the top of a columnar projection. 

 Fig. 3404 represents, a, the Tetrops prasusta, a British 

 beetle, and b, the two eyes, or rather the divided 

 eye of one side greatly magnified. Fig. 3405 shows, 



a, the large eyes of the whirlwig (Gyrinus natator), 

 placed partly on the upper part of the head for see- 

 ing above, and extending underneath the head for 

 seeing in the water below; 6, the additional eyes 

 of Ephemera, greatly magnified. Fig. 3406 shows 

 the eyes of the bee liighly magnified at A ; a, the 

 eye in its perfect state, covered with the cornea; 



b, an eye from which the cornea and some of the 

 hexagonal facets have been removed to show its 

 structure ; c, the three stemmata or simple eyes; d, 

 the ganglion of the optic nerve. B, a portion of 

 the surlace of the eye deprived of its cornea : C, the 

 saine covered with the cornea, showing the hairs 

 which spring from it. 



These organs have been diligently investigated 

 by many microscopic anatomists, as Hook, Leeuwen- 

 hoek, Miiller, Duges, and Strauss Durkheim. Ac- 

 cording to the latter, the hexagonal facet or cornea of 

 each ocellus is a double convex lens, and behind it 

 is placed a hexaijdral transparent prism analogous 

 to the vitreous humour. Llpon the posterior part 

 of this the optic nerve terminates in a minute pyri- 

 form bulb ; at which point a layer of pigment forms 

 a choroid tunic. With respect to the optic nerves 

 it may be observed that they originate from a com- 

 mon ganglion, derived itself from the supraoesoplia- 

 geal mass; from this common ganglion arise a num- 

 ber of short nerves, which soon unite and form what 

 Strauss Durkheim calls the common or general 

 retina; and from this nervous expansion, multitudes 

 of minute nerves diverge to their respective ocelli, 

 first passing through a layer of pigment, of ditfeient 

 tint in different insects. Each of these minute fila- 

 ments forms, as stated, at the back of its respective 

 ocellus, a special retina of a pyriform figure. 



It cannot be doubted but that there are many 

 modifications in the structure of these organs, and 

 from this circumstance, as well as from the miiiute- 

 n«ss of the eyes themselves, some discrepancies may 

 be expected in the descriptions given by diti'erent 

 observers. 



Duges describes the eye of the Dragon-fly as fol- 

 lows : — Each ocellus consists of what he terms a 

 transparent ' corneule,' convex anteriorly, concave 

 posteriorly, but with the concavity less than the 

 convexity. The opaque pigment which invesis each 

 ocellus forms a sort of ins at the back of the ' cor- 

 neule ' with a central pupil which transmits the rays 

 of light to a transparent cylinder filled with a vitre- 

 ous humour, and to this cylinder runs a filament 

 from the optic ganglion direct, without any general 

 retina being formed as described in the Chatter by 

 Strauss Durkheim. 



Duges notices a small space at the back of each 

 corneule, filled with aqueous humour. Fig. 3407 

 will serve to render the above brief description in- 

 telligible. It is a supposed section of the eye of the 

 Dragon-fly. a, a, the corneules, behind which is a 

 layer of black pigment, c, c; then follows a tinted 

 zone e, consisting ol transparent vitreous cylinders, to 

 which pass the nerves j, through a dark pigment , each 

 nerve radiating from the optic ganglion;. Fig. 3-lOS 

 represents the eye of the Stag-beetle (LucanusCer- 

 vus), in which the cornea, a, is of extraordinary 

 thickness, each corneule being so much elongated 

 as to appear prism-like. 



Fig. 3409 shows the mode in which the rays of 

 light may be supposed to impinge on the ditfeient 

 corneules or facets. Mr. Parsons, whose iiliislra- 

 tions and details we follow, savs, — " If rays olditler- ' 

 ent colours given out from tlie points a, b, c, d, fall 

 upon the eye, the cone h will be iilununated 

 throughout its whole length by the ray d', which 

 traverses this cone in the direction of its long axis ; 

 the other cones, situated in the vicinity of the line 

 m, d, will not be illuminated as far as their internal 

 extremity by the rays from d, which penetrate less 

 and less deeply into the neighbouring cones, in pro- 

 portion as they become more remote Irom the line 

 m, d. The nervous filament w, corresponding to 

 the cone h, is consequently impressed with the ray 

 d' ; the other rays from d, being absorbed by the 

 pigment investing the neighbouring cones, will ot 

 course produce no ett'ect on any nervous filament 

 placed out of the line 7n, d. The coloured ray d' is 

 therefore perceived only by means of the filament 

 m, on wliich latter alone it impinges. So also the 



