INSECTS. 



fomctimes by one or two tubes opening into the anus. The 

 latter ftruclure belongs to the true aquatic infefts ; fome of 

 which, as the larvx and chryfahdes of the hbelhiliE, have in 

 the rcftum a particular apparatus for this purpofe, which 

 we (liall defcribe. 



The trachejE of the larvx do not refetnble thofe of the 

 perfe£l infefts any more than the other organs : indeed the 

 differences in this refpcft are often ftill more furprifing. 



We (hall defcribe the organs fucceffively in the mod re- 

 markable families. 



Thofe of the caterpillars are the beft known, through the 

 admirable defcription given by Lyonet of that infeft. A 

 nearly cylindrical tube, receiving air by ten ftigmata, ex- 

 tends on each fide of the body. Its branches go off in a 

 radiating manner, from points exactly correlponding to the 

 fligmata ; thofe at the beginning, wliich go to the head, are 

 larger than the fucceeding ones. We obferve here, once for 

 all, that no" part is unprovided with thefe air-vefiels, and 

 that the very membranes of their trunks even receive 

 fmall branches. In the caterpillar they are ftrong, opaque, 

 and of a fine filvery colour, which, however, depends in part 

 on the contained air ; for the brilliancy is loft, both here 

 and in other families, when they are macerated and filled with 

 water or fpirits of wine. The air-veffe'.s of the butterflies, 

 produced from thefe caterpillars, have a very different ap- 

 pearance ; they are thinner, lefs numerous, and pofiefs al- 

 moft throughout fmall yellow or white elliptical bodies of a 

 fatty nature : fuch at leaft is their appearance in the atalanta 

 and the phalsna pavonia. 



A much more confiderable change is obferved in the cole- 

 optera lamellicornia : the larva has fafciculi of cylindrical, 

 filvery, and v^ry fine tracheae, diltributcd from each ftigma 

 over the furrounding parts. In the perfect mfeft they are 

 of a dead white, fwelled every where into imall oval or irre- 

 gularly-figured veficles, with very thin fides : they refemble 

 trees much loaded with leaves. Examples of this arrange- 

 ment may be ken in the mclolonthiE, the fcarabasi, the co- 

 prides, the lucani, &c. : and it occurs in ne other families. 



The hymenoptera and the diptera have two large veficles 

 at the bnfis of the abdomen, and fome Imall ones : but the 

 number is always inconfiderable. 



The hydrophilus piceus has four large ones at the bafis 

 of the abdom. n ; and, as this is a lliriftly aquatic infeft, they 

 may aflill the animal, as the fwimming-bladder of filhes does, 

 in railing or dej'refling itlelf in the water. 



The principal air opening in the aquatic larvx is generally 

 near the anus, that they may the more readilv reach the air : 

 in this cafe the two lateral trunks of the tracheae are of great 

 fize, apparently for the purpofe of holding a larger fupply 

 of the fluid ; and the branches go off in the form of flender 

 cylindrical threads. This arrangement is found in the larva: 

 of two very different families, the hydrophilus and fl:raty- 

 omys. The latter, as all the aquatic larvae of the diptera, 

 can elongate its tail confiderably in fearch of air without 

 elevating the body ; the anus is furrounded by fmall trachex 

 in the form of radii. Thefe infedts fufpend themfelves at 

 the furface of the water by means of their tails. 



The larvx of the libellulx exhibit the moft fingular dif- 

 poiition of the refpiratory apparatus. The orifices, which 

 abforb the air, arc found in the reftnm, under the form of 

 very fmall tubes, ranged in little groups in ten rows, which 

 reprefent fo many long pinnated leaves. A number of 

 fmall trachex, equal to that of the tubes within, pafles from 

 the rcftum into the body; and thefe terminate in four 

 trunks extended through the whole length of the body. 

 Two of thefe are of vaft fize, and appear to ferve as refer- 

 vojrs ; for they fend the air which they contain by tranfverfe 



branches into the other two fmaller trunks, which proc 

 as ufual along the fides of the body, and fupply all y 

 with air-yeflels. Each of them produces a recurrent bra i, 

 which, after having crofled the correfponding one, proct t > - 

 along the intefl:inal canal, and gives it an infinite number d 

 fmall ramifications. Cuvier thinks that the air contained i:; 

 thefe different trunks follows a determinate courfe, relativr 

 to the occafions of the parts to which it is diftributed. '1 hi- 

 four trunks and the two recurrent branches are found in the 

 perfeil libellula ; bnt they no longer derive their air fr.,n 

 the anus. As the animal hves in the atmofphere, its trachei 

 are fupplied from ftigmata, near each of which is a veficlc, 

 ferving probably as a refervoir. There is alfo a fingle row 

 of larger veficles along the back. 



The trachex appear to be deficient in fome infefts, that 

 is, in the arachnida, where we have ftated that fomcthing hke 

 a heart is perceptible. There is however a fingle ftigma at 

 the bafis if the abdomen in the fpider : but it leads only 

 into a veficle, from which no air-veffels have been traced. 

 Can this be the lung i and are there blood-veffels diftributed 

 on its fides ? 



Organs of the Voice. — By the voice we underftand the 

 found produced by animals in expelhng air from their lungs, 

 through the glottis: in tliis fenfe it can be pollcfTed by thofe 

 animals only which have lungs, as the mammalia, birds, and 

 reptiles. Several infers produce founds, and often very 

 confiderable ones, by the motions of various parts of their 

 body : but there are no exprefs organs for this purpofe. By 

 thefe founds they invite each other, and exprefs their wants 

 or their paftions. 



Organs of Generation. — Many very ftriking peculiarities are 

 obferved in the propagation of infedls. Tiie two fexes of 

 one and the fame fpeeies are often fo extremely unlike each 

 other, that they would rather be taken for completely dif- 

 ferent fpccies, than for animals that could pair together. 

 Among the bees and other neighbouring fpecies, the greateft 

 number of individuals have no fex ; they arc conceived and 

 bcrn without being deftined, as in the ordinary courfe, to 

 conceive or produce impregnation. Their copulation is per- 

 formed in a very extraordinary manner in many inftances. 

 The adl is performed on the wing, and iome arc winged only 

 during the fitort feafian of copulation. Several copulate 

 only once, and the aft is very foon followed by death : the 

 life of the animal may be prolonged by deferring the copu- 

 lation. 



In feveral, as the cochineal infeft (coccus cafti), and the 

 chigger (pulex penetrans), the pregnant female increafes to 

 an enormous fize. The abdomen of the white ant (termes 

 fatalis), when ready for laying, is calculated to be two thou- 

 I'and times larger than it was before impregnation. 



Organs of Generation in the Crujlacea. — Thefe among the 

 invertebral are what ferpents and lizards are among the ver- 

 tebral animals; their exterior organs are double; but, which 

 is peculiar to themfelves, their internal organs, both tefticles 

 and ovaries, are fometimes united into one. 



The decapoda in general have two penifes and two vulvx: 

 the openings of the latter are found at the bafis of the third 

 pair of feet. The two penifes are quite at the back of the 

 thorax, behind the fifth pair of feet : in this fituation there 

 is, on each fide, a horny, pointed, tubular piece, opened 

 longitudinally, which may be introduced into the vulva, and 

 condufts the penis which palFcs through this tube. We fee 

 in the male, on the infide, two very tortuous vafa deferentia, 

 each of which is continued to the root of the penis of its 

 own fide. In the lobfter and cray-fifli the two canals proceed 

 from a tefticle divided into fix lobes, lituated under the heart, 

 behind the ftomach, and between the two maflTes of hepatic 

 1 1 veflTels- 



