INSECTS. 



u- infe(£ts they are only four in number, large, undulated, called abforbents, in the four firft clafles of the animal king- 



ig as the body, and of an oranjre colour. dom ; thefe convey it into the blood-vcffels, in which ft 



Among the neuroptera, the libeiliilx have a confiderable pafFes to all tlie organs of the body. The application of 



i.ber of ihort ones, fnrrounding the inteftine at a I'mall the new matter furnifhcd by digelHon to the parts of the 



.. nee from the anus, where it becomes large. The fame fyllcm is performed in fome other way in infeds, as they 



idure exilts in the common grylli. In the gryllo-talpa feem to have neither abforbing nor blood-veflels (excepting 



;.._ie isa large packet of thefe velfels, terminating bya com- the cruftaceous infefts). 



nion canal in the middle of the large inteftine. Tlie larvx Cuvier is of opinion that the nutritive procefs is performed 



and the perfect infefts have the fame llriiclure in thefe genera, in this clafs by imbibition. We arrive, fays he, at this con- 



Tliisrefemblance feems moreover to exilt, with refpect to the clufion by proofs of different kinds ; fome arc direft, but 



hepatic organs, even in orders where the metamorphofis is the negative; other.-; fupply only indnftions ; their union will 



molt complete in all other parts; the number at Icail is not probably fufEce to grodnce conviftion. In the firft place, 



t'lj.ngcd. It is confiderable in the hymenoptera, but ge- he continues, no veffels are found in diffefting infects ; I 



. ly amounts only to two in the coleoptcra. In the latter have fought for them with the greateit attention, and by 



are generally found parallel to the uiieftinal canal, and the afliitance of the microfcope, in thofe organs, which in 



i^^e numerous windings. Their infertion is immediately other claflTcs contain them in the greatert abundance, as the 



;L*tcr the ftomach in the larvK of the fcarabsei, the dytifci, choroid coat of the eye, and the membranes of the intelHnal 



the carabi, &c. canal ; I have never found any thing like them, although 



The caterpillars and the peifeft infefts produced from the trachea: and the nerves are very eafily difcovered, and 



tliem have two, each of which is fub-di\aded into three, the innumerable ramifications of the former may be traced 



placed in the former, at the fides of the polleriorhalf of the with the naked e^e. Lyonet, who has defcribed and repre- 



caiial, and forming their principal folds completely in the fented in the larva of the coflus parts a thoufand times fmaller 



back of the body. Among the hemiptera, the nepae feem than the principal blood-vetTels would be, could never dif- 



to have only two. The larva; of the ftratyomys and fyrphus, cover anything of that kind. 



of the order diptera, have four, which end in the inteitine by There is indeed in infefts an organ, to which many ana- 



a common trunk. tomifts have given the name of heart ; it is a membranous 



Coverings and Supports of the Alimentary Canal. — We have tube, continued through the whole length of the back, 



mentioned already that the ftomach of the cruitacea is fup- both in the larva and in the perfeft Hate, exhibiting alternate 



ported in its fituation by its mufcles ; the remainder of the contraftions and dilatations, which feem to pafs fucccfllvcly 



canal is maintained only by vefiels, and by the compreffion from one extremity to the other ; but, notwithftanding this 



of the furrounding parts. circumltance, which feems to indicate an organ of circulation, 



In the proper infefts, the inteftinal canal is retained in its this tube produces no branches, and we can neitlier attribute 



place by the trachex only ; there is neither mefentery veflel to it the funftions of a heart, nor difcover any other purpofe 



nor cellular fubftance ; confequently when an infeft is opened to which it is fubfervient. La.lly, thofe naturalilts who 



and placed in water, all the folds of its canal rife, and are de- have obferved with the microfcope the tranfparent pai cs of 



veloped from the fpecific tightnefs derived from the air in the infefts, have difcerned only a fluid at reft, bathing them on 



trachejE. all fides. 



The fine membrane lining the abdomen, and enveloped by Such are the negative arguments on this fubjcft ; thofe 



the rings of the Ikin and their mufcles, may be called peri- drawn from induftion refer principally to two points ; -viz. 



toneum. the mode of refpiration in infefts, and the form of the fecre- 



But the moft remarkable circumftance belonging to infefts tory organs, 



in their larva ftate, and exifting in them exclufively, among In animals which have a circulation, it is continually 



all invertebr?.! animals, is the portions of cellular texture collected in a central refervoir, whence it is forcibly expelled 



filled with fat, which may be compared to omenta, and may to all parts ; it always arrives at the organs from the heart. 



Lave the fame funftions. They feem particularly defigned and it is always fent to the heart before it comes back again. 



to fupply the materials of liutrition to the animal, during all It may then have been modified from its fource by the action 



that time, in wliich, as a chryfalis, it eats nothing, as the of the air ; and, in faft, before it is brought by the aorta 



fat of .the omenta fupports life in thofe quadrupeds, which and its ramifications to the parts which are to be nourifticd 



pafs the winter in a lethargic fleep. When the animal by it, it circulates through the lung or gills. If this ar- 



changes its coverings and its form, and becomes a perfeft in- rangement is not found in infefts, tlie reafon probably is 



feft, thefe fatty organs probably furnifli the prodigious that their nutritive fluid is not contained in veifel;, that it 



quantity of materials, which the fuddcn developement of fo does not come from a common fource, and confequently that 



many parts muft require ; confequently they arc not found it could not undergo any modification in a feparate organ 



in the latter ftate. before arriving at the parts. It continually and quietly 



The forms, colour, and confiftence of theL- mafles vary, bathes all the parts, which are to draw from it fubftances 



In the caterpillars they are oblong, fwoilen, full cf a white fuiied to their wants ; the aftion of tlie air (liould therefore 



fat like cream. In the larvse of the fca; abcei they are large reach it every where, and this point is very completely fecured 



femi-tranfparent membranes, with many opaque and white by the difpnfition of thetrachese, as there is no point of the 



grains ; in thcjie of the flies and ftratyomys they have a body to which the fine ramifications of thefe vefllls do not 



Ilalhed appearance, lik-? narrow ribbands irregularly joined, penetrate, and where the air does not immediately excrcife 



They are incoufiderable, or do not exill at all, in llie larvas its chemical aftion ; in a word, as the blood cannot go in 



of infefts, which undergo an incomplete metamorphofis, foarch of the air, the air is every where brought in coiitact 



which eat during their whole exiftence, and never pafs into with the blood. 



the chryfahs ftate. In all the orders they receive nunierous The fecretions oL«nfefts are never performed by conc;lo- 



air-veffeis. merate glands ; their organs confift, in all cafes, as we have 



Abfirption in Injects. — The nutritive fluid prepared in the juil feen in the example of the liver, of long and (lender 



alimentary canal is taken up by a particular .order of veffels, tubes, floating in the cavity of die body, without being con- 



nefted 



