INSECTS. 



Be exercifed by other parts. The organ which is commonly 

 confidereJ as the tongue of infefts, merely ferves for taking 

 in the food. But the accurate obfervations of profelTor 

 Knoch, (in his Contributions to the Knowledge of Infefts, 

 in German,) renders it very probable, that the pollerior 

 pair of palpi, or feelers, pofTefies the power of tafte in feveral 

 of this clafs. 



Numerous fafts have long ago proved, that fcvcral infecls 

 can dillinguifii the odorous pi-operties of bodies, even atcon- 

 fidcrable dillances. But the organ in which this fenfe 

 refuk-s, has not hitherto been clearly pointed out. Since 

 all red-blooded terrellrial animals fmell only through the 

 medium of the air wliich they take in in infpiration, feveral 

 naturaliils have fuppofed, that the iligmata of infefts are to 

 be confidered as organs of fmelling. Others afcribe this 

 office, and with fome probabi.ity, to the anterior pair of 

 palpi. 



There is no doubt that feveral infefts pofTefs the fenfe of 

 hearing, but the organ of this fenfe is very doubtful. In 

 fome of the larger animals ot the genus cancer, a part can 

 be dirtinguilhed which feems to be analogous to the vefti- 

 bulum of the former clalfes. A fmall bony tube is found 

 on each fide at the root of the palpi ; its external opening 

 is clofed by a finer membrane ; and it contams a membranous 

 lining, on which a nerve, anfing from a common branch 

 with that of the antenm, is expanded. The latter circum- 

 ftance might favour an opinion, that the antennae themfelves 

 are organs of hearing: but this is refuted by confidering the 

 exquifite fenfe of hearing, which fome infefts pofTefs, who 

 have no true antennje, as the fpiders ; and by experiments 

 on others, which (hew that the fenfe of hearing is not 

 weakened by removing the antennx. 



The compound eyes and the Itemmata have been defcribcd 

 in the article Extomology. The former are found in dif- 

 ferent numbers in moft of the aptera, as alio in the larvx 

 of many wmged infefts. When thefe undergo the laft or 

 complete metamorpholis, and receive their wings, they gain 

 at the fame time the large compound eyes. Several genera 

 of winged infedls, and aptera (as the larger fpecies of mo- 

 noculi) have ftemmata befides their compound eyes. Far- 

 ther inveftigation is neceffary to fhew how thefe eyes enable 

 the infeft to fee ; and to determine the dillincilions between 

 two fuch very different organs. Blumenbach confiders that 

 the ftemmata are defigned for feeing near objects, and ihe 

 polyedrous eyes for dillant ones ; becaufe butterflies have 

 the latter only in their winged or perfetl ftate, while in the 

 caterpillar ilate they have only ftemmata. He acknowledges, 

 however, that this opinion is very doubtful, becaufe fome 

 infects, which live completely underground, as the mole- 

 cricket (gryllus gryllotalpa, Linn.) have both kinds of 

 organs. 



On the organs of the fenfes in this clafs, the reader may 

 confult Lehmann, de fenlibus externis animalium cxfan- 

 guium: conunentatio premio regis ornata, Ooctting. 1798, 

 4to. F. J. Schelver verfuch einer naturgefchichte der finnes 

 werkzeuge bey den Infecten und Wiirmern ; EfTay towards 

 the Natural Hiilory of the Organs of Senfe in Infcfts and 

 Vermes ; Goctling. 1798, 8vo L' hmann de antennis in- 

 feftorum, 1799, 8vo. Knoch's neue beytrage zu der 

 Iniectenkunde ; Contributions to the Knowledge of Infedls. 



Organs of the dlgejlive Funllions. — For a general account 

 of the pans about the mouth and their nomenclature, fee 

 Entomology. 



Jaws of the Crujlacea. — Moft of the genus cancer have at 

 their nwutii live or fix pairs of organs, which mult be re- 

 garded as ja vs, fince they move lateraHy in a horizontal 

 plane ; they are placed fucceffively one over the other, and 



the moft exterior has becii called by fome anat»mi(ls the 

 hp, but wrongly ; fince it is not fingle, and the two parts 

 which compofe it have lateral motion like the others. All 

 thefe jaws are articulated under the thorax, anteriorly with 

 refpeA to the feet, of which tlicy feem to continue the f'.'ries 

 in froi;t ; and each of them has, on the inner fide of its root,- 

 a membranous plate, which, flipping under the lateral bcrder 

 of the thorax, between the anterior branchix, ferves to fepa- 

 rate their lobes, and to comprefs tiicm in the aft of refpiratiori. 

 The feet have fimilar laminx for the pofterior branchix, but 

 they' are deficient in thofe fpccies which have the brancluje 

 under the tail, as the fquilla. (Fab.) 



Thefe jaws, with the exception perhaps of the one or two 

 moft interior parts, are formed of two divifions ; of one, which 

 may properly be celled the jaw, and anotiicr, which is its dor- 

 fal palpus or feeler. The hitter is more elongated, and ter- 

 minates in an articulated and pointed thread : the other has 

 at its end, but in the two firit pairs only, a feeler which does 

 not end in a pointed brillle like the other. This arrange- 

 ment is common to the crab, lohfter, cray-fifli, hermiteral, 

 and, in general, to all the cru'.lacea decapoda of Latreille. 

 In the firft the outer jaw is flattened, and joined fo well to 

 the correfponding piece and to its feeler, that the four pieces 

 together form a kind of fliieM, which covers all the other 

 jaws. But in the lobfter and cray-filh the outer jaw is prif- 

 matic and ftrong ; and the divifions of the fce'er being nearly 

 as large as the body of the jaw, the whole together refem- 

 bles a foot, and has often been defcribed as fuch by the 

 ancient naturalifts. 



In the cruftacea decapoda, the fecond jaw, reckoning from 

 the outer one, refembles the firft, whatever may be its form, 

 except that it is fmaller, and that its inner edge is extenuated 

 and ciliated, inftead of being denticulated. The body of 

 the third is divided into two lobes, the fourth into four, and 

 the fifth into two ; all thefe three are thin and ciliated. 

 The palpi of the two latter have generally a fimple point in- 

 ftead of a thread. The fixth is merely a fmall, oval, mem- 

 branous plate, %vithout cilia or palpus. Some varieties are ob- 

 ferved in the number and figure of the jaws in the cruftacea. 

 Tiius, among the decapoda, the fcyllarus (Fab ) has no 

 thread-like procefs on the dorfal piece of the two firft jawS-; 

 the third is undivided, and the fourth only divided into two 

 without a dorfal piece in either. Tlie fifth and laft is the 

 ufoal fmall oval plate. Among the branchiopoda there are 

 ft ill more remarkable differences : in the fquilla (Fab.) the 

 two firft jaws are extremely flender and elongated, have the 

 form of feet, and are terminated by a dilated rounded arti- 

 culation, and a moveable hook. They really perform the 

 office of feet, and not of jaws, and have no dorfal palpi. 

 The third is a long plate, with three notches on its inner 

 edge. The fourth is bifid ; its inner lobe is ciliated ; the! 

 external is pointed, and has on its dorfal furface a fmall oval 

 palpus of a fingle articulation. The fifth and laft is a 

 fimple plate. 



Notwithftanding all thefe varieties, it is ftlll true that all 

 the cruftacea have many pairs of jaws, very different from 

 each other in their funftions ; and that thefe organs muft 

 aft on the food, and prepare it for the proper maftication in 

 a peculiar manner. In faft, over all thefe organs are found 

 the true mandibles, which are very ftrong in all the genera. 

 The trituratin,; part varies in form. In the lobficr and cray- 

 fifli there is on tlie infide a blunt and truly molar furface, 

 and on the outfide a cutting edge divided into three rounded 

 denticulations. In the hermit crab the denticulations arc 

 pointed and feparate. In the crab there is a continuous 

 cutting edge. The fcyllarus (Fab.) has two feparate den- 

 tjculations ; a pointed one in front, and a blunt one behind. 



The 



