INSECTS. 



All thefe genera liave palpi of a fingle piece. The tipulx 

 and culices have them articulated, and often very long ; the 

 trunk of the tipulse is (liort, with large lips, and no bridle; 

 that of the culices is long, flender, and contains a fine 

 bridle. 



In the oellri, all the external oi'gans of the mouth are •with- 

 drawn within the head, fo as to expofe externally only three 

 rather prominent points. 



The hemiptera (rhyngota, Fabr.) are more uniform in the 

 ilaifture of thefe parts than the diptera ; in general they have 

 a tube compofed of fome articulated pieces, and open above 

 in its whole length. This tube contains three fine bridles 

 nearly as long as itfelf; it exhibits fcarcely any other va- 

 rieties except in its pofition and inflexions. 



The lepidoptera (gloffata, Fabr.) are equally uniform in 

 the ftruclure of thefe parts : their tongue is formed of two 

 membranous plates, curved tranfverfely in their whole length, 

 fo as to form a tube, and, when the infeft does not employ 

 it, convoluted fpirally, and lodged between two flat villous 

 palpi, compofed commonly of three pieces. The differences 

 depend on the variable length of this organ, which is fome- 

 times very inconliderable, and on the figure of the palpi : 

 they are not of importance in connedliou with our prefent 

 fubjea. 



Among the aptera, the loufe has only a fimple and (liort 

 fucker, inclofed in a fmall prominence : the flea has one with 

 two bridles, inclofed in a (heath of three pieces, opened 

 longitudinaUy above. 



Intejiinal CaAal. — It is ftraight in the cruftacea, and uniform 

 in its fize, with the exception of the ftomach. The latter 

 is very different in the crudacea decapoda, and in the branchi- 

 opoda , it pofieffes, in the former, a Angularity of drufture, 

 which is remarkable as the only example of the kind in the 

 whole animal kingdom ; that is, it is fupported by a bony 

 apparatus, a fpecies of flceleton, and confequently does not 

 collapfe when empty. The deftination of this apparatus is 

 rot lefs extraordinary than its exiftence ; it ferves to fupport 

 five hard and moveable teeth, which perform in the cavity 

 of the domach a true raallication. They are placed before 

 the pylorus, and allow no fubftances to pafs through that 

 opening until they are perfeftly triturated. 



The ftomach is found in the thorax above the mouth, and 

 the oeiophagus communicates with it by a large aperture. 

 The anterior portion is more capacious than the polterior, 

 and the teeth are placed where the cavity begins to grow 

 narrower. On the fuperior furtace, or that which is op- 

 pofed to the mouth, there is a thin tranfverfe plate occupy- 

 ing the middle of the domach. This fupports the firft tooth 

 or bony oblong plate, confolidatcd to the fuperior furface of 

 the ftomach, direfted towards the pylorus, and terminating 

 behind in a tubercle. 



On this pofterior extremity is articulated a fecond plate, 

 direfted backwards, bifurcated like the letter Y ; and on 

 each of its lateral divifions another is articulated, which turns 

 forwards and outwards, and reaches the lateral extremity of 

 the firft tranfverfe plate. The two largeft teeth are fixed 

 on thefe two lateral pieces. They are oblong, have flat 

 crowns, which are grooved tranfverfely, and the grooves 

 and inequalities vary in the different fpecies. In the 

 cancer pagurus of Linnseus, the crown is finely ftriated, has 

 large denticuli at its lower edge, and a prominent part 

 in iront which is not ftriated. In the lobfter there are nine 

 tranfverfe ribs, of which the three front are much the 

 largeft. 



From the poiat of union of the tranfverfe portion with 

 the lateral of each fide, another lateral piece is continued, 

 proceeding lower than the firft, and having at its extremity 



a lateral tooth fmaller than the preceding, placed rnfher bfi 

 fore and below its anterior extremity, and having three aixi 

 fometimes even five fmall, (harp, and bent p'oints. The two 

 fm-.ill teeth with curved points fei/.e the nouriftiment which 

 comes from the mouth ; they convey it between the two 

 teeth with flat crowns, which bruife it between each other 

 and again ft the firft fingle plate. 



When it has undergone this operation, the aliment paffes 

 through the narrow part of the ftomach, where its courfe 

 is ftill interrupted, firft by a fleftiy oval prominence cor- 

 refponding to the interval of the two large lateral teeth, 

 and afterwards by a (liarp crida, which divides the pylorus 

 into two half canals. 



There are mufcular fibres in this ftomach, which approxi- 

 mate the bony pieces, and the teeth which they fuppcrt : 

 there are exterior mufcles which feparate the teeth from 

 each other, and are attached to the neighbouring, and par- 

 ticularly the lower parts of the thorax. Thefe mufcles 

 muft be fubjeft to the will, which is another remarkable fin- 

 gularity belonging to thefe ftomachs. 



Thefe teeth are difcharged from the ftomach when the 

 old ftiell is died ; and are fupplied by new ones. 



After this large ftomach, which is always dilated, comes 

 a very flender inteftine, which takes a ftraight courfe to its 

 termination at the end of the tail. Towards its middle a 

 thick ling is obferved, on the infide of which there is a 

 ttrong valve, and the commencement of a very long ca:cum. 



Thefe circumifances have been afcertained in thofe cancers 

 which have long tails, as the cray-fifli and the lobfter, alfo 

 in the paraiitical fpecies (the hermit crab), and in the crabs, 

 as the cancer pagurus, puber, and maenas : the ftrufture may 

 therefore be confidered as common to all the cruftacea deca- 

 poda. The branchiopoda poffefs a fmall membranous fto- 

 mach, fliaped Uke a triangular prifm, furnidied on each fide of 

 its pofterior extremity with a row of fmall pointed teeth, 

 and followed by a very tliin inteftinal canal, continued firom 

 one end of the body to the oilier, and nearly uniform in 

 fize throughout. 



In the onifci the front of the canal is a httle fwollen com- 

 pared to the continuation. 



In the reft of the clafs of infefts w-e find as many varieties 

 in the ftrudlure of the alimentary canal, as in all the clafles 

 of vertebral animals together. There are not only dif- 

 ferences between the families and fpecies, but often very 

 confiderable ones between the larva and perfect dates of the 

 fame infeft : and all thefe varieties bear a very accurate rela- 

 tion, which in many cafes can be very clearly appreciated fo 

 theanim.al's kind of life, whether of fliorter or longer dura- 

 tion. Thus the voracious larva» of the fearabxi and buUer- 

 flies have inteftines ten times as large as the winged and fober 

 infefts, if we may be allowed to ufe that term, to which 

 they give birth. 



There are the fame general refemblances in the natural 

 families of infefis, as in the reft of the animal kingdom ; 

 thus all the coleoptera lamelhcornia, all the carnivora have 

 fimilar inteftines in each of their ftates, &c. Here, as in 

 the other claffes, the length and complication of the intef- 

 tinal canal indicate a vegetable nourilliment ; fiiortnefs and 

 thinnefs, on the contrary, ftiew that the animal is carnivo- 

 rous, &c. 



I. In the Coleoptera. — We fhall felefl for defcription fome 

 very natural families, which are remarkable for any pecu- 

 liarities of dnidlure, and ftiall notice togetlier the intef- 

 tinal canal of the larva and of the perfctl infeift, in order to 

 exhibit in the cleared view^ the very ftrikiiig difference I c- 

 tween thefe two ftates. 



I. In the coleoptera lamcllicornia. The laft mcnt; 



3 1 - 



