INSECTS. 



nerves, which are mucli elongated, and extend to the parts 

 near the amis. 



3. Z.iiri\t of the Cerainbyx, Hydropbilus, Carabus, and 

 Staphyllnvs. — ^l''he nerves of thefe larvae being very fimilar, 

 it will be fufficient to dcfcribe tliem in one genus only. We 

 ihall take for our example the larva of the great diver 

 (HydrophUus pkeus). 



The brain in this animal is fituatcd in the head, above the 

 origin of the oefophagus; it is formed of two lobes which 

 lie ver)' clofe together. Vrom its anterior part it detachts 

 fome filaments to the palpi, the antenna:, and the parietes of 

 the raeuth. Its lateral parts produce two cords which fur- 

 round the ctfophagus, and which are the origin of the ner- 

 vous cord fituated infenorly. It is probable that recurrent 

 nerves alfo arife from this inferior part, but we have not yet 

 been able to difcover tiiem. The chief nervous cord is 

 compofed of ten ganglia, each of which produce three pairs 

 of nerves that are loll in the mufcles of the abdomen, and 

 without any dillinft appearance of their being diftributed 

 to the intePiines. This induces us to believe that there is 

 a recurrent nerve. The firft ganghon is very large ; it is 

 prolonged pofteriorly into two nervous filaments, confider- 

 ably removed from each other ; the fecond is almoft fimilar, 

 but the third is very near the fourth, which produces only 

 a fingle filament pofleriorly. All the others, as far as the 

 tenth, prefent no peculiarity. The hit is divided by a 

 feniible contradion ; from the firft portion a fingle filament 

 arifes on each fide, and from the fecond, three pairs of nerves 

 are detached: thus four pairs of nerves arife from this 

 ganglion. The fourth pair is direfted to the rudiments of 

 the parts of generation, which are very dillinft in thefe larvae 

 in the lafl period of their growth. 



4. Larva of the Water Beetle {Dyttfcus Margina/u) 



The brain of this larva is fpherical, and confills of a fingle 

 lobe, fituated in the head above the origin of the oefophagus ; 

 its anterior part produces fome filaments for the mouth ; and 

 its lateral parts the two optic nerves ; the latter are com- 

 pofed of two parts which are very dilliiift as to form. The 

 firll portion, or that which is next the brain, is of an oval 

 figure, pointed at the extremity which joins the brain ; the 

 other extremity is rounded, and produces a flender nerve, 

 which goes directly to the eye. It is nearly of the fame 

 thicknefs throughout the whole of its extent ; but it is 

 enlarged at its tree extremity into a bulb, from which the 

 nervous filaments of the eye arife. 



The two cords which embrace the oefophagus are (hort 

 and thick •, they arife from the inferior furface of the brain, 

 and immediately unite below the oefophagus, in a large 

 fquare-fliaped ganglion, which produces anteriorly the nerves 

 of the mandibles, and polteriorly two cords, which pafs 

 from the head into the corfelet. There is a greater distance 

 between this firft ganglion of the nervous medulla and the 

 fecond, than between any of the others. It is more than dou- 

 ble that v/hich exills between the two next ganglia. The 

 fecond ganghon is round ; it produces two pair of nerves la- 

 terally ; the anterior for the mufcles which ?.&. upon the 

 head, the poftericr for thofe which move tt;e anterior feet. 

 There are two cords pofteriorly, which are directed into 

 the breaft. The third ganglion is fimil.ir ip every refpecl to 

 the fecond ; it furnifties nerves to the intermediate pair of feet. 

 The fourth ganglion is alfo produced by the two cords which 

 come from the preceding; it is fituated on the union of the 

 abdomen with the breaft ; it is more broad than long. 

 I..aterally it produces two pair of nerves, which run tranf- 

 ▼rrfely parallel, and are loft in the mufcles. The other 

 eight ganglia are placed clofe behind each other, and the 

 fpace between them U fo fmall, that we caii fctircely perceive 



the two nervous filaments which unite them ; they alfo de- 

 creafe in thicknefs, without diminilhing in breadth, as they 

 extend pofteriorly. They all furnifti laterally a pair of very 

 long nerves, which float in the abdomen, and for the moft 

 part terminate in the mufcles that move the wings. One 

 pair, however, proceeds to the rudiments of the parts of 

 generation. 



B. Orthoptera and Hemtptera. — The nerves of the larva: 

 of orthoptera and hemiptera prefent no fenfible difference 

 from thoie we obferve in the perfed infers. It will be fuf- 

 fii.i nt, therefore, to defcribe the nerves of the latter. 



C. Hymetioplera. ~lr\ the larva of tlie faw-fly {Tenthredo, 

 Linn.), which hasa large head furnilhed with eyes, the brain 

 is very broad and fhort ; it feems to form four bulbs of 

 equal magnitude, and nearly fpherical j the two external 

 ferve as the bafe of the optic nerves, which are flender, and 

 which enlarge a little at their other extremity. The firft 

 ganglion is produced by two very fmall nerves, which arife 

 from the inferior furface of the brain, and which, after 

 having embraced the oefophagus, unite under the firil 

 ring of the body ; it furnifhes filaments to the mufcles of 

 tlie feet, and terminates pofteriorly in two other nerves, 

 which, at the dillance of one line, produce a fecond 

 ganglion, and fo on in fucceflion ; the nervous cord is in 

 tills manner formed of eleven ganglia, without reckoning 

 the brain ; the farther the ganglia are removed from the 

 head, the more they diminifh in thicknefs ; they are all nearly 

 of a round form. 



D. Neuroptiva. — In the larva of the lion-ant (ATyrmehcr. 

 formicarius), the nervous fyftem has fome relation to that of 



tlie larva of the dipterous infefts which we fhall afterwards 

 defcribe. 



There is a brain fituated in the head ; it produces nerves 

 analogous to thofe we have already pointed out in the other 

 larvae. The nervous medulla confifts, in the firft place, of 

 two ganglia, which are compofed of two lobes, fituated 

 clofe together ; thefe two firft ganglia are feparate 

 from the others, and contained in the part correspond- 

 ing to the feet, or in the thorax. The remainder of 

 the nervous medulla is enclofed in the abdomen ; it 

 confifts of eight ganglia, placed in an exceedingly clofe 

 feries, and each formed of two lobes ; the firft is nearly 

 double the fize of the other feven. This fuccefTion of 

 ganglia appears to the eye like the extremity of the 

 tail of a rattle-fnaJce ; the laft is round ; the others are 

 more broad than long. All thefe gangha furnifh nerves to 

 the mufcles. It is probable that this difpofition and approxi- 

 mation of the ganglia have a relation to the changes which 

 take place in the infeft at the moment of its metamorphofis, 

 as its abiii^men then occupies fix times the fpace it does in 

 the larva ilatc. 



In thoie larvs of neuroptera, which are nearly as long as 

 the perfect infedl, we find that the ganglia are feparated in 

 the ufual manner. 



The larva of the ephemera has eleven ganglia, without " 

 including the brain, which furnifhes two large optic nerves. 

 There are three ganglia in the thorax, and feven in the ab- 

 domen : the firft fix, reckoning all the ganglia, furnifh more 

 nerves than the five laft. 



The larvx of the dragon-flies have a fmall two-lobed 

 brain, which produces optic nerves, larger or fmallcr ac- 

 cording to the fpecies. The genus aefhna has them the 

 largeft. The reft of the nervous fyftem forms a feries of ■ 

 ganglia of different fizes. In the acflma, the corfelet con- 

 tains Cix, the two laft of which are the largeft of all. 

 There are feven fmall and equal ganglia in the abdomen. 



E. Lipidoptcra. — The nervous fyftem of caterpillars con- 

 fills 



