INSECTS. 



ilarcrc bilobed ganglion, of an irregular quadrangular figure, 

 the fides of which produce feveral filaments for the mufclcs 

 of the anterior feet. 



Tlie jjofterior part of this fecond ganglion furniflies two 

 filaments, which ptiietrate into the bread. The folid ap- 

 pendices of the coxx, which alTbrd iiifertions for the mnfcles, 

 pafs between thefe two filaments. They form a third gan- 

 glion, which correfponds to the middle fpace included be- 

 tween tlie two intermediate feet. This ganglion fends 

 nerves to the mufcles of the wings and the feet. 



The fourth ganglion is alfo contained in the bread. It is 

 fituatcd before and between the pofterior pair of feet. It is 

 produced by two nervous cords from the preceding gan- 

 glion ; and furnifhes two pofteriorly, which are fo clofe to 

 each other, that they appear to the naked eye to make only 

 one cord. This nerve is received and contained in a kind of 

 groove formed above the triangular pifce, which affords an 

 attachment for the mufcles of the feet. 



The other ganglia, which are all fituated in the abdomen, 

 are fix in number. They arc, the laft excepted, of the fame 

 fizi and form, placed at equal diftaiices, and produced by 

 two fimilar and clofely approximated cords. Each fur- 

 nilhes two pair of nerves for the mufcles of the abdominal 

 rings. 



The laft ganglion of the medulla is one-half larger than 

 the fire preceding. It is fituated below the parts of ge- 

 neration, to which it is diltributed by four pair of fila- 

 ments. 



In th: Moh-crtcht {Achtta Gryllo lalpa.) — The brain of 

 this infedl is alfo compofed of two rounded lobes, which are 

 particularly diftinft at the pofterior part. We can clearly 

 perceive the origin of the nerves of the palpi, of the anten- 

 nx, of the fmooth eyes, and of the eyes properly fo called. 

 In general the nerves of the principal medulla are fimilar to 

 thole we have defcribcd in the cock-roach. The two firll 

 ganglia are produced by two nerves. The firft, which is in 

 the corfclet, fupplies the mufcles of the head, bread, and 

 anterior feet. The fecond, which is larger, and in the 

 bread, gives filaments to the mufcles of the wings, and of the 

 intermediate and pofterior feet. It alfo fends two nerves 

 pofteriorly, which produce the abdominal ganglion. The 

 cord then becomes fingle and flat, like a ribband, and con- 

 tains only four ganglia, occurring at differeat diilajices. 

 Each produces two pairs of nerves, which are directed pof- 

 teriorly, and didributed to the mufcles. The firft corre- 

 fponds to the middle part of the firft abdominal ring ; tlie fe- 

 cond to the third, the third to the fifth, acd the laft to the 

 ninth. 



This laft ganglion is the mod remarkable of all. It is of 

 an oval fhape, and produces, from the whole of its circum- 

 ference, nerves which are Jiftributed to the neighbouring 

 parts. Two, which are longer tlian the others, diverge as 

 they proceed backward, and thus reprefent a bifurcation of 

 the medullary cord. Ttiefe branches furnifii filaments to the 

 parts of generation. 



C. Ihm'tpttra — In tin a-ugl Water Scorpion {Nepa Cimma, 

 Linn.) — ^The nervous fyftem of this infect confifts of three 

 ganglia. The firft, wiiich fupplies the place of the brain, is 

 fituated in the head. It is for:red of two approximated lobes. 

 Thefe lobes are pyriform, and touch each other at their bafe. 

 Their fummits are diretted obliquely forward towards the 

 eyes, in which they terminate, and thus anfwcr to the optic 

 nerves by their anterior extremities. The middle and ante- 

 rior part of thefe lobes alfo produce fome filaments for the 

 parts of the mouth. Pofteriorly, the brain detaches two 

 cords, which embrace the cr.fojjhagus as they pafs below it. 

 They unite at the origin of the breall in a tetragonal gan- 



glion : each of the angles of which produces or receives 

 feveral nerves. The anterior rcceiies the two cords which 

 come from the brain ; the pofterior, t!ie two which are the 

 continuation of tlie medullary cord. Each lateral angle pro- 

 duces a fafcic.ilus, compofed of four nerves, which are di- 

 refted to. the ir.ufclcs of the breall and anterior feet. We 

 obferve one of them enter into the cavity of the coxa. 



The two iierves produced by the pollerior angle of the 

 fecond ganglion proceed in a parallel dirtftion backward. 

 Having arrived in the brcaft above the horny appendix, to 

 which the mufcles of the coxx of the intermediate and pof- 

 terior feet are attached, they fwcll into a large round gan-' 

 glion, confiderably more voluminous tlian the brain. A vaft 

 number of nerves arfl detached from the edges of tliis gan- 

 glion, like folar rays. Tlie two mod remarkable filaments 

 are exceedingly long and flender. They extend from the. 

 bread nearly as far as the anus : we have obferved them to 

 terminate by three minute branches i^ the parts of generation 

 of the male, furnilhing, at the fame time, fonic filaments 

 to the adjacent parts. All the other filaments, which pro- 

 ceed from this third and laft ganglion, are dtdincd to'the' 

 mufcles. We can very plainly didinguidi thofe that belong 

 to the middle and interinediale feet, as they are fomewhat 

 larger than the others. 



D. Lep'ukptera — /;; the Zigzag Moth {Phnbr.a Difpar, 

 Linn.) — Thei brain in this fpecies is almod fpheiical. Wa, 

 however, perceive a longitudinal furrow »n the middle line. 

 Its anterior part produces fome exceedingly ller.d^r nerves. 

 There are two large optic nerves on the fides, which pro- 

 ceed into the concavity of the eye. where they terminate by 

 a bulb, winch produces a great number of filaments. 



The oefophagus pafies immediately behind the braki, 

 through a fmall triangular interval, the pofterior fides of 

 which are formed by the two cords of the medulla. Thefe' 

 cords afterwards unite, and proceed in the form of a fingle 

 trunk, on the middle part of which we perceive only a Ion- 

 gitudinal furrow. Arrived in the corfclet, it form.; a gari- 

 glion, the furface of which is reddith. This ganglion pro- 

 duces two nerves pofteriorly, which leave between them an 

 intc-rval that affords a palfage for the horny appendices to 

 w hicli the mufclcs of the coxa; are attached. The two corde 

 again unite behind thefe appendices in the fame cavity of tlie 

 bread, and produce a much larger ganglion, the lateral parts 

 of which furnidi nerves to the mufcles of the wings and 

 feet. It is prolonged pr>fteriorly into a fingle cord, wliich 

 again enlarges when it arrives al,ove the articulation of the 

 breaft with the abdomen into a third ganglion. 



It Ihould be remarked, that this large ganglion, which has 

 the forra of a heart, is the only one, befides the brain, of a 

 completely white colour. All tiie others exhibit darker 

 ftiades, and we obferve in them, when viewed by a glafs, 

 reddifli points more or Icfs elongated and finuous, thatrefem- 

 ble the blood-velfels of iiijeftcd glands. 



The third ganglion is prolonged iiito a fingle cord, whicli 

 produces a fourth ganglion above the firft ring of the abdo- 

 men. The latter, as well as thofe that fucceed it, detach on 

 each fide a long flender nerve which paff'S under the mufcu- 

 lar fibres, i)recifely in the fame manner aa the threads of the 

 woof pafs through the warp in cloth. Their direftiun is 

 completely tranfverfe. The fifth ganglion does not differ 

 from the preceding. It is prolonged into a fiiglc cord, upcm 

 which we can ftill very dillinAly perceive the longitudinal 

 furrow. It is fituatcd in the middle part of the third ring 

 of the abdomen. The lixth ganglion is, in every refpcct, 

 fimilar to the preceding ; it is placed in the middle of the 

 fourth ring. Fitially, the feventh and laft ganglion is much 

 larger liian tholt that precede it in die abdomen. It is of an 

 ■Y Z oval 



