INSECTS. 



the tail of which is not covered by articulated fcales, ap- 

 pears to have much fewer ganglia than the cray-iiih. We 

 have obferved only five. 



In the JquiUa, Fabr. there are ten ganglia, without rec- 

 koning the brain : that at the union of the two cords whicli 

 form the collar, tranfmits nerves to the two forceps, and to 

 the three pair of feet which immediately fucceed them, and 

 which in thefe animals are ranged almoft on the fame tranf- 

 verfe line ; this ganglion is therefore the longeil of all. 

 Each of the three following pairs has a particular gnnghon. 

 There are afterwards fi.x ganglia in the length of the tail, 

 which diftribute their ft'amentsto the thick mufcles of that 

 part. The brain produces immediately four trunks on each 

 fide, w'z. the optic, thofc of the two antennx, and the cord 

 which forms the collar. As the antenna: are placed more iaTeral'fiia'me 



1, their nerves are directed back- 



polleriorly than the b 

 ward. 



B. In the Common Crab {Cancer Mums, Linn.) — The 

 brain of the crab refembles that of the cray-fifli in its form 

 and fituation : it alfo furnilTies analogous nerves, but they 

 are direfted more towards the fides, in confequence of the 

 pofition of the eyes and the antennae. The medullary cords 

 which form the collar, detach each a nerve to the mandibles, 

 but the cords are prolonged much farther backward than in 

 the cray-fi(h before they unite. They join only in the middle 

 of the thorax, at which place there is produced a medullary 



mafs of an oval rmg-like figure, which is eicrht times the fize . „ .. „ 



of the brain. The nerves which proceed" to the different "'^'^Y ''"^ beyond the third ring of the body, a great num- 

 parts arife from the circumference of this ring. It fui-niflies ^^"^ of diverging nervous filaments are produced. Thofe 

 fix nerves on each fide to the jaws and the five feet, and there which are ncarelt the head afcend a little ; thofe which fue- 

 ls a fingle nerve which arifes from the pofterior part, and ^eed them proceed almoll 

 proceeds to the tail. This medullary ring may be faid to 



oefophagus, proceeds inferiorly to form the nervous cord 

 fliall prefently defcribe. 



Another pair departs from the inferior furface of 

 brain, or that part which refts upon the oefophagus : t' 

 are firll direfted forward ; they afterwards turn inward, 

 proceed above the middle and fupcrior part of the cefo; :, 

 gus, in order to approach each other. When they come id 

 contaft, they unite and form a fmall ganglion, which pro- 

 duces a fingle nerve ; this nerve, continuing to proceed pel'- 

 teriorly, pafles below the brain, and accompanies the oclu- 

 phagus to the ilomach. It there enlarges again into a 

 ganghon, which furnifhes fome fmall nerves that are fent ti. 

 the ilomach, and one more confiderable, which is continued 

 along ihe inteftinal canal, and fends off, at regular diftanc.s, 

 nts, which arc loft in the coats of this tuLu-, 

 This nerve is analogous to that which Lyonet has dc 

 fcribed under the name of recurrent, in the caterpillar of the 

 cojus. 



The medulla fpinalis, which, as we have fhewn, is formed 

 by the pofterior pair of nerves of the brain, is very thick at 

 its origin : it forms a large fufiform srargUon about 0,005 

 metre long, and half a millimeter broad. Four or five con- 

 tradtions appear on its anterior part, but they are fo (light 

 that they feem only tranlverfe furrows. The pofterior part 

 ot this ganglion is fm.ooth. 



From the lateral parts of this large ganglion, which extend.; 



fverfely ; and the laft 

 diredled more and more pofteriorly : the length of each li 

 in proportion to its diftance from the anterior part of the 

 ganglion. The two moft pofterior filaments are therefore the 

 longett. 



2. Larva of the Stag Beetle {Lucanus Cerz<us).^Ths 

 nerves of this larva differ greatly from thofe of the pre- 

 ceding, although the perfeft infcfts are fo neai-ly allied in 

 genera. 



The brain confifls of two contiguous and almoft fpherical 

 D. In MonocvU- — We know not the nervous fyftem of lobes ; thefe produce four nerves anteriorly for the antenns 

 the molucca crab {llmuhis gigas, Fab. Monociths polyphcmus, and the parietes of the mouth : two inferiorly, which fu-ft 

 Linn.) In the monoculus apus of Linnseus, however, the proceed forward, then turn back, pafs again under the 

 indiftinft nature of that fyftem, joined to fome other pecu- brain, and form a ner\-e known under the name of recurrent. 

 liarities of organization, would almoft induce us to clafs the Laftly, two pofteriorly, which form a collar round the 

 animal with the inarticulated worms. The brain is a fmall oefophagus, and join underneath, to compofe the nervous 

 globule, nearly tranfparent, fituated under the interval of cord of the body. Tliis cord is formed of eight ganglia 



reprefent the ufual knotted cord, but if it has any gangU; 

 they are not vifible. 



C. In the Onifcus AJclhs The two cords which compofe 



the middle part of the nervous fyftem in this animal, do not 

 perfefily join. We can diftinguilh them throughout the 

 whole of their length. There are nine ganglia, exclufive 

 of the brain ; but the two firft and the two laft are fo clofe 

 together, that the number may be reduced to feven 



the eyes. The medullary cord is double, and has an enla 



■ge- 



which extend to the ninth ring of the body. The diftances 



ment at each of the numerous articulations of the body ; between thefe ganglia are very unequal ; they are joined by 



very flender and clofely approximated nervous filaments. 

 The firft ganglion, from the head, is very lai-ge, and almoft 

 fpherical ; it is followed almoft immediately by die fecond, 

 which is one-half lefs, and which is diftiiiguifiied from it 

 only by a kind of contraftion ; the firft produces four pairs 



but the whole is fo thin and tranfparent, that the real nature 

 of the cord can fcarcely be afccrtained. 



Brum and Nerves of the Larva of Infers. 



A. Colcoptera. 



1 . Larva of the Scarahnus Najicornis.—We ftiall give a 

 particular defcription of the nerves of this larva, becaufe 

 their diftribution is eiTentially different from that which takes 

 place in the other coleoptera. 



The brain is fituated under the great fcale which covers 

 the head immediately above the origin of the oefophagus : it 



of nerves on each fide ; one afcends to the head, the other 

 three diverge and are loll in the mufcles of the abdomen, 

 and in thofe that move the head. Tlie fecond ganglion, 

 befides the two nerves tiiat unite it to the third, produces 

 two other nerves, v/hich are alfo directed backward, and loft 

 in the mufcles of the fourth ring. The third ganglion, and 

 _ _ thofe that follow as far as the eighth, are fimilar to the 



confifts of two approximated lobes, which are very diftuid at fecond ; with this difference, tliat they are much more diftant 

 the front and back part. Four nerves arife from the ante- from each other, and that they produce longer filaments, 

 nor part, two on each fide, which are loft in the cirri and in proportion as they are fituated more inferiorly. Laftly, 

 parietes of the mouth. the eighth and ninth ganglia are fo clofe togetlier, that 



From the lateral and fomewhat pofterior parts of the they feem to form but one, with a flight contraftion in the 

 brain, there arifes a pair of nerves, which, embracing the middle. This double ganglion produces three pair; of 



nr-.rves, 



