INSECTS. 



otfier hj the longitudinal veflel, and from thofe of the 

 belly by the trachea:. They begin at the union of the firft 

 and fecond rings, by two fafticuli (lightly feparated from 

 each other, wliich are infevted into a kind of tendinous line 

 produced by the union of the fecond with the third ring. 

 The far.ie itrufture exillE in tlic fiibfequent rings. On the 

 third, the fibres of the two fafcicuh, although ftill diftinft, are 

 much more confiderable : on tlie fourth the internal fafci- 

 culus alone has its fibres feparate. The mufcle is continued, 

 without any apparent interfeftion, over all the other rings. 

 It diminiHies in thicknefs towards the oppofite end of the 

 body, and forms again feveral fafciculi ; at firll three, 

 then four, and, lalUy, five or fix. The body is {hortened 

 when thefe mufcles aft in conjuniilion with thofe of the belly : 

 it is curved upwards when they aft alone. 



The longitudinal mufcles of the belly are feparated from 

 each other by the medullary cord, and from thofe of the 

 back by the trachex. Their direftion is precifely the 

 fame with that of the dorfal mufcle. They commence at 

 the Union of the two firft. rings by feveral fafciculi, which 

 are united into one mafs over the third ring. Their fibres 

 are feparated again behind, higher or lower according to 

 the fpecies, and form four or five mufeuhr cords, which ter- 

 minate towards the lad pair of faife feet. Thefe affill the 

 dorfal mufcles in fliortening the body when both fets con- 

 traft together ; but they antagonife them, when they aft 

 feparately, for they then incurvate the body downwards. 



Between the long mufcles of the back and the .Icin 

 ftiorter ones are found, having an oblique direftion. Some 

 are extended from without inwards, towards the dorfal line, 

 between the annular interfeftions. Others occupy the fame 

 interval, but have an oppofite direftion, pafling from within 

 outwards, fo as to defcribe with the former the figure of the 

 letter V. Thefe two orders of oblique mufcles have not 

 every where the fame quantity of fibres. In the firft rings 

 they are narrow and long : thofe of the fourth, fifth, and 

 fixth are much fhorter : further back they become much 

 longer and more numerous in fome fpecies, while in others 

 they ftill continue broad and ihort. Thefe mufcles aft 

 fopardtely on each ring, which they (horten by their fimul- 

 tancous contraftions ; but, as they do not extend over the 

 whole length of the ring, the parts correfpondiag to the 

 folds, over which the oblique mufcles do not pafs, are elon- 

 gated, when, by the aftion of the latter, the diameter of 

 tile ring is diminifiied : thus progrefllon is facilitated. 



Under the long mufcles of the belly is found another 

 ftratiim, of which the fibres are oblique. Tliefe very much 

 refemble the oblique mufcles of the back ; and may be dif- 

 tinguiihed, according to their direftions, into two orders. 

 Thofe of one fet are found nearer to the middle ventral 

 line, iu which the knotted nervous cord is found ; and 

 afcend from within outwards, in the intervals of die rings. 

 Tiic others are not fo oblique, with the exception of the 

 three fiiperior pairs. Thefe mufcles, therefore, form, with 

 the preceding, an angle, fimilar to this kind of ^. 

 'The oblique mufcles which run from within outwardly, 

 or the moll internal, have many fibres. They ufually con- 

 fill of three or four diHinft fafcicuM. Thofe which extend 

 from without inwardly, or the moft external, have fewer 

 fibres, and never more than two fafciculi. 



The aftion of thefe mufcles appears to be fimilar to that 

 of the oblique mufcles of the back ; but it is probable that 

 ({ley alio extend immediately the (kin of the feet on which 

 they are fituatcd. 



Befides the longitudinal and oblique mufcles of the back 

 aiid tlic beliy, caterpillars have fome which are lateral ; 

 that is to fay, mufcles fituated btlow and above the ftigmata 



or apertures, which ought to be defcribed feparately. Thefe 

 mulcles are of three kinds, the Jlraigbt, the tranfverfe, and 

 the oblique. 



The ftraight lateral mufcles are fituated between the annu- 

 lar fcgments, above the ftigmata. They are all placed longi- 

 tudinally one over the other. Their points of attachment 

 are covered by the tranfverfe mufcles. They feem in- 

 tended to bend the body towards the fides when they aft 

 feparately ; but when they contraft, in concert with the 

 long mufcles of the back and abdomen, they fhorten the 

 body, and thereby affift its progreffion. 



The tranfverfe lateral mufcles are of two kinds : fome, 

 which are longer than the others, arife from the intervals un- 

 occupied by the attachments of the ftraight lateral mufcles, 

 and are inferted at the termination of the oblique external 

 mufcles of the abdomen. Their fibres are difpofed fome- 

 what in the form of a fan. The others have the fafciculi 

 formed of parallel fibres ; they are ftiorter, and are extended 

 in each of the rings between the ftraight, lateral, and oblique 

 mufcles of the abdomen. Thefe mufcles diminifii the dia- 

 meter of each ring, and confequently lengthen it in each of 

 its folds. This mode of aftion is iieceifary for progref- 

 fion. 



The oblique lateral mufcles are fitirated on each fide of 

 the ftraight. They proceed in an oblique direftion from 

 below upward, under the infertion of the ftraight lateral 

 mufcles, which they aflift when they aft together. 



Such are the mufcles of the body in general ; but the 

 true and falfe feet, and the head, have particular mufck3> 

 which naift be defcribed feparately. 



The mufcles of the true or fcaly feet are fituated within 

 the three articulations of which thefe feet are formed. They 

 may be diliingniihcd into thofe which move the articulations,, 

 and thofe which aft on the srigiiis, or claw, that terminates 

 them. 



The mufcles of the firft joint con fid of five or fix fafci- 

 culi, which arife from the fuperior margin of this articula- 

 tion, and are inferted into the fuperior margin of the next.. 

 The mufcles of the fecond joint are nearly equal in number, 

 and are inferted into the fuperior margin of the third. 



Tlie mufcles of the unguis terminate by two tendons : 

 but they are formed of feveral fafciculi, fome of which aiife 

 from the fecond and third joints in two very diftinft layers ; 

 others from a hne which correfponds with the convexity of 

 the unguis ; and laftly, others from the hne which anfwers 

 to its concavity. Thefe tendons are inferted into two tuber- 

 cles at the fuperior extremity of the unguis, on the concave 

 fide, towards its point. They ferve to bend the unguis, 

 which probably recovers its pofition by the elafticity of it& 

 articulation. 



There are two mufcles to each of the membranous or 

 falfe feet. Their direftion, with refpeft to the body, ii 

 almoft tranfverfe. They extend from the centre of the feet, 

 into which they are inferted towards the back, and beyond 

 the ftigmata, whence they arife by lateral bands more or lefs 

 oblique. Their ufe is to draw the centre of the foot in- 

 wardly, and to retraft the hooks with which the limb is 

 armed. It is probable that the contraftions of the obhque 

 mufcles of the abdomen produce the oppofite cffeft. 



With refpeft to the mufcles of the head, we ihall at pre- 

 fent defcribe only thofe which produce its entire motion. 

 We (hall notice the others in treating of the different func- 

 tions to which they are fubfervient. The mufcles which 

 aft on the head, bend it upward, downward, and towards the 

 fides. Thofe which bend it upward are very numerous. 

 They arife from the fecond and firft ring, and are inferted 

 into different points of the o>: iput ; fome near the middle 

 7 line,. 



