INSECTS. 



body, in tlie fame manner as the long mufclcs of the back 

 and belly. 



The mufcles of the feet are the fame as in the porfei^ 

 hifea. ^ 



The head has no particjlar mufcles. The long mufcles of 

 the back, being inferted into the occiput, become exten- 

 fors. The firll tranfverfe lateral pair are inferted beneath 

 the head, and produce the lateral flexion. The long oblique 

 mufcles, which tcrininate at the inferior part of the head, 

 become real flexors. 



4. Mufcles of the Larva of a Ceramlyx. — In the larva? of 

 the cerambiccs we find the fame mufcles as in thofe of the 

 fcarab-.ci ; bu;. as the fliape of the body differs confiderably 

 in thefe two kinds of larvx, there rcfults fome variation in 

 the form and extent of the mufcular organs. 



A great part of the head of the larva of the cerambices 

 ran be drawn within the fliin whenever the animal pleafes. 

 Very (Irong mufcles, fimilar to thofe we have defcribed in 

 the fcarabsEus, are appropriated to this function. As the 

 head, which is very large, enters into the body, the extre- 

 mity which reeeiv-es it is fomewhat thicker than the fame part 

 of the fcarabii, and the mufcles which move the rings are 

 more extcnfive than iheirs. 



The flat flefhy tubercles which we find continued along 

 the back and belly, are a kind of feet, which this larva ufes 

 in progreffion. They move by the alternate contradions 

 of the coritfpondent mufcles : this larva, therefore, moves 

 with equal facility on the back and on the bcUv. 



Of the Organs of Motion In Perfra Itftfis—TlK great 

 variety of motions which infers are capable of performing, 

 entitles them to hold the firll rank among the animals that 

 have no vertebne. We difcover, in thefe minute beings, all 

 the requifites necefTary to produce thofe voluntary actions, 

 the execution of which allonilhes us in vertebral animals of 

 far greater magnitude. They even unite feveral functions 

 which are very feldoin found combined in the other claifes ; 

 for infe£ts walk, run, leap, fwim, and fly with as much fa- 

 cility as the mammalia, birds, and fiflies exercife one or more 

 cf thefe faculties. 



Infedts are probably indebted for this advantage to the 

 numerous articulations of which their bodies are formed. 

 We mull therefore pay attention to their different articula- 

 tions, before we proceed to examine the actions they permit 

 or produce. 



I. Of the Head. —Tor a (lefcription of the manner in 

 which the head is articulated to the thorax, fee Entomo- 

 lOGV, under the divifion Caput, or Head. 



The mufcles which move the head are fituatcd within the 

 thorax. We Hiall defcribe here only thofe moll generally 

 met with. The levators or extenfors of the licad are com- 

 monly fituatfcd in the fuperior part of the corfelet, and the 

 deprcffors inferiorly. 



Immediately beneath the middle dorfal part of the corfelet, 

 we find a pair of mufclcj which arife from the anterior portion 

 of the fcutellum, when that part cxills ; or from the fupe- 

 rior part of the peilus. Thefe mufcles are inferted into the 

 pottcrior and fuperior part of the head, on the edge of the 

 occipital hole : they draw the head back, and lift it up when 

 ii is dtfpreffed. 



On the lateral parts of this firll pair we find another which 

 is more flender : the infertion of this pair likewife takes 

 place at the occipital hole, but more outwardly. They 

 arife obliquely from the lateral parts of the corfelet. Thofe 

 mufcles turn the head to one fide when they a£l feparately ; 

 th.'y raife it, and bring the mouth into the middle line when 

 fhcjr contrad togeti. r. It will be ealily conceived that 

 4 



infefts which hate tlie head articulated like a knee, thef-- 

 rotatory mufcles are much ftronger and more confpi. 

 cuous. 



The flexors of the head are alfo four in number, two on 

 each fide. The firft pair arifes in the internal inferior part 

 of the pectus, from a fmall horny procefs, which, in the 

 colcoptera is of a fquare form, and haj the four angles ter- 

 minated by folid branches. Thefe mufcles extend diredly 

 to the inferior part of tlic occipital hole. From their po- 

 fition they doubtlefs move the head diredtly backward. The 

 fccond pair, which are much fliorter, arife from the inferior 

 lateral part of the corfelet, and proceed to the fide of the 

 preceding, with which they concur in their effeft when they 

 act together ; but when one of the tv.'o contracts feparately 

 it bends the head to the fide. 



2. For the defcription of the t/iorax or corfelet, cf the 

 piStij or breall, and of the abdomen or belly, fee ExTO- 

 iiOLOC.y, under the refpeftive divifions. 



:;. Of the Members. — For an account of the number and 

 flrufture of the feet, fee Estomolocy imder the divificm 

 Members. 



The motion of each joint'is performed in a fingle place. It 

 is provided with two mufcles only, which are enveloped in the 

 preceding joint. They are an extenfor and a flexor. 



In the colcoptera the coxse move by a kind of rotation oh 

 their longitudinal axis, which is fituated tranfverfely, and 

 forms, with the middle line of the body, an angle more cr lef» 

 approaching 90". As the femur is attached to the internal 

 extremity of the coxa, the diftance between the thighs is 

 greateft; in thofe infefts in which the femur is moil b'.nt with 

 re fp eft to the coxa, to which it is articulated. It is obvi- 

 ous, therefore, that the pofition of the plane in which this 

 flexion is made, depends upon the fituation of the coxa ; 

 when it is turned forward, the plane is vertical ; when turned 

 backward the plane is always more oblique ; and in tlie in- 

 fcCts that fwim, it is even horizontal. It appears, then, that 

 the almoil imperceptible motion of the coxa determiiies the 

 moll remarkable movements of the feet. 



The mufcles of each pair of cox<e and femora are fituated 

 in the fuperior of the corfelet or of the pefius. To obtain 

 a proper view of them, it is necefTary to cut the body of the 

 infed in a vertical dircftion. Over the lall pair in the 

 pe£tus there is a fcaly fubilance, in the form of a Y. The 

 fl;alk of this part affords an origin to a mufcle which turns 

 the coxa backward, and is inferted in'o its pollerior 

 edge. The mufcle which turns it forward arifes from the 

 back, and is inferted by a thin tendon, into its anterior 

 edge. 



The mufcle which extends one femur, while it is approxi- 

 mated towards the other, is very confiderable. It ariles from 

 the whole branch of the piece in the form of a Y, and is 

 inferted into the internal edge of the head of the femur. Its 

 antas^onill is fituated within the body of the coxa. 



The mufcles which extend the two pairs of anterior femo- 

 ra, arife from the correfponding dorfal parts, and not from 

 particular internal fubftances : the flexors, however, are al- 

 ways fituated within the body of the coxs. 



The mufcles which turn the coxse arife alfo from the pa- 

 rietes of the corfelet ; viz. the mufcle which moves it back- 

 ward, from the dorfal part, and that which moves it for- 

 ward, from the lateral part. In the w.iter beetles, which, 

 as we have obferved, have the pollerior coxa confolidated and 

 immoveable, thefe mufcles feem to extend to the femur, 

 which is therefore furniflied with four, two extenfors and 

 two flexors. 



The 



