LETTER XLIII. 



INTERNAL ANATOMY AND PHYSIOLOGY 

 OF INSECTS, CONCLUDED. 



MOTION. 



\V E have seen upon a former occasion the great variety 

 of movements that insects can perform, and of the ex- 

 ternal organs with which they perform them a : but we 

 are now to consider the internal. apparatus, by the im- 

 mediate action of which they take place their system of 

 muscles. When we reflect upon the wonderful velocity, 

 their size considered, with which many insects move, and 

 the unparalleled degree of muscular force that many ex- 

 ert b , we feel no small degree of curiosity to know some- 

 thing of that part of their internal structure that pro- 

 duces these almost incredible effects. I shall in the 

 present letter endeavour in some degree to gratify that 

 curiosity, and give you an account of the muscles of these 

 little animals, first considering them in general ; and 

 then, as far as my information goes, adverting to those 

 in particular that move the different parts and organs of 

 an insect's body. 



a VOL. II. LETTER XXII. VOL. III. LETTERS XXXIV. XXXVI. 

 * VOL. II. p. 280, 295, 306, 31 0~. &c. 



