LETTER XLII. 
INTERNAL ANATOMY AND PHYSIOLOGY 
OF INSECTS, CONCLUDED. 
MOTION. 
WE have seen upon a former occasion the great variety 
of movements that insects can perform, and of the ez- 
ternal organs with which they perform them*: but we 
are now to consider the znternal 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- 
hibit’, we feel no small degree of curiosity to know 
something of that part of their internal structure that 
produces 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. 
2 Vou. IJ. Lerten XXII. Vor. HI. Lerters XXXIV.—XXXVI. 
b Vox. II. p. 283, 299, 310, 314—. &c. 
