INTERNAL ANATOMY OF INSECTS. B73 
Chabrier seems to think that, in some cases, the back 
that intervenes between each pair of wings is the medium 
by which the muscles act upon it?. 
vi. Motions. Irritability is the universal distinction of 
the muscular fibre,—when put in action by the will or 
involuntarily, it causes it to contract or become shorter ; 
and the intermediate agents of the will and other causes 
are the nerves, which, as galvanic experiments seem in 
some degree to prove, are the conductors of an invisible 
fluid or power which immediately causes that action. If 
a nerve is divided, the muscles to which. it renders obey 
it no longer, evidently proving that the nerves cause mus- 
cular irritability®. How this contraction is immediately 
effected, —whether the fibre, as some suppose, undergoes 
any crispation, or becomes zigzag° ; or whether there is 
any sudden change in their chemical composition that ra- 
pidly and strongly augments their cohesion, as Cuvier 
hints¢?, cannot be clearly ascertained, unless a Bauer 
could submit the diving fibre to his glasses. All that we 
know certainly on the subject is, that muscles alternately 
contract and relax at the bidding of the will or involun- 
tarily, and so occasion all the movements of animal bo- 
dies. 
II. Having considered the muscles of insects in gene- 
ral, I must next make a few observations, as far as my 
means of information will enable me, upon those that 
move their different parts and o7,gans—at least the princi- 
pal ones; since to descend to minutiae would be an end- 
less and unprofitable labour. As larve, except those 
> Toviie. ® Cuv. Anat. Comp. i. 94—. 
© N. Diet.id’ Hist. Nat. xx. 80. “" Ubi supr. 101—. 
