180 INTERNAL ANATOMY OF INSECTS. 



Chabrier seems to think that, in some cases, the lack 

 that intervenes between each pair of wings is the me- 

 dium by which the muscles act upon it a . 



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 

 muscular irritability 5 . How this contraction is imme- 

 diately effected, whether the fibre, as some suppose, 

 undergoes any crispation, or becomes zigzag c , or whe- 

 ther there is any sudden change in their chemical compo- 

 sition that rapidly and strongly augments their cohesion, 

 as Cuvier hints d , cannot be clearly ascertained, unless 

 a Bauer could submit the living 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 involuntarily, and so occasion all the movements of 

 animal bodies. 



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 organs at least the prin- 

 cipal ones ; since to descend to minutiae would be an 



a PLATE XXII. FIG. 11,12. c. Chabrier Sur le Voltes Ins. c. iii. 

 t. xi. viii./. 9. S. D. a, k. c. i. 440 -. b Cuv. Anat. Comp. i. 94. 

 c N. Diet. d'Hist. Nat. xxii. 80. " Ubi supr. 101 . 



