PHYSIOLOGY OF INSECTS. 95 



argues, then commands ; it takes cognizance of 

 causes, and provides for consequent effects, before 

 the other elements can obey its behests. 



309. The great powers of mind are specu- 

 lation and retention : speculation is the power 

 which supposes an event that has not yet oc- 

 curred ; and retention is the power of preserving 

 an image left on the mind by an event that has 

 occurred. 



310. Of the connexion of mind with the organs 

 which it commands we know nothing ; mind 

 itself is only known by its effects : its commands 

 are carried by the nerves ; a fact ascertained by 

 separating a nerve ; after which separation, the 

 mind no longer controls the parts to which that 

 nerve extended its branches. 



311. The physiology of insects is, however, 

 properly confined to the description of their 

 systems of organs, and to the functions which 

 these organs perform : therefore, excepting as 

 connected with the organs, no farther notice will 

 be taken of any other element than matter. 



312. It must be observed that parts perform- 

 ing obvious offices, are commonly called the 

 organs of those offices ; thus legs are termed 

 organs of locomotion, and jaws, organs of mandu- 

 cation : these terms are not in themselves im- 

 proper, but lead, in some degree, to a vagueness 

 of phraseology. 



313. In the following chapters of this book, 



