THE MORTALITY OF CRAYFISHES. 127 



ning of this chapter, so far as such obscure consciousness 

 accompanies the molecular changes of its nervous sub- 

 stance, it will be right to speak of the mind of a craj'fish. 

 But it will be obvious that it is merely putting the cart 

 before the horse, to speak of such a mind as a factor 

 in the work done bj^ the organism, when it is merely a 

 dim symbol of a part of such work in the doing. 



Whether the crayfish possesses consciousness or not, 

 however, does not affect the question of its being an 

 engine, the actions of which at any moment depend, on 

 the one hand, upon Ihe series of molecular changes excited, 

 either by intei'ual or by external causes, in its neuro- 

 muscular machinery ; and, on the other, upon the dispo- 

 sition and the proj)erties of the j^arts of that machinery. 

 And such a self-adjusting machine, containing the im- 

 mediate conditions of its action within itself, is what is 

 properly understood by an automaton. 



Crayfishes, as we have seen, may attain a considerable 

 age ; and there is no means of knowing how long they 

 might live, if protected from the innumerable destructive 

 influences to which they are at all ages liable. 



It is a widely received notion that the energies of living 

 matter have a natural tendency to decline, and finally 

 disappear ; and that the death of the body, as a whole, 

 is the necessary correlate of its life. That all living 

 things sooner or later perish needs no demonstration, 

 but it would be diflicult to find satisfactory grounds 



