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 crayfish. 
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 by 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 the series of molecular changes excited, 
either by internal or by external causes, in its neuro- 
muscular machinery; and, on the other, upon the dispo- 
sition and the properties of the parts 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 difficult to find satisfactory grounds 
