344 ZOOLOGICAL PHILOSOPHY 



for the production of such movements ; and nervous influence is no 

 less adequate for exciting that activity. Now I recognised that in 

 animals, which possess physical sensibility, the emotions of the inner 

 feeling constitute the power which drives the exciting fluid to the 

 muscles, and the problem thus seemed to be solved as far as these 

 animals are concerned ; in the case of animals so imperfect as to 

 possess no physical sensibility, stimuli arriving from without are 

 obviously sufficient for their movements, for they are just as irritable 

 or even more irritable in their parts than the others. 



In my opinion, this clears up a mystery which seemed indeed difiicult 

 to penetrate ; nor does this solution seem to me to rest on mere 

 hypothesis : for in the case of sensitive animals, muscular power and 

 the need for nervous influence to excite that power are not hypo- 

 thetical ; and the emotions of the inner feeling, which I regarded as 

 being capable of driving to the muscles the fluid that excites their 

 activity, appeared to me too manifest to be regarded as conjectural. 



If now we closely consider all existing animals, including the state 

 of their organisation, the consistency of their parts, and the various 

 circumstances under which they live, it will be difiicult not to admit 

 that the most imperfect of them, which have no nervous system and 

 hence no muscular activity to help their movements and actions, 

 move by a force that is outside them, that is to say, one which they do 

 not possess themselves and is not available at will. 



It is true that it is in the interior of these delicate bodies that the 

 subtle fluids, entering from without, set up the agitations witnessed in 

 their parts ; nevertheless it is impossible for these fragile creatures, 

 on account of their weak coherence and extreme softness, to contain 

 within themselves any power capable of producing their movements. 

 It is only as a result of their organisation that these imperfect animals 

 act in a methodical manner, which they could in no wise originate for 

 themselves. 



Now, nature has wrought her various productions by slow and gradual 

 stages ; she has created the various organs of animals in turn, varying 

 the shape and situation of these organs according to circumstances 

 and progressively improving their faculties. Hence we feel that she 

 must have begun by borrowing from without, that is, from the environ- 

 ment, the force which produces the organic movements and those of 

 the external parts ; that she afterwards transferred that force within 

 the animal itself, and that finally, in the most perfect animals, she made 

 a great part of that internal force available to their will, as I shall 

 shortly show. 



If we do not carefully note the gradual order followed by nature 

 in the creation of the various animal faculties, I believe that we shall 



