GENERAL PRINCIPLES 53 



it is not true that animals are sensitive creatures endowed without 

 exception with the power of producing acts of will, and consequently 

 with the faculty of voluntary locomotion. Hence the definition 

 of animals hitherto given to distinguish them from plants is altogether 

 unsuitable ; in consequence, I have already proposed to substitute 

 the following as more in harmony with the facts, and more suitable 

 to characterise the beings which compose the two kingdoms of living 

 bodies. 



Definition of Animals. 



Animals are organised living bodies, which have irritable parts 

 at all times of their lives ; which nearly all digest the food on which 

 they live ; and which move, some by acts of will, either free or 

 dependent, and others by stimulated irritability. 



Definition of Plants. 



Plants are organised living bodies whose parts are never irrit- 

 able, which do not digest or move either by will or true irritability. 



We see from these definitions, which are much sounder and more 

 accurate than those hitherto received, that animals are primarily 

 distinguished from plants by the irritability which all or some of 

 their parts possess, and by the movements that they can produce 

 in these parts, or which are set up by external causes as a sequence 

 of their irritability. 



It would doubtless be wrong to agree to these new ideas merely 

 on authority ; but I think that every unprejudiced reader who takes 

 into consideration the facts and observations which I shall set forth 

 in the course of the present work will be unable to deny them pre- 

 ference over the ancient ones for which I am substituting them ; 

 since the latter are obviously contrary to all observation. 



We shall terminate this general outlook upon animals by two some- 

 what curious considerations : one concerning the extreme multiphcity 

 of animals on the surface of the earth and in the waters, the other 

 concerning the means adopted by nature to ensure that their number 

 shall never become injurious to the preservation of her productions 

 and of the general order which should exist. 



Of the two kingdoms of living bodies that comprising the animals 

 appears much richer and more varied than the other : at the same 

 time it exhibits more wonderful phenomena in its organisation. 



The surface of the earth, the waters, and to some extent even the air 

 are populated by an infinite multitude of diverse animals, the races 

 of which are so varied and numerous that a large proportion of them 



