352 ZOOLOGICAL PHILOSOPHY 



which excite it immediately to guide its power of acting in the direction 

 of the acquired propensities. 



It is purely these last kind of causes that constitute instinct ; and 

 seeing that they are not the produce of any deliberation, thought, 

 or judgment, instinctive actions always satisfy surely and unerringly 

 the wants felt and the habits acquired. 



Hence instinct in animals is a compelhng tendency, prompted by 

 sensations in giving rise to needs ; and it causes the execution of 

 actions without the intervention of any thought or act of will. 



This propensity is a part of the organisation acquired by habit ; 

 it is excited by impressions and needs, which move the individual's 

 inner feeling, and cause it to dispatch nervous fluid to the appropriate 

 muscles as required by the propensities. 



I have already said that the habit of using any organ or any part of 

 the body for the satisfaction of constantly recurring needs, gives the 

 subtle fluid so great a readiness for moving towards that organ where 

 it is so often required, that the habit becomes inherent in the nature 

 of the individual. 



Now the needs of animals with a nervous system vary in proportion 

 to their organisation, and are as follows : 



1. The need of taking some sort of food ; 



2. The need for sexual fertiUsation, which is prompted in them by 

 certain sensations ; 



3. The need for avoiding pain ; 



i. The need for seeking pleasure or well-being. 



For the satisfaction of these needs they acquire various kinds of 

 habits, which become transformed in them into so many propensities ; 

 these propensities they cannot resist nor change of their own accord. 

 Hence the origin of their habitual actions and special inchnations, 

 which have received the name of instinct.^ 



This propensity of animals to the preservation of habits, and to the 

 repetition of the resulting actions when once it has been acquired, is 

 propagated to succeeding individuals by reproduction so as to preserve 

 the new type of organisation and arrangement of the parts ; thus the 

 same propensity exists in new individuals, before they have even begun 

 to exert it. 



Hence it is that the same habits and instinct are handed on from 



1 Just as all animals do not possess the faculty of will, so too instinct is not a pro- 

 perty of all existing animals ; for those which have no nervous system have no inner 

 feeling, and cannot therefore have any instinct for their actions. 



These imperfect animals are entirely passive, do nothing of their own accord, feel 

 no needs, and are provided for by nature in everything just as in the case of plants. 

 Now since their parts are irritable, nature causes them to carry out movements, 

 which we call actions. 



