LAMARCK: SENTIMENT INTERIEUR 223 



In the large group of apathetic or insensitive animals, 

 which do not possess this faculty, needs cannot be experi- 

 enced ; accordingly new organs are here formed directly and 

 mechanically, by the movements of the vital fluids set in 

 action by excitations from without the evolution, like the 

 behaviour, of these animals is due to the direct and physical 

 action of the environment. " But this is not the case with 

 the more highly organised animals which possess feeling. 

 They experience needs, and each need felt, acting upon their 

 ' inner feeling,' immediately directs the fluids and the forces 

 to the part of the body where action can satisfy the need. 

 Now, if there exists at this point an organ capable of per- 

 forming the required action, it is quickly stimulated to act; 

 and if the organ does not exist and the need is pressing 

 and sustained, bit by bit the organ is produced and developed 

 in proportion to the continuity and the energy of its use " 



(P- 155). 



In intelligent animals the sentiment interieur may be 



moved by thought or will. 



As an example of the way in which the law works 

 Lamarck takes the hypothetical case of a gastropod mollusc, 

 which as it creeps along experiences dimly the need to feel 

 the objects in front of it. It makes an effort (unconscious, 

 be it noted) to touch these objects with the anterior portions 

 of its head, and sends forward continually to these parts 

 a great volume of nervous and other fluids. From these 

 efforts and the repeated afflux of fluids there must result 

 a development of the nerves supplying these parts. And as, 

 along with the nervous fluids, nutritive juices constantly flow 

 to the parts, there must result the formation of two or four 

 tentacles in the .places to which these fluids are directed. 

 A curious mixture of mechanistic " explanations " and 

 vitalistic hypothesis ! 



In his third law, that use and disuse are powerful to 

 modify organs, Lamarck is upon more solid ground, and can 

 point to many instances of the visible effect of these factors 

 of change. It is of course rather closely bound up with his 

 second law and may even be regarded as an extension 

 of it. 



The law has reference to one of the most powerful means 



