220 LAMARCK AND DARWIN 



have no term to express this internal power possessed not 

 only by intelligent animals but also by those that are 

 endowed merely with the faculty of sensation; it is a power 

 which, when set in action by the feeling of a need, causes 

 the individual to act at once, i.e., in the very moment of 

 the sensation it experiences ; and if the individual is of 

 those that arc endowed with intelligence it nevertheless 

 acts in such a case entirely without premeditation and 

 before any mental operation has brought its -icill into 

 play" (p. 24). 



It is the power we call instinct in animals (p. 25), and it 

 implies neither consciousness nor will. It acts by trans- 

 forming external into internal excitations. 



To this second group of animals, possessing the sentiment 

 intcricur, belong the higher Invertebrates, notably insects and 

 molluscs. Only animals possessed of a more or less centralised 

 nervous system can manifest this sentiment, or principle of 

 (unconscious) reaction to external stimuli. 



The higher animals, or the four Vertebrate classes, form 

 the group of " intelligent animals." In virtue of their more 

 complex organisation they possess in addition to the sentiment 

 interienr the faculties of intelligence and will. 



Now, broadly put, Lamarck's theory of evolution is that 

 new organs are formed in direct reaction to needs (<VW//.v) 

 experienced by the sentiment interienr. The sentiment 

 interieitr is therefore the cause not only of instinctive action 

 but also of all morphogenetic processes. Will and intellig- 

 ence (which are confined to a relative!)' small number of 

 animals) have little or nothing to do directly with evolution. 



To understand the working-out of Lamarck's evolution- 

 theory we must revert to his conception of the l-.elielle des 

 ctrcs. What he wrote in the riiilosopliie zoologitjue is here 

 repeated in the work of 1816 with little modification. 



There is a real progression from the simpler to the more 

 complex organisations ; Nature has gradually complicated 

 her creatures by giving them new organs and therefore new 

 faculties. 



It is interesting to note that Lamarck expressly refers to 

 I'xuinet (p. no), but refuses to accept his view of an ILeliellc 

 extcnding down into the inorganic. Like Bonnet, however, 



