HOW IS ORGANIC EVOLUTION CAUSED! 493 



transformations; which are in part produced by their own 

 exertions, in consequence of their desires and aversions, of 

 their pleasures and their pains, or of irritations, or of associa- 

 tions; and many of these acquired forms or properties are 

 transmitted to their posterity." While it embodies a belief 

 for which much may be said, this passage involves the 

 assumption that desires and aversions, existing before ex- 

 periences of the actions to which they are related, were the 

 originators of the actions, and therefore of the structural 

 modifications caused by them. In his Philosophie 



Zoologique, Lamarck much more specifically asserts " le 

 sentiment interietir/' to be in all creatures that have developed 

 nervous systems, an independent cause of those changes of 

 form which are due to the exercise of organs : distinguishing 

 it from that simple irritability possessed by inferior animals, 

 which cannot produce what we call a desire or emotion; and 

 holding that these last, along with all "qui manquent de 

 systeme nerveux, ne vivent qu'a Faide des excitations qu'ils 

 regoivent de Texterieur." Afterwards he says — " je reconnus 

 que la nature, obligee d'abord d'emprunter des milieux en- 

 vironnans la puissance excitatrice des mouvemens vitaux et 

 des actions des animaux imparfaits, sut, en composant de 

 plus en plus I'organisation animale, transporter cette puis- 

 sance dans Tinterieur meme de ces etres, et qu'a la fin, elle 

 parvint a mettre cette meme puissance a la disposition de 

 rindividu." And still more definitely he contends that if 

 one considers " la progression qui se montre dans la com- 

 position de I'organisation," ..." alors on eut pu aperce- 

 voir comment les besoins, d'abord reduits a nullite, et dont 

 le nombre ensuite s'est accru graduellement, ont amene le 

 penchant aux actions propres a y satisfaire: comment les 

 actions devenues habituelles et energiques, ont occasionne le 

 developpement des organes qui les executent." 



Now though this conception of Lamarck is more precisely 

 stated, and worked out with much greater elaboration and 

 wider knowledge of the facts, it is essentially the same as 



