HOW IS ORGANIC EVOLUTION CAUSED? 493 



transformations; which arc 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.&quot; 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, wore the 

 originators of the actions, and therefore of the structural 

 modifications caused by them. In his Philosophic, 



Zooloyique, Lamarck much more specifically asserts &quot; le 

 sentiment intericur&quot; 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 &quot; qui manquent de 

 systeme nerveux, ne vivent qu a 1 aide des excitations qu ils 

 regoivent de 1 extericur.&quot; Afterwards he says &quot; je reconnus 

 quo la nature, obligee d abord d emprunter des milieux en- 

 vironnans la puissance cxcitatrice des mouvemens vitaux et 

 des actions des animaux imparfaits, sut, en composaiit de 

 plus en plus 1 organisation animale, transporter cette puis 

 sance dans 1 interieur meme de ces etres, et qu a la fin, elle 

 parvint a mettre cette meme puissance a la disposition de 

 1 individu.&quot; And still more definitely he contends that if 

 one considers &quot; la progression qui se montre dans la com 

 position de 1 organisation,&quot; ...&quot; 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 satisf aire : comment les 

 actions devenues habituelles et energiqucs, ont occasionne le 

 developpement des organes qui les cxecutcnt.&quot; 



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 



