HOW IS ORGANIC EVOLUTION CAUSED? 405 



lives, all animals undergo perpetual 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 associations ; and many of these 

 acquired forms or properties are transmitted to their pcs- 

 teritv " While it embodies a belief for which a great deal 

 is to be said, this passage involves the assumption that, 

 desires and aversions, existing before experiences of the ac- 

 tions to which they are related, were the originators of the 

 actions, and therefore of the structural modifications caused 

 by them. In his Philosophic Zoologique, Lamarck 



much more specifically asserts " le sentiment interieur," 

 to be in all creatures that have developed nervous sys- 

 tems, 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 1'aide des excitations 

 tju'ils re9oiveut de 1'exterieur." Afterwards he says "je 

 reconnus que la nature, obligee d'abord d'emprunter des 

 milieux environnans la puissance excitatrice des mouvemens 

 vitaux et des actions des animaux imparfaits, sut, en com- 

 posant de plus en plus 1'organisation animale, transporter cette 

 puissance 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." And still more definitely he contends that 

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

 position de 1'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 e*nergiques, 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 



