28o LAMARCK, HIS LIFE AND WOKIC 



zation perfects itself and becomes gradually compli- 

 cated in a most remarkable way?" 



This leads him to consider what is life, and he re- 

 marks (p. XV.) that it does not exist without external 

 stimuli. The conditions necessary for the existence 

 of life are found completely developed in the simplest 

 organization. We are then led to inquire how this 

 organization, by reason of certain changes, can give 

 rise to other organisms less simple, and finally origi- 

 nate creatures becoming gradually more complicated, 

 as we see in ascending the animal scale. Then em- 

 ploying the two following considerations, he believes 

 he perceives the solution of the problem which has 

 occupied his thoughts. 



He then cites as factors (i) use and disuse ; (2) 

 the movement of internal fluids by which passages 

 are opened through the cellular tissue in which they 

 move, and finally create different organs. Hence the 

 ■movement of fluids in the interior of animals, and the 

 influence of new circumstances as animals gradually 

 expose themselves to them in spreading into every 

 inhabitable place, are the two general causes which 

 have produced the different animals in the condition 

 we now see them. Meanwhile he perceived the im- 

 portance of the preservation by heredity, though he 

 nowhere uses that word, in the new individuals re- 

 produced of everything which the results of the life 

 and influencing circumstances had caused to be ac- 

 quired in the organization of those which have trans- 

 mitted existence to them. 



In the Discours prMminaire, referring to the pro- 



