LAMARCK. 125 



short as to give rise to the vulgar and false hypothesis 

 of stability and immutability. The transformation is 

 effected by the obligation of the individual to accom- 

 modate itself to the altered conditions of life. Fresh 

 circumstances elicit fresh requirements and fresh activi- 

 ties. Great weight must be laid on the use or disuse 

 of organs. " In every animal still in the course of de- 

 velopment, the more frequent and sustained use of an 

 organ gradually fortifies, developes and enlarges it, and 

 endows it with strength proportional to the duration of 

 this use ; while the persistent disuse of an organ imper- 

 ceptibly weakens and deteriorates it, diminishes its effi- 

 ciency in an increasing ratio, and ultimately destroys it." 

 " And thus," he says, " nature exhibits living beings 

 merely as individuals succeeding one another in genera- 

 tions ; species have only a relative stability, and are 

 only transiently immutable." 



Lamarck touches upon the struggle of each against all 

 (I. 99, and elsewhere), but does not discover the term 

 Natural Selection. He is fully conscious of the two 

 factors, heredity and adaptation, but his theories and 

 convictions lack the emphasis of detailed evidence. 

 Yet his subtle apprehension of life may be evinced by 

 his interpretation of instinct. According to him, all 

 acts of instinct are effected by incitement, exercised 

 upon the nervous system by acquired inclinations 

 {penchaiis acquis) ; and these acts, not being the product 

 of deliberation, choice, or judgment, certainly and un- 

 erringly satisfy the requirements experienced and the 

 inclinations resulting from habit. But if these inclina- 

 tions to maintain the habit and renew the actions 

 related to them, are once acquired, they are henceforward 



