LAMARCK. 



125 



fected by the obligation of the individual to accommo- 

 date itself to the altered conditions of life. Fresh circum- 

 stances elicit fresh requirements and fresh activities. 

 Great weight must be laid on the use or disuse of organs. 

 " In every animal still in the course of development, the 

 more frequent and sustained use of an organ gradually 

 fortifies, develops and enlarges it, and endows it with 

 strength proportional to the duration of this use; while 

 the persistent disuse of an organ imperceptibly weakens 

 and deteriorates it, diminishes its efficiency in an in- 

 creasing ratio, and ultimately destroys it." " And thus," 

 he says, " nature exhibits living beings merely as indi- 

 viduals succeeding one another in generations; species 

 have only a relative stability, and are only transiently im- 

 mutable." 



Lamarck touches upon the struggle of each again 

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

 Natural Selection. He is fully conscious of the two fac- 

 tors, heredity and adaptation, but his theories and con- 

 victions lack the emphasis of detailed evidence. Yet his 

 subtle apprehension of life may be evinced by his in- 

 terpretation of instinct. According to him, all acts of 

 instinct are effected by incitement, exercised upon the 

 nervous system by acquired inclinations (penchans acquis); 

 and these acts, not being the product of deliberation, 

 choice, or judgment, certainly and unerringly satisfy the 

 requirements experienced and the inclinations resulting 

 from habit. But if these inclinations to maintain the 

 habit and renew the actions related to them, are once 

 acquired, they are henceforward transmitted to the indi- 

 viduals by means of reproduction, which maintains the 

 structure and the disposition of the parts in the condition 



