FROM LAMARCK TO ST. HILAIRE 239 



always in direct relation to the employment of 

 these organs. [At another point he expands this 

 into two sub-laws: "In every animal which has 

 not passed the term of its development, the more 

 frequent and sustained employment of each 

 organ little by little strengthens this organ, de- 

 velops it, increases it in size, and gives it a power 

 proportioned to the length of its employment; 

 whereas the constant lack of use of the same 

 organ insensibly weakens it, deteriorates it, pro- 

 gressively diminishes its powers, and ends by 

 causing it to disappear." This is now known as 

 the Law of Use and Disuse, or Kinetogenesis.]) 



Quatrieme loi. — Tout ce qui a ete acquis, 

 trace ou change, dans I'organisation des individus, 

 pendant le cours de leur vie, est conserve par la 

 generation, et transmis aux nouveaux individus 

 qui proviennent de ceux qui ont eprouve ces 

 changements. (All that has been acquired or al- 

 tered in the organization of individuals during 

 their life is preserved by generation, and trans- 

 mitted to new individuals which proceed from 

 those which have undergone these changes.) 



In his earlier work the fourth law was first 

 expressed by Lamarck as follows :^ 



All that Nature has caused individuals to acquire 

 or lose by the influences of circumstances to which 

 they have been long exposed, and consequently by the 



^Philosophie Zoologique, 1873, vol. 1, pp. 235-6. 



