296 LAMARCK, HIS LIFE AND WORK 



and new wants having rendered such a part wholly- 

 useless, the total lack of use of this part has led to 

 the result that it has gradually ceased to receive the 

 development which the other parts of the animal 

 obtain ; that it gradually becomes emaciated and 

 thin ; and that finally, when this lack of use has been 

 total during a long time, the part in question ends in 

 disappearing. All this is a positive fact ; I propose 

 to give the most convincing proofs. 



" In the plants, where there are no movements, and, 

 consequently, no habits properly so called, great 

 changes in circumstances do not bring about less 

 great differences in the development of their parts ; 

 so that these differences originate and develop cer- 

 tain of them, while they reduce and cause several 

 others to disappear. But here everything operates 

 by the changes occurring in the nutrition of the plant, 

 in its absorptions and transpirations, in the amount of 

 heat, light, air, and humidity which it habitually re- 

 ceives ; finally, in the superiority that certain of the 

 different vital movements may assume over others. 



" Between individuals of the sam.e species, some of 

 which are constantly well nourished, and in circum- 

 stances favorable to their entire development, while 

 the others live under reversed circumstances, there is 

 brought about a difference in the condition of these 

 individuals which gradually becomes very remarkable. 

 How many examples could I not cite regarding ani- 

 mals and plants, which would confirm the grounds for 

 this view ! Now, if the circumstances remain the 

 same, rendering habitual and constant the condition 

 of individuals badly fed, diseased, or languishing, their 

 internal organization becomes finally modified, and 

 reproduction between the individuals in question 

 preserves the acquired modifications, and ends in giv- 

 ing rise to a race very distinct from that of the in- 

 dividuals which unceasingly meet with circumstances 

 favorable to their development. 



