346 



LAMARCK, HIS LIFE AND WORK 



" Each part necessarily is obliged to change, and to 

 cease to be one in order to constitute another, with 

 interests opposed to those of all ; and if it has the 

 power of reasoning it finds this whole imperfect. In 

 reality, however, this whole is perfect, and completely 

 fulfils the end for which it was designed." 



The last work in which Lamarck discussed the 

 theory of descent was in his introduction to the 

 Animaux sans Vertebres. But here the only changes 

 of importance are his four laws, which we translate, 

 and a somewhat different phylogeny of the animal 

 kingdom. 



The four laws differ from the two given in the 

 Philosophie zoologique in his theory (the second law) 

 accounting for the origin of a new organ, the result 

 of a new need. 



" First law : Life, by its proper forces, continually 

 tends to increase the volume of every body which 

 possesses it, apjd to increase the size of its parts, up 

 to a limit which it brings about. 



" Second /«w\:^The production of a new organ in 

 an animal body results from the supervention of a 

 new want {besoiri) which continues to make itself felt, 

 and of a new movement which this want gives rise to 

 and maintains. 



" Third law: The development of organs and 

 their power of action are constantly in ratio to the 

 employment of these organs. 



" Fourth law : Everything which has been acquired, 

 impressed upon, or changed in the organization of 

 individuals, during the course of their life is preserved 

 by generation and transmitted to the new individuals 

 which have descended from those which have under- 

 gone those changes." 



