THE TRANSMUTATION OF SPECIES. 263 



organs upon which new and increased demands were 

 made would undergo a proportionate development in 

 size, and would simultaneously become better fitted for 

 their work. At the same time, they might become 

 modified in form, and thus might become better suited 

 for the purposes for which they were required. On 

 the other hand, the organs which were called into action 

 less frequently than they had previously been, would 

 gradually diminish in size, and might ultimately disappear. 

 By a continuance of this process through many successive 

 generations, the whole organisation of an animal might 

 become profoundly modified. This was therefore the 

 process by which, in the main, Lamarck believed that 

 'species' had been evolved out of other pre-existing 

 forms of life. 



