340 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 Vertcbres. 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, and to increase the size of its parts, up 
to a limit which it brings about. 
“Second law: The production of a new organ in 
an animal body results from the supervention of a 
new want (desoizz) 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 fatio 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.”’ 
