290 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 same 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 ‘erounds 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. 
