962 Influence of circumstances on the Actions of Animals. 
- expressions were taken literally, an error would be ascribed to me; 
for, whatever the circumstances might be, they would not produce 
directly any modification whatever in the form and organization 
of the animals. 
But great changes in circumstances bring among animals great 
changes in their. wants, and changes in their wants necessarily 
bring parallel modifications into their actions. Now, if the new 
wants become constant or very lasting, the animals will adopt new 
habits, which are as permanent as the wants which produced them. 
This is a fact easy of demonstration, such as requires no explanation 
to be appreciated. 
It is then evident that a great change in circumstances becom- 
ing constant in a race of animals, entails upon these animals new 
habits, 
Now, if new circumstances becoming permanent with a race of 
animals, have given to these animals new habits; that is to say, 
have forced them to new actions, which have become habitual, 
the consequence will be the employment of some part, in pref- 
erence to some other part, and in certain cases the total lack 
of employment of a part which has become useless. 
Nothing of all this should be considered as an hypothesis, or a8 
a private opinion; they are, on the contrary, truths which, in order 
to be rendered evident, require only attention and observation of 
facts. We shall see directly by the citation of known facts, which 
prove, on one side, that new wants, having rendered a certain p 
necessary, have really by repeated efforts created this part, and in 
consequence of repeated employment have little by little strength- 
ened and developed them, and have resulted in a considerable 
increase of size. On the other hand, we shall see that in certain 
cases new circumstances and new wants having rendered a certain 
part entirely useless, the total lack of employment of that part has 
caused its growth gradually to cease; that it becomes small and 
attenuated little by little, and that finally, when this lack of 
employment has been total for a long time, the part in question 
disappears. . : 
All this is certain, and I now propose to give the most convin- 
cing proof. In vegetables, which have no movements, and in conse- 
quence no habits, properly speaking, great changes of circumstances 
