LAMARCK’S THEORY OF DESCENT 295 
“ Assuredly, if these expressions should be taken 
literally, I should be accused of an error; for what- 
ever may be the circumstances, they do not directly 
cause any modification in the form and structure of 
animals. 
“But the great changes in the circumstances bring 
about in animals great changes in their needs, and 
such changes in their needs necessarily cause changes 
in their actions. Now, if the new needs become con- 
stant or very permanent, the animals then assume new 
habits, which are as durable as the needs which gave 
origin to them. We see that this is easily demon- 
strated and even does not need any explanation to 
make it clearer. 
“Tt is then evident that a great change in circum- 
stances having become constant in a race of animals 
leads these animals into new habits. 
“Now, if new circumstances, having become per- 
manent in a race of animals, have given to these 
animals new /adits—that is to say, have led them to 
perform new actions which have become habitual— 
there will from this result the use of such a part by 
preference to that of another, and in certain cases 
the total lack of use of any part which has become 
useless. 
“Nothing of all this should be considered as a 
hypothesis or as a mere peculiar opinion; they are, 
on the contrary, truths which require, in order to be 
made evident, only attention to and the observation 
of facts. 
““We.shall see presently by the citation of known 
facts which prove it, on one side that the new wants, 
having rendered such a part necessary, have really by 
the result of efforts given origin to this part, and ‘that 
as the result of ‘its sustained use it has gradually 
strengthened it; developed, and has ended incon: 
siderably incrcasing its size; on the other side we 
shall see that, in certain cases, the new circumstances 
