LAMARCK'S THEORY OF DESCENT 



29s 



" 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. 



" It is then evident that a great change in circum- 

 stances having become constant in a race of aniftials 

 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 habits — 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 orderto 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 in con- 

 siderably increasing its size ; on the other side we 

 shall see that, in certain cases, the new circumstances 



