LAMARCK'S THEORY OF EVOLUTION 



233 



tions which would prevent any one from mitunder- 

 , -standing them." It may be inferred from this that 

 Hie had for some time -previous meditated on this 

 theme. It will now be interesting to see what factors 

 of evolution" Lamarck employed in this'flrst sketch of 

 his theory. 



After stating the distinction^xisting' between the 

 vertebrate and invertebrate animals, and referring to 

 the great diversity of animal forms, he goes on to 

 say that Nature began mth the most siniply organ- 

 ized, and having forthed them, " then with the aid 

 of much time and of favorable circumstances she 

 formed all the othersr' 



" It appeaifS, as I have already said, that time and 

 ' fajwr-able conditions are the two principal "means 

 wljich ■nature has employed in ^ving existence to all 

 her productions. We know that for her time has no 

 Hmit, and that consequently she has it always at her 

 disposal. 



" As to the circumstances of which she has had 

 need and of which she makes use every day in order 

 to cause her productions to vary, we can say that 

 they are in a manner inexhaustible. 



" The essential ones arise from the influence and 

 from all the- environing media (milieux), from the 

 diversity of local causes {diversity des lieux), of habits, 

 of movements, of action, finally of means of living, 

 of preserving their lives, of defending themselves, of 

 multiplying themselves, etc. Moreover, as the result 

 of these different influences the fgrulties, developed 

 and strengthened, by use {usage'), became^diversified 

 by the new habits maintained for long ages, and by 

 slow degrees the structure, the consistence, in a word 

 the nature, the condition of the parts and of the 

 organs consequently participating in all these influ- 



