LAMARCK. i5j 



expanded. This is characterized by a clear and 

 beautiful style, and by a logical development of the 

 argument, in which Lamarck's whole scheme of 

 Evolution is gradually unfolded. His theory was 

 never developed beyond this point, althou-Ji he 

 restated it in a more condensed form in the intro- 

 duction to both editions of his Histoirc dcs Aiii- 

 maux sans Verfebres between 1816 and 1S22. 



The Philosophie Zoologique shows that three 

 truths had now come to him from his labours in 

 Botany and Zoology, and presumably from his 

 wider readings of Buffon's earlier writings, of 

 Linnaeus, and of the Greeks, to whom he makes 

 allusion. These are, first, the certainty that sj)e- 

 cies vary under changing external influences; 

 second, that there is a fundamental unity in 

 the animal kingdom ; third, that there is a ])rogres- 

 sive and perfecting development. Among the 

 influences of environment he cites the cases of the 

 supposed influence of water upon plants and ujDon 

 the lower animals; the influence of air in forming 

 the entire respiratory system of birds; the influence 

 of light upon plants, directly upon the colouring of 

 animals, and upon the development and degenera- 

 tion of eyes, and the influences of heat. The main 

 influences come under the law of Use and Disuse, 

 for he believes that Nature does not effect her 

 changes directly, but through the reaction of ani- 

 mals to their environment. 



He thus differs widely from Buffon : " Lack of em- 



M 



