214 



LAMARCK, HIS LIFE AND WORK 



d'un mime type." These views he did not abandon, 

 nor, on the other hand, did he actively promulgate 

 them. It was not until thirty years later, in his 

 memoir on the anatomy of the gavials, that he began 

 the series of his works bearing on the question of 

 species. In 1831 was held the famous debates between 

 himself and Cuvier in the Academy of Sciences. But 

 the contest was not so much on the causes of the 

 variation of species as on the doctrine of homologies 

 and the unity of organization in the animal kingdom. 



In fact, Geoffroy did not adopt the views peculiar 

 to his old friend Lamarck, but was rather a follower 

 of Buffon. His views were preceded by two premises. 



The species is only " fix^ sous la raison du m.aintien 

 de r^tat conditiomiel de son ^nilieii ambiant." 



It is modified, it changes, if the environment 

 {milieu ambiant) varies, and according to the extent 

 {selon la port^e) of the variations of the latter.* 



As the result, among recent or living beings there 

 are no essential differences as regards them — " cest 

 le meme cours d'^vdnements," or "la mime marche 

 d' excitation." \ 



On the other hand, the monde am,biant having 

 undergone more or less considerable change from 

 one geological epoch to another, the atmosphere 

 having even varied in its chemical composition, and 

 the conditions of respiration having been thus modi- 

 fied, X the beings then living would differ in structure 

 from their ancestors of ancient times, and would 



* Etudes progressives d'un Naturaliste, etc., 1835, p. 107. 

 f Ibid. 



X Sitr i' Influence du Monde ambiant pour modifier les Formes 

 animaux {Mdmoires Acad. Sciences, xii., 1833, pp. 63, 75). 



