DA LAMARCK, HIS LIFE AND WORK 
d’un méme 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 “ fivé sous la raison du matntien 
de 1 état conditionnel de son milieu ambtant.” 
It 4s: modihed, it changes, 1f the environment 
(milicu ambiant) varies, and according to the extent 
(selon la portéc) of the variations of the latter.* 
As the result, among recent or living beings there 
are no essential differences as regards them—“ c'est 
le méme cours a’ événements,’ or “la méme marche 
ad’ excitation.’ + 
On the other hand, the monde ambiant 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, + 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. 
+ Thid, 
t Sur Ll’ Influence du Monde ambiant pour modifier les Formes 
animaux (Mémoires Acad. Sciences, xii., 1833, pp. 63, 75). 
