GEOFFROY ST. HILATRE. II7 



the transformation of animal and vegetable species was less 

 effected by tlie action of the organism itself (by habit, 

 practice, use, or disuse of organs) than by the "monde 

 ambiant," that is, by the continual change of the outer 

 world, especially of the atmosphere. He conceives the 

 organism as passive, in regard to the vital conditions of the 

 outer world, while Lamarck, on the contrary, regards it 

 as active. Geoffroy thinks, for example, that birds origi- 

 nated from lizard-like reptiles, simply by a diminution of 

 the carbonic acid in the atmosphere, in consequence of which 

 the breathing process became more animated and energetic 

 through the increased proportion of oxygen in the atmosphere. 

 Thus there arose a higher temperature of the blood, an 

 increased activity of the nerves and muscles, and the scales 

 of the reptiles became the feathers of the birds, etc. This 

 conception is based upon a correct thought, but although 

 the change of the atmosphere, as well as the change of every 

 other external condition of existence, certainly effects 

 directly or indirectly the transformation of the organism, 

 yet this single cause is by itself too unimportant for such 

 effects to be ascribed to it. It is even less important than 

 practice and habit, upon which Lamarck lays too much 

 stress. Geoffroy 's chief merit consists in his having vindi- 

 cated the monistic conception of nature, the unity of 

 organic forms, and the deep genealogical connection of the 

 different organic types in the face of Cuvier's powerful 

 influence. I have already mentioned in the preceding 

 chapter (pp. 87, 88) the celebrated disputes between the two 

 great opponents in the Academy of Paris, especially the 

 fierce conflicts on the 22nd of February, and on the 19th of 

 July, in which Goethe took so lively an interest. On that 



