22 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



literally pulverized by describers of species. It 

 would be an exaggeration to claim that differences 

 such as these are fundamental and exclude all links 

 of relationship between these forms. It may even 

 be said that this want of exactness, this absence of 

 a criterion for the limits of the species, this multi- 

 tude of regional or stratigraphic variations raised 

 by some to the dignity of species, but regarded by 

 others as simple varieties of one specific type, con- 

 stitute at the present day the strongest argument 

 in favour of the transformist hypothesis in palaeont- 

 ology. 



But, after making these reservations against the 

 too absolute ideas of d'Orbigny, the observations of 

 this scholar remain none the less exact in their 

 broad lines, and the sudden replacing of marine 

 faunas when passing from one stage to another, or 

 even from one zone to another zone, must be con- 

 sidered almost a general rule. If the explanation 

 of this great fact by means of successive creations 

 cannot satisfy us from a scientific point of view, 

 we shall have, later on, to seek for it a rational 

 interpretation in the phenomena of the migration 

 of faunas or of migration of environments, similar 

 to those which Cuvier had already made so evident 

 with regard to terrestrial animals. 



