LIFE ON THE EAETH. 193 



'These assertions are purely gratuitous. At the 

 present time such deviations are not producible even 

 by means of art, and it is known by examination of 

 the fossils of the later formations, as well as by the 

 comparison of the most ancient examples with their 

 living analogues, that the forms remain unalterable/ 



So Agassiz, after that complete survey of Fossil 

 Fishes, which has earned him the perpetual gratitude 

 of geologists, says on the question of the diversity of 

 species due to development: 'We must necessarily 

 rise to a higher cause, and recognize more powerful 

 influences, exercising on the whole of nature a more 

 direct action, if one wishes not always to move in a 

 vicious circle. For my part, I am convinced that 

 species have been created successively at different 

 epochs; and that the changes which they have 

 suffered during a geological period are but of second- 

 ary importance, and depend only on their greater 

 or less fecundity, and on migrations subordinated to 

 the influences of the period.' 



On the same side must be ranked the great 

 authority of Cuvier, 



clarum et yenerabile nomen. 



'There is no proof that all the differences which 

 now distinguish organized beings are of such a nature 

 as to have been produced by circumstances. All that 

 has been advanced on this subject is hypothetical; 



Ii. L. n 



