66 LOUIS AGASSIZ. [CHAP. xvi. 



siz to natural history during his life in America. It 

 contains the last great discovery he made ; namely, 

 that " the changes which animals undergo during their 

 embryonic growth coincide with the order of succession 

 of the fossils of the same type in past geological ages." 



If the influence exerted by the " Essay ' was not so 

 great as it should have been, it was due to adverse 

 circumstances which it was impossible to foresee and 

 prevent. During his stay in Europe, Agassiz's researches 

 were mainly palrcontologic, with the study of glaciers 

 as a sort of recreation. His true zoological studies were 

 confined to fresh-water fishes, and even these studies he 

 did not carry very far. In America, on the contrary, 

 he devoted almost all his time to zoology and to embry- 

 ologic researches, almost entirely abandoning palaeontol- 

 ogy and glaciers ; and it required ten years of hard and 

 continuous work, mainly with the microscope, to enable 

 him to master the purely zoological part of living 

 animals, and explain its harmony with the palaeontology. 

 It is not just to reproach him, as has sometimes been 

 done, with the fact that his work on classification came 

 too late by ten years ; for it was impossible for him to 

 collect sooner the immense quantity of materials re- 

 quired, though, of course, if it had been published ten 

 years earlier, it would have exerted a greater influence 

 on his contemporaries. 



On the other hand, the publication of Darwin's 

 " Origin of Species," only two years after the issue of 

 Agassiz's " Essay on Classification," distracted the at- 

 tention of a certain number of savants, who seized this 

 opportunity to discuss and checkmate the theory of 



