EDITOR'S INTRODUCTION xxix 



in nature. He never questioned variation itself, but rather the sig- 

 nificance that advocates of development attributed to it. Equating 

 change in nature with change in individuals, he affirmed that such 

 individual variation never influenced the permanence of the type. 

 Thus he could write, "I have seen hundreds of specimens of . . . 

 our Chelonians, among which there were not two identical. . . . 

 truly, the limits of this variability constitutes one of the most im- 

 portant characters of many species." (p. 66) Yet he could assert with 

 equal conviction that "it was a great step in the progress of science 

 when it was ascertained that species have fixed characters and that 

 they do not change in the course of time." (p. 58) 



Denying the significance of individual variation, Agassiz never- 

 theless attributed much importance to the development of the in- 

 dividual. Embryology, therefore, furnished "the most trustworthy 

 standard to determine the relative rank among animals." Emphasis 

 upon ontogenetic transformation led Agassiz to admire the work of 

 Karl Ernst von Baer, the modern founder of embryological investi- 

 gation. The labors of von Baer impressed him as proving that while 

 individuals experienced a series of transformations, they "never 

 produce anything different from the parents ... all reach through 

 a succession of unvarying changes, the same final result." Develop- 

 ment was therefore a phenomenon identified solely with the life 

 history of the individual, and such finite events could not effect the 

 type, which was fixed and final. All so-called "change" was simply a 

 "cycle of growth." Life cycles "revolve forever upon themselves,* 

 returning at appointed intervals to the same starting-point and re- 

 peating through a succession of phases the same course." In so 

 defining "evolution" Agassiz also adopted another, equally inclusive 

 viewpoint toward change in nature. He persisted in equating change 

 in individuals or ontogeny, with phylogeny, or the history of the 

 entire race or group. Thus the phases of development in living 

 animals were considered recapitulations of the order of succession 

 of their extinct ancestral forms. The history of the type was therefore 

 the "cause" of the history of the individual, and such recapitulation 

 of phylogeny in ontogeny demonstrated that 



the leading thought which runs through the succession of all organized beings 

 in past ages is manifested again in new combinations in the phases of the de- 

 velopment of the living representatives of these different types. It exhibits every- 



