xlii Trans. Acad. Sci. of St. Louis. 



type, and even of each species. An invisible thread unwinds 

 itself throughout all time across this immense diversity, and 

 presents to us, as a definite result, a continual progress in the de- 

 velopment of which man is the term, of which the four classes 

 of vertebrates are intermediate forms, and the totality of in- 

 vertebrate animals the constant accessory accompaniment." 



These sentences,* written by Agassiz in 1843, show how 

 deeply he was impressed by the overwhelming evidence of order 

 in the succession of living forms, and also that he had thought- 

 fully considered the arguments which had been adduced by 

 advocates of the theory of transmutation of species. At Zurich 

 (1824-1826) he had been a diligent student of Lamarck's Anim- 

 aux sans vertebres, of which, as he could not afford to buy them, 

 he copied two volumes with his own hand. Lamarck's theory 

 of a gradual transformation of species, originating in needs 

 (hesoins) growing out of particular conditions of environment 

 and cumulating in the course of successive generations, had, 

 moreover, been violently opposed and unsparingly ridiculed by 

 Cuvier in all his later years, including the months (December, 

 1831, to May, 1832) spent by Agassiz in his laboratory and in 

 attendance on his lectures. That Agassiz was acquainted with 

 Lamarck's theory, even before he went to Heidelberg, that he 

 held it in mind through the period of his philosophical studies 

 at Munich, that he was cognizant of Cuvier's hostile attitude 

 towards it, and that in his definite rejection of the hypo- 

 thesis (1843) he wrote from profound conviction, can admit of 

 no serious question. In a letter to Professor Adam Sedgwick 

 (June, 1845) he wrote: — ''The idea of a procreation of new 

 species from preceding ones is a gratuitous supposition opposed 

 to all sound physiological notions, and yet it is true that, taken 

 as a whole, there is a gradation in the organized beings of 

 successive geological formations, and that the end and aim of 

 this development is the development of man. But this serial 

 connection of all successive creatures is not material; taken 

 singly these groups of species show no relation through inter- 

 mediate forms genetically derived one from another. The con- 

 nection between them becomes evident only when they are 

 considered as a whole emanating from a creative power, the 

 author of them all." 



* Quoted, in English, from the memoir by Elizabeth Gary Agassiz ; they 

 are taken from Recherches sur les Poissons fossiles — Essai sur la Classification 

 des Poissons — 18me et derniere livraison, Neuchatel, 1843. 



