8 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



edged physiological facts, the former traceable to prop- 

 agation, the latter to the nutrition of organisms." 

 Apart from the statement that adaptation is traceable 

 "to the nutrition of organisms," we find nothing in 

 Haeckel's earlier writings which attempts the ex- 

 planation of the origin of variations, beyond the gen- 

 eral position assumed by Lamarck. The distinctive 

 merit of Haeckel is his formulation of phylogeny. Much 

 of this was speculative at the time he wrote, but so far 

 as the Vertebrata are concerned, it has been largely 

 confirmed by subsequent discovery. 



Up to this period, the form in which the doctrine 

 of evolution had been presented, was general in its 

 application ; that is, without exact reference to the 

 structural definitions of natural taxonomic groups. No 

 attempt was made to show the modes of the origin of 

 any particular class, order, or genus, and only in the 

 most general way in the case of a few species, by Mr. 

 Darwin. Phylogeny was untried, except by Haeckel; 

 and this distinguished author did not attempt to ac- 

 count specifically for the origins of the divisions whose 

 filiations he set forth. 



In the year in which Haeckel's work above cited 

 appeared, Professor Hyatt of Boston and myself took 

 the first step towards the formulization of a rational 

 theory of the origin of variation, which should accord 

 with specific examples of taxonomy. Quite indepen- 

 dently, we selected the simple series presented by the 

 characters of genera in their natural relations, Hyatt 

 in the cephalopodous Mollusca, and I in the Batrachia 

 Salientia. It is probable that Hyatt's l article was pub- 

 lished shortly before mine. He says of the genera of 

 Cephalopoda : "In other words, there is an increasing 



I Memoirs Boston Society Natural History, 1866, p. 193. 



