The Recapitulation Theory in Biology 11 



It was the second parallelism, that between the succession in 

 geological time and the embryonic stages of living representa- 

 tives, that constituted the new phase in the history of recapitula- 

 tion. Of this he said more particularly, 



" These relations, now they are satisfactorily known, may also 

 be considered as exemplifying, as it were, in the diversity of 

 animals of an earlier period, the pattern upon which the phases 

 of the development of other animals of a later period were to be 

 established. They appear now, like a prophecy in those earlier 

 times, of an order of things not possible with the earlier combina- 

 tions then prevailing in the animal kingdom, but exhibiting in a 

 later period, in a striking manner, the antecedent considerations 

 of every step in the gradation of animals." 14 



There is here suggested Agassiz's well known concept of 

 " prophetic types," the facts for which, as well as for his "syn- 

 thetic" and " progressive" types, were so significant to other 

 minds of a genetic relationship he himself refused to acknowledge. 



6. Embryology and Darwinism. 



This correspondence between embryonic stages and the geo- 

 logical succession of animal forms was destined to play an im- 

 portant part with the advent of Darwinism (" Origin of Species," 

 1859). It will be well to indicate at once the three allied uses 

 to which the facts of embryology were put in the development 

 of this theory. They became, in the first place, one main sup- 

 port to the doctrine of descent itself. This was naturally the 

 value attached to them chiefly by Darwin. Once the doctrine 

 was accepted, embryology was employed with all degrees of 

 assurance to determine the affinities of living animals in the 

 interests of a classification based upon genetic relationship. 

 Fritz Miiller was one of the first of a long line of students to 

 demonstrate their usefulness from this viewpoint. Finally, as 

 this classification became elaborated, it made possible the trac- 

 ing back of genealogies, phylogenies, or racial histories, and this 

 was introduced systematically by Haeckel. 



7. Darwin. 



By the time of the sixth edition of the "Origin of Species" in 

 1872, the two applications of the facts of embryology just men- 

 tioned had been made and had received the sympathetic notice 



on Classification, 1857, p. 156. 



