134 The Science of Life. 



He believed in it much less than many a modern em- 

 bryologist, such as F. M. Balfour or A. Milnes Marshall. 

 His "laws", as amended by Dr. John Beard, are as 

 follows : 



" There is a stage in the development of every verte- 

 brate embryo, during which, and only then, it resembles 

 the embryo of any other vertebrate in a corresponding- 

 stage in certain general features. But, while it thus 

 agrees exactly with any other embryo in this stage in 

 characters which are common to all vertebrate animals, 

 it differs from the embryo of any other class in certain 

 special class-features, and also from any other embryo 

 of the same class but of a different order, in other and 

 ordinal characters. Immediately before this stage is 

 reached, it begins to put on generic and specific char- 

 acters, and thus it then begins to differ from all other 

 embryos in these." 



Louis Agassiz made one aspect of the recapitulation 

 idea prominent in his teaching, and gave it clear ex- 

 pression in his famous "Essay on Classification" (1859). 

 He rejected the evolutionist interpretation, but insisted 

 on the correspondence between stages in enibryonic 

 development and the grades of differentiation expressed 

 in the classification of living and extinct animals. " It 

 may therefore", he said, "be considered as a general 

 fact, very likely to be more fully illustrated as investi- 

 gations cover a wider ground, that the phases of 

 development of all living animals correspond to the 

 order of succession ,of their extinct representatives in 

 past geological times." His not less illustrious son, 

 Alexander Agassiz, confirmed this in his detailed com- 

 parison between the fossil series of sea-urchins and 

 the early stages in the development of modern forms. 

 "Comparing the embryonic development with the 

 palaeontological one, we find a remarkable similarity." 



In his Facts for Darwin, Fritz Muller expressed the 

 recapitulation doctrine with great clearness, illustrating 

 it from the life-history of Crustaceans. The larval 

 stages which are often so striking, e.g. the common 

 shore-crab, were interpreted as recapitulations of stages 

 in the evolution of the race. 



