The Recapitulation Theory. 81 



CHAPTER IX. 

 THE RECAPITULATION THKOKY. 



The recapitulation theory has had many vicissitudes both in 

 its application to plants and to animals. The conception has been 

 stated and restated many times in varying terms, but that onto- 

 genetic stages may have a phylogenetic significance has rarely been 

 denied and has more often been implicitly assumed. The principle 

 was tacitly recognized even before Darwin, and he accepted it 

 practically without reserve. Indeed it was one of the foundation 

 stones in his argument for evolution. 



It is desirable also to point out that any theory of recapitulation 

 which is to have any significance in the interpretation of life 

 histories must recognize that in the last analysis recapitulation 

 implies that at some stage in the evolution of any group an increase 

 in the life-cycle took place, by the addition of certain stages. This 

 is in sharp contrast with a germinal change, which necessarily 

 modifies every stage, at least internally as regards nuclear structure, 

 but can hardly be held to add anything to the adult stage of 

 development, or in other words to increase the number of stages 

 in the life-cycle. 



Recapitulation and the alternation of generations in plants. 



As regards plants, it may first be pointed out that the theory 

 of the antithetic alternation of generations, which has been widely 

 adhered to by botanists and has been given its most notable 

 expression in the classic volume of Bower (1908) on The Origin of 

 a Land Flora, implies from the evolutionary point of view a 

 continued lengthening and increase in complexity on the part of 

 the sporophyte, and in seed plants a contemporaneous shortening 

 and simplification of the gametophyte. This theory runs like a 

 golden thread through all the speculations concerning the origin 

 and larger relationships of the main groups of vascular plants, and 

 there is nothing quite corresponding to it among animals. In the 

 able hands of Bower, it implies that the sporophyte generation 

 resulting from the fertilized egg is intercalated between two 

 gametophyte generations and has gradually increased in complexity 

 or length through the Bryophytes, Pteridophytes, GymnospermE 

 and Angiosperms in connection with their gradual transition and 

 adaptation from aquatic or moist to typically terrestrial conditions. 



True, the theory of homologous alternation in plants has also 

 been held, though not so widely. It was for a time based chiefly 



