28 The Recapitulation Theory and Human Infancy 



and the authority of the writers quoted in this section leave no 

 question of the actuality of many examples of more or less 

 close recapitulation among the invertebrates, at least for shell 

 characteristics as such, and for whole organisms to the extent 

 shells are illustrative of the entire structure of the animal. 4 * 

 Just how general this recapitulation is does not appear, probab- 

 ly this can not be known as yet. The gist of the contentions 

 of the writers in this field seems to be nothing more than that 

 recapitulation constitutes a working principle for genetic classi- 

 fication of very genuine usefulness. There is no disposition to 

 make of it, at the present time at least, a principle of universal 

 application. It is plain that generalizations carried over from 

 this rather circumscribed field of fact to the vertebrate or 

 human territory, and more especially to the human nervous 

 system or mind, can be the sheerest hypothetical possibilities, 

 in view of the complexity of the facts upon this field of their 

 clearest embodiment and of the possible and probable very un- 

 like conditions that have surrounded the evolution of the high- 

 er vertebrate forms. 



12. The Facts of Recapitulation. 



The sketch of the history of the idea of recapitulation thus 

 far drawn shows that speculation and deduction have had no 

 small part in its formulation. The purpose of the present 

 section is to refer somewhat independently to the facts that 

 have been adduced in its support at different times and by 

 various writers. These facts are found to fall into three classes: 

 (a) those derived from a comparison of known ontogenetic 

 and palaeontological data; (b) those of embryonic resemblance 

 among existing types; (c) t 11 " 00 " f stagPfi oxjeatures in ontogeny 



^h«3WJQg jesembIanc £jLa-slagfis_or features^so common to lower" 

 allied living groups as to raise- the -question of an ances^al-xer' 



^ lationship. The facts of the first group are "unequivocal in 

 their significance. Either the parallel exists or does not exist 

 when ontogeny and phylogeny are known and accurately com- 

 pared. The other two types of fact are open to alternative 

 explanations, and give ground for controversy, as we shall see. 



" " The Mollusks would seem, at first sight, bound to supply us with exact phylo- 

 genetic documents by reason of the abundance of their calcerous shells in all geological 

 strata. But. . . the shell is a moiphological organ of little importance." DepSret, 

 loc. cit., p. 48. 



