174 Darwin and Embryology 



greater rapidity at the beginning of life than in its later periods. As 

 each of these stages is equal in value, for our present purpose, to the 

 adult phase, it clearly follows that if there is anything in the view 

 that the anatomical study of organisms is of importance in deter- 

 mining their mutual relations, the study of the organism in its 

 various embryonic (and larval) stages must have a greater importance 

 than the study of the single and arbitrarily selected stage of life called 

 the adult. 



But a deeper reason than this has been assigned for the im- 

 portance of embryology in classification. It has been asserted, and is 

 implied by Darwin in the passage quoted, that the ancestral history is 

 repeated in a condensed form in the embryonic, and that a study of 

 the latter enables us to form a picture of the stages of structure 

 through which the organism has passed in its evolution. It enables 

 us on this view to reconstruct the pedigrees of animals and so to 

 form a genealogical tree which shall be the true expression of their 

 T natural relations. 

 I The real question which we have to consider is to what extent the 

 embryological studies of the last 50 years have confirmed or rendered 

 probable this "theory of recapitulation." In the first place it must 

 be noted that the recapitulation theory is itself a deduction from 

 the theory of evolution. The facts of embryology, particularly of 

 vertebrate embryology, and of larval history receive, it is argued, an 

 explanation on the view that the successive stages of development 

 are, on the whole, records of adult stages of structure which the 

 species has passed through in its evolution. AVliether this statement 

 will bear a critical verbal examination I will not now pause to inquire, 

 for it is more important to determine whether any independent facts 

 can be alleged in favour of the theory. If it could be shown, as was 

 stated to be the case by L. Agassiz, that ancient and extinct forms of 

 life present features of structure now only found in embryos, we should 

 have a body of facts of the greatest importance in the present 

 discussion. But as Huxley^ has shown and as the whole course of 

 palaeontological and embryological investigation has demonstrated, 

 no such statement can be made. The extinct forms of life are very 

 similar to those now existing and there is nothing specially embryonic 

 about them. So that the facts, as we know them, lend no sujjport to 

 theory. 



But there is another class of facts which have been alleged in 

 favour of the theory, viz. the facts which have been included in the 



* See Huxley's Scientific Memoirs, London, 1898, Vol. i. p. 303 : " There is no real 

 parallel between the successive forms assumed in the development of the life of the 

 individual at present, and those which have appeared at different epochs in the past." 

 See also his Address to the Geological Society of London (18C2) ' On the Palaeontological 

 Evidence of Evolution,' ibid. Vol. ii. p. 512. 



