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do with the laws of development and inheritance. To the former class 

 belong such critics as Von Baer, and to the latter class such as Hatschek, 

 His, Hurst, Montgomery and others. 



In making this statement I am aware that paleontologists sometimes 

 compare true embryonic stages with adult stages of pre-existing types. 

 As examples of this we might cite the comparison of the larval stage of 

 Antedon with adult Paleozoic crinoids, as mentioned by Zittel; and the 

 classic attempt of Beecher to reconstruct the ancestor of the Brachiopoda 

 by a comparison of the phylembryonic stages of a representative series of 

 genera of recent and fossil brachiopods. Nevertheless by far the greater 

 number of comparisons that have been instituted by paleontologists have 

 been between epembryonic stages of individuals and adult stages of older 

 forms. Such comparisons are those of Hyatt, Branco, Karpinsky, Wiirten- 

 burger, Bnckman, Neuinayr, Smith, Beecher, Clarke and others among the 

 Cephalopoda ; of Beecher and Schuchert, Raymond, Greene and Cumings 

 amoug the Brachiopoda ; of Jackson among the Pelecypoda ; of Grabau 

 and Burnett Smith among the Gastropoda; of Lang and Cumings among 

 the Bryozoa ; of Ruedemann among the graptolites ; and of Beecher, 

 Girty, Lang and others among the corals. To many of these researches I 

 shall refer later. 



I am also not unmindful of the fact that many of those who are not 

 primarily paleontologists recognize the fact that development does not 

 terminate with the completion of the embryonic stages, and that recapitu- 

 lation may be legitimately looked for in epembryonic as well as embryonic 

 stages, or that it may be sought iu epembryonic stages, even though masked 

 or falsified in embryonic stages. It is true, of course, that some speak of 

 a comparison of ontogeny and phylogeny when, judging by the context, 

 they mean a comparison between embryogeny and phylogeny. There arises 

 here a question of definition : does the biogenetic law mean that the 

 ontogeny is a recapitulation of the phylogeny, or does it mean that the 

 embryogeny is a recapitulation of the phylogeny? If we take the general 

 consensus of opinion we shall find for the former definition, and if we 

 take the words of Haeckel, whose statement of the law is the one usually 

 quoted, we shall again find for the former definition. I believe that, as 

 a matter of fact, no one would maintain that the second definition is cor- 

 rect, however much he might forget in his studies to take the epembryonic 

 stages into consideration. 



