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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, Buckman, Neumayr, Smith, Beecher, Clarke and others among the 
Cephalopoda; of Beecher and Schuchert, Raymond, Greene and Cumings 
among 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 cf 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 in 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. 
