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THE AMERICAN NATURALIST [Vol. XLIII 



the recurrence of which the recapitulation theory was 

 largely built, appear just as early in the embryo of the 

 fish and of Amphioxus, respectively, as in that of a mam- 

 mal. He cites the case of the baleen whale which forms 

 teeth in the embryo like any other mammal, but these 

 beginnings, instead of continuing their development, are 

 absorbed and do not even pierce the gums. The same 

 is true of the dental ridges of birds, where teeth begin 

 to form but soon disappear. 



The evidence presented by the kelps clearly tends 

 to establish this repetition theory of Morgan. The juve- 

 nile forms of the plants have so many points in com- 

 mon that there can be scant doubt but that their ances- 

 tors had similar juvenile forms. It must be added here 

 also that those plants whose development we have traced 

 above are not special cases, but arc only illustrations 

 of the facts common to all kelps. The writer has in 

 his possession full series of several genera which have 

 never been described at length. These and all others 

 which have been worked out follow the same course of 

 development. Among those upon which fairly complete 

 published data are available, may be mentioned: Agarum, 

 I>arber, 'HI); Alaria, Schrader, '03, and others; Cyma- 

 there, Griggs, '07;Eisenia, Setchell, '9Gb, '05a: Lessonia, 

 Eemke, '03; Nereocystis, MaeMillan, '99; Pterygophora, 

 MaeMillan, '02; Saccorhiza, Barber, '89; Thaliasiophvl- 

 lum, Setchell, '05a. 



If we may consider the repetition theory established 

 how much will it help us with our phylogenetic problem! 

 Why should widely diverse forms have ancestors with 

 sum ai embryos ? How were these similar stages acquired 

 and why do they persist? They must be meaningless so 

 ai as phytogeny is concerned, except as they are consid- 

 ered as stages which once led to the development in the 

 adult of the structures which they represent. But why 

 IsTher T °r 10 Characters P ersist and not adult ones! 



ieie any line of demarkation between embryo and 

 adult beyond which the action of heredity changes! 



