No. 506] KELPS AND RECAPITULATION THEORY 97 



Nereocystis, Tliallasiophyllum and Microcystis. One 

 might imagine other forms npon which each of these 

 might have been built up more directly than on this 

 one. This is particularly true in the case of Egregia and 

 Hedophyllum, where, while the young are indistinguish- 

 able, the course of development is diametrically opposed. 

 Egregia dwarfs the lamina and becomes nearly all stipe; 

 Hedophyllum obliterates the stipe and becomes a sessile 

 lamina. If ontogeny represents merely stages physio- 

 logically necessary to the attainment of the adult form, 

 why should Hedophyllum produce a stipe at all.' 



Similar conditions are presented by very many other 

 cases, especially among animals where some organ is de- 

 veloped in the embryo which later disappears without 

 being of service either to the embryo or to the adult. 

 Such cases have in the past been the main evidence 

 brought forward for the recapitulation theory, as it has 

 been supposed they were explicable only on the basis of 

 a recapitulation of the phylogeny. Familiar examples 

 are cited by Morgan (see below), and many more might 

 be added. 



Not all who attack the recapitulation theory go so far 

 as to discard it altogether. Many recognize in it a truth 

 and seek to modify it to fit certain facts. The form 

 which has the largest number of adherents is perhaps 

 that proposed by Morgan ('03), who believes that ani- 

 mals in their ontogeny repeat not the adult, but the em- 

 bryonic stages of their ancestors; that the presence of a 

 certain structure in the embryo means that the ances- 

 tors of the species to which the organism belongs had 

 similar embryonic stages. This he calls the "Repetition 

 Theory." Much of the evidence which the zoologists 

 bring forward in favor of such a modification as against 

 any broader application is so conclusive, one must ac- 

 knowledge that such is a correct statement of the facts 

 in the particular cases cited, whatever the general law 

 of development may be. Morgan calls attention to the 

 fact that the gill-clefts and the notochord, structures on 



