KM 



THE AMERICAN NATURALIST [Vol. XLIII 



heavy surf and the drying incident to living above the 

 tide mark. At the same time it has such a high degree 

 of variability in its whole structure that it is difficult to 

 pick out characters sufficiently fixed to be of use in de- 

 scribing it. There seems to be no good reason to doubt 

 its primitive position. 



Taking all the evidence into consideration, it seems 

 to the writer that we are bound to conclude that though 

 organisms are subject to adaptation at any stage of their 

 life cycles and may gradually cut out superfluous stages, 

 yet, except as some such tendency has operated to change 

 the heritage, the development of the individual does re- 

 capitulate the history of the race. The degree of corre- 

 spondence of any individual cycle with its ancestral his- 

 tory is various in different cases but may be very close. 

 Eecapitulation must take place if there is any force which 

 tends to make offspring like parent, if heredity is of any 

 importance in moulding the forms of organisms. On 

 the other hand, if there he any variability or transmuta- 

 tion of individuals in stages other than the adult end 

 stages of their life cycles, the recapitulation can not be 

 perfect, but must be marred at every stage where second- 

 ary change has taken place. The extent to which any 

 individual will recapitulate its phylogeny must therefore 

 depend on the balance maintained between these two 

 forces in the given case. The value of a study of on- 

 togeny for the taxonomist or phylogenist will depend al- 

 together on the facts of the special case. In each case 

 the evidence must be weighed before a conclusion can 

 be reached. Ontogeny may be of greater or less worth 

 in the attempt to build a rational system of nature. But 

 variable as its utility may be in different cases, the re- 

 capitulation theory states a fundamental law of a tend- 

 dency of the embryogeny and must be considered as one 

 of the several interacting tendencies which together con- 

 trol the development of animals and plants. 



