The Recapitulation Theory in Biology 35 



- >.„.<-»*'•' 

 in all three of its main implications. The order of appearance 



of characters is not uniformly, or even commonly, that required 

 by recapitulation, which is first those representative of the 

 order, and then in succession, of the family, genus, species. 

 In ^he second place, embryonic resemblance in comparable 

 stages does not vary directly with remoteness of kinship, but 

 shows often very great divergence from this rule, indicating 

 unlike careers in lines of descent in the same group and there- 

 fore great diversity in the appearance of variation during de- 

 velopment, at any period, and not only at the adolescent or 

 adult end of ontogeny. Finally, where resemblance does ex- 

 ist, it is not identity, nor even close, implying that the effect 

 of variation upon the same ancestral structure has not been 

 the same in allied lines of descent, but has been productive of 

 new structures, suggesting perhaps in broad outlines the an- 

 cestral structure, but still variant in every case, and essenti- 

 ally so. 



What is left for von Baer's law is the "family resemblance." 

 But family resemblance does not imply recapitulation. It 

 means at most a common ancestor. 66 This common ancestor 

 may have had his ontogeny determined in any way, recapit- 

 ulatory or other. That this family resemblance may often be 

 striking without implying recapitulation is well shown in a 

 recent statement. The Nauplius larva is common to many 

 Crustacea. "But it is not in the least justifiable to deduce, 

 as some have attempted, that the Nauplius larva represents 

 the adult ancestral form from which the Crustacea as a whole 

 have sprung." " The Zoaea larva is similarly characteristic of 

 many widely separated Crustacean groups, nevertheless "it 

 cannot possibly be looked upon as representing the adult an- 

 cestral type of these animals." M 



Again, "A larval form, yet more widely spread than either of 

 the Crustacean larvae mentioned, is the Trochosphere larva, 

 characteristic of Annelids of all kinds and curiously enough of 

 some Mollusks .... which in the adult state are entirely 



""When we recognize a larval or embryonal form as characteristic for a whole 

 animal group, we may not conclude therefrom that necessarily a similar phylogenetic 

 stage is represented by the same. We are justified only in the conclusion that the 

 ancestral foim of this animal group had possessed that characteristic developmental 

 stage." Hatschek, quoted by Montgomeiy, loc. cit., p. 185. 



« Smith, Primitive Animals, 1912, p. 64. 



" Ibid., p. 65. 



