26 The Recapitulation Theory and Human Infancy 



ontogeny of a descendant would be a perfectly repeated se- 

 quence of the succession of its adult ancestors, except where 

 the most ancient forms would have been suppressed or omitted 

 from the earliest corresponding embryonic period. This is 

 Cope's " exact parallelism." It would also have the effect 

 of condensing stages without confusing the ancestral order in 

 certain portions of the ontogeny. In case of simple retardation 

 the ontogeny would fail to repeat the most ancient forms, would 

 repeat faithfully the later forms up to the point where the re- 

 tardation left off, and would then fail to repeat stages which 

 the ancestry had recently lost by retardation or successive 

 failure to complete its life cycle. Unequal acceleration would 

 have the effect of " telescoping," or bringing together, stages 

 in ontogeny which had been successive in phylogeny, and to 

 locate later phylogenetic stages before earlier ones. It is ob- 

 vious that, theoretically, this last could confuse the phylogenetic 

 order hopelessly or could even reverse it. 



The relative importance of these several principles, and the 

 validity of recapitulation, becomes therefore a matter of fact. 

 On this point we can but quote competent authority: 



" . . . . there are so many species and genera in the various 

 groups of invertebrates whose ontogeny is simple, progressive, 

 and fairly complete, and whose stages of growth are almost 

 exact repetitions of successive antecedent genera, that it would 

 be impossible to find a student of morphogeny of the brachiopods, 

 the marine mollusks, or the lower crustaceans, that does not 

 believe implicitly in the value of larval stages of these groups 

 as records of their family history." 39 



"In the Cephalapoda, Pelecypoda, Gastropoda, Brachiopoda, 

 Trilobita, Bryozoa, Graptolites, Echinoderms, and Corals, ex- 

 amples are pointed out in which there is clear and unmistak- 

 able evidence of recapitulation." 40 



Hyatt and Cope adduced certain illustrations of accelera- 

 tion and retardation with man and other vertebrates, but since 

 the more recent writers do not emphasize these, it may be as- 

 sumed that the case for recapitulation rests for the group of 

 students here referred to chiefly upon the examples among the 

 invertebrates. 



J. P. Smith, loc. cit., p. 422. 

 Cumings, loc. cit. t p. 337. 



