The Recapitulation Theory in Biology 57 



lose without ceasing altogether to be an aquatic larva. The 

 larva is therefore much more of an adaptation than a recapitu- 

 lation." 94 



This he finds generally true of flat fish and other animals with 

 such larvae, so that he feels warranted in making the statement 

 that "Recapitulation does not occur. . . .except when the extern- 

 al condition to which the ancestral structure was adapted con- 

 tinues to act at an early period of life." 95 



Macbride, employing Sedgwick's theory, gives many illus- 

 trative cases and compares the conditions of larvae and embryos. 

 Ancestral traces are found in the vast majority of larvae. 9 ' 



(4) We are thus led to the fourth position assumed toward 

 recapitulation. It is close to that of Sedgwick just described. 

 The greater part of the resemblance between descendants and 

 ancestors is, where it exists at all, between their ontogenies. 

 Nevertheless, cases exist, more especially among larvae, of the 

 ontogenetic retention of adult characters. This, it is to be 

 noted, agrees with the results of the Hyatt school of palaeontol- 

 ogists. In their impressive array of facts, as summarized by 

 Curnings, it was the post-embryonic and not the embryonic 

 stages that made the basis of comparison. 97 



Grigg's acceptance of both the view of ontogenetic repetition 

 and that of ontogenetic-adult repetition, has been noted. A 

 sentence from this writer will serve as a fitting conclusion to 

 this report of opinion: "In each case the evidence must be 

 weighed before a conclusion can be reached." 



15. Summary and Conclusions. 



The history of the recapitulation theory may be briefly re- 

 viewed. In the early references to the idea at the beginning 

 of the nineteenth century, when the science of embryology 

 was taking form, the attention of observers was caught by re- 

 semblances which evoked the belief that individual develop- 



M Science Progress, VI, 1897, p. 489. 



Ibid., p. 508. 



The functional character of embryonic and rudimentary embryonic structures is 

 illustrated and enlarged upon by Peter, Ueber die biologische Bedeutung embryonaler 

 und rudimenta.rer Organe, Arch, fur Entwickelungsmechanik, 1910. 



Sedgwick's Theory of the Embryonic Phase of Ontogeny, etc.. Quart. Journ. 

 Micros. Sci., XXXVII, 1894-95. 



' See page 27. 



