36 The Recapitulation Theory and Human Infancy 



different in their whole organization from worms of any de- 

 scriptive. This fact implies that the Trochosphere is an ex- 

 ceedingly ancient type of larva, which must have been possessed at 

 some period by the common ancestor of the Annelids and Mol- 

 lusks . . . There is however nothing to support the view 

 that the Trochosphere in any way represents the common an- 

 cestor of the Annelids and Mollusks. . ."" 



"We cannot however press the argument too far and say 

 that no larval form ever represents an adult ancestral form. 

 Every case must be judged on its own merits after taking into 

 account all the available evidence to be derived from the com- 

 parative study of related forms. Thus it seems indubitable 

 that the so-called Mysis larva, a stage assumed by [many mem- 

 bers of a group of Crustaceans] after the Zoaea .... does 

 very closely represent an adult ancestral form, the actual ex- 

 istence of which is nearly realized by the primitive Anaspides 

 and Schizopod shrimps. Here we are dealing with a late 

 larval form just before the adult structure is attained, and it 

 would appear not to have had time to have been profoundly 

 modified in accordance with larval existence. It would seem, 

 therefore, that we are more likely to meet with actual adult 

 ancestral types in the late larval or developmental stages of 

 fairly closely related animals, which have not had time to be 

 secondarily modified, than in the very early stages of more 

 remotely related forms, although these, in accordance with 

 von Baer's law, may show many points of resemblance which 

 are lost in the adults." 60 



The writer from whom these sentences are taken is able to 

 accept von Baer's law by a loose construction of it: "his [von 

 Baer's] statement was that in any two or more related animals 

 the further back we go in their developmental history from the 

 egg the more do they resemble one another. In this form 

 it must be admitted that von Baer's law holds good with very 

 few exceptions " 61 



This statement may be compared with those of the author- 

 ities already quoted. It appears that even on this loose con- 

 struction of the meaning of von Baer's formulae there is no 

 settled unanimity of opinion among biologists. These dis- 

 crepancies, however, do not affect the essential significance 

 of the law for recapitulation, for as to this all the writers quoted 

 agree in that embryonic likenesses do not of themselves imply 



» Smith, Primitive Animals, 1912, pp. 68, 70. 

 •° Ibid., pp. 66-68. 

 " Ibid., p. 58. 



