Significance of This Law 13 



fetal life a much closer resemblance to those of anthro- 

 poids than during adult life. At a certain stage of 

 development the great toe instead of being parallel to the 

 others forms an angle with their direction as in the apes. 

 In the same way many of the bones of the foot of the 

 newborn infant, in their form, in their respective angles 

 of inclination, etc., resemble very closely those of the 

 climbing foot of the anthropoid apes, particularly of the 

 gorilla. 



In the attempt to see what significance the funda- 

 mental biogenetic law can have for the biologist we can 

 come somewhat nearer to the question by supposing 

 ontogeny to be an exact repetition of phylogeny instead 

 of a rapid resume of it. It is true that it will be necessary 

 later to make some important corrections in this first ap- 

 proximation and to study the significance or cause of the 

 abbreviation and suppression in ontogeny of many phylo- 

 genetic stages ; and this more intimate study will allow us 

 to penetrate further into the innermost nature of the 

 phenomenon. But for the present we desire by this tenta- 

 tive supposition that ontogeny is an exact repetition of 

 phylogeny, to have the great advantage of defining the 

 phenomenon to be studied more simply and precisely, and 

 of making our comprehension of it correspondingly easier. 

 It is by this means, that is by successive degrees of 

 gradual approximation that mechanical, physical, and 

 chemical researches have usually proceeded. 



This first degree of approximation of the fundamental 

 biogenetic law will permit us then to make the tw r o fol- 

 lowing statements : Each stage of the ontogenetic devel- 

 opment of any organism represents exactly one species 

 among the ancestors of that organism. Two species hav- 

 ing a common ancestor have an identical ontogenetic 



