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 résumé 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 two 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 
