THE ARGUMENT FROM EMBRYOLOGY 95 



the human skin. Each cell begins its career in an 

 indifferent condition, and gradually acquires the 

 adult peculiarities as it approaches the surface, 

 through removal of the cells lying above it. 



Rudimentary Organs or Vestiges. 



The Recapitulation Theory also affords most 

 valuable assistance in determining the meaning of 

 special points in the structure of animals which other- 

 wise would be hard to understand. More especially 

 is this the case with regard to what are spoken of 

 as "rudimentary organs." These are structures, 

 such as the eye of the mole, or the rudimentary teeth 

 present in whalebone whales at an early develop- 

 mental stage, but got rid of before birth : structures 

 which are constantly present in all members of the 

 species, but which are of no use to their possessors. 

 They cannot be nascent structures — i.e., ones which 

 are in process of formation, but which have not yet 

 become functionally active, for the law of natural 

 selection requires that no structure can be developed 

 and retained by a species unless it either is of direct u 

 use to its possessor, or else has been of use to some 

 of its ancestors. Their presence would be a complete 

 enigma, but for the Recapitulation Theory, which 

 explains them as structures which were formerly of 

 use to the ancestors of the existing animal, and which 

 appear in the latter because of the inherited 

 tendency of all animals to repeat their ancestral 

 history in their own development. Eyes are 

 developed in the mole, although quite useless to it, 



