62 THE THEORY OF EVOLUTION 



which he seeks in vain for conclusions of even an 

 approximate certainty." 



Many other equally vigorous and well-deserved 

 criticisms of the embryological method might be 

 cited, but it should be emphasized that these crit- 

 icisms are all directed against the application of the 

 method to the solution of definite and concrete 

 problems of descent and relationship. None of them 

 denies and many strongly affirm that embryology 

 affords some of the strongest and most convincing 

 evidence in favor of the evolutionary theory. 



Let us examine some of this evidence. To begin 

 with, it should be noted that, in following out the 

 ontogeny or individual development, the observer 

 witnesses the formation of something new, not 

 merely the enlargement and unfolding of a pre- 

 existing organism, though the theory of preformation, 

 which was widely accepted in the eighteenth century, 

 looked upon ontogeny precisely in that way, as the 

 growth of a germ which was the miniature of the 

 parent. Such a theory was possible only before the 

 development of microscopic technique had enabled 

 the observer to detect the actual successive steps of 

 change. The egg is a single cell, with the nucleus and 

 all the parts of other undifferentiated cells, though it 

 may be enormously enlarged by the presence of food- 

 yolk. In the hen's egg this food-yolk is quite inert 

 and the activity of development is confined to the 

 minute disc of protoplasm on the outside of the yolk, 



1 E. B. Wilson, in Wood's Hole Biological Lectures, 1894, p. 103. 



