The Cellular Basis 177 



tinct individuals in every generation, each of which has its own 

 peculiar value, the game of heredity becomes vastly more complex 

 than any game of cards. 



This illustration may serve to make plain the fact that in the 

 process of maturation and fertilization there is this shuffle and deal 

 of the chromosomes, with the result that every oosperm and every 

 individual which develops from it is different from every other 

 one. 



Germ Cells as Specific as Persons. This conception of the spe- 

 cificity of every germ cell, as well as of every developed individ- 

 ual, sets the whole problem of heredity and development in a clear 

 light. The visible peculiarities of an adult become invisible as 

 development is traced back to the germ, but they do not wholly 

 cease to exist. Similarly the multitudinous complexities of an 

 adult fade out of view as development is traced to its earliest 

 stages, but it is probable that they are not wholly lost. In short, 

 the specificity of the germ applies not merely to those things in 

 which it differs from other germs, but also to characters in which 

 it resembles others; in short, to hereditary resemblances no less 

 than to hereditary differences. 



The mistake of the doctrine of preformation (see p. 57) was 

 in supposing that germinal parts were of the same kind as adult 

 parts; the mistake of epigenesis was in maintaining the lack of 

 specific parts in the germ. The development of every animal and 

 plant consists in the transformation of the specific characters of 

 the germ into those of the adult. From beginning to end de- 

 velopment is a series of morphological and physiological changes 

 but not of new formations or creations except in so far as new 

 structures or functions appear as a result of "creative synthesis." 

 It is only the incompleteness of our knowledge of development 

 which allows us to say that the eye or ear or brain begins to 

 form in this or that stage. They become visible at certain stages, 

 but their real beginnings are indefinitely remote. 



