100 THE BIOLOGICAL PROBLEM OF TO-DAY 



' inner germinal layer ' implies a condition of 

 position winch is created by the invagination. 



In fact, it is impossible, in thinking of the 

 gastrula as in thinking of the blastosphere, to 

 conceive that in the egg, which is a simple cell, 

 there can be preformed by material particles in the 

 nucleus a condition which implies the existence 

 of two layers of cells. 



Thus analysis of a special case leads to the same 

 conclusion as is reached by the general reasoning 

 of the earlier part of this section. 



