THE EVOLUTION OF MAN 



cells. In the center of this lump a hollow space 

 is formed, and a closed hollow bladder thus 

 arises. One part of this bladder gradually sinks 

 inward, and its cells form a hollow, which be- 

 comes deeper and deeper, just as if a boy were 

 pressing his finger into a perforated rubber ball. 

 In this way the bladder becomes a cup, consist- 

 ing of two cells bent against one another and wide 

 open toward the center. The cells of the inner 

 wall become stomach cells, and those of the outer 

 wall skin cells, the opening of the gap is the" 

 mouth, and the Gastrula is complete. 



This process, I repeat, is typical throughout, 

 even in individuals, where the Gastrula itself is 

 no longer the end of the process. The play of 

 forces always begins with the disintegration of 

 the egg cell into many cells, which gradually 

 gather themselves into a lump like a mulberry. 

 The tendency to form a hollow cylinder, or blad- 

 der, always exists and the final end is always the, 

 formation of the genuine Gastrula stage, or of 

 its equivalent, that is to say, a double stratifica- 

 tion of the cells by a primitive arrangement of 

 the simple building material into two mem- 

 branes. 



If the biogenetic law has any meaning at all, 

 it is that at this extreme end of evolution it has 



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