176 THE STORY OF LIFE'S MECHANISM. 



tained potentially all the hereditary traits handed 

 down from parent to child, the chromosomes of 

 each daughter cell will contain similar hereditary 

 traits. If, therefore, the original fertilized egg 

 possessed the power of developing into an adult 

 like the parent, each of the daughter cells should 

 likewise possess the power of developing into a 

 similar adult. And thus each cell which arises as 

 the result of such division should possess similar 

 characters so long as this method of division con- 

 tinues. But after a little in the development of 

 the egg a differentiation among the daughter cells 

 arises. They begin to acquire different shapes 

 and different functions. This we can only believe 

 to be the result of a differentiation in their 

 chromatin material. In the cell division the 

 chromosomes no longer split into equivalent 

 halves, but some characters are portioned off to 

 some cells and others to other cells. Those cells 

 which are to carry on digestive functions when 

 they are formed receive chromatin material which 

 especially controls them in the performance of 

 this digestive function, while those which are to 

 produce sensory organs receive a different por- 

 tion of the chromatin material. Thus the adult 

 individual is built up as the cells receive different 

 portions of this hereditary substance contained in 

 the original chromosomes. The original chromo- 

 somes contained all hereditary characters, but as 

 development proceeds these are gradually por- 

 tioned out among the daughter cells until the 

 adult is formed. 



From this method of division it will be seen 

 that each cell of the adult does not contain all 



