180 THE STORY OF LIFE'S MECHANISM. 



changing its nature, and it thus continues to 

 grow, and is handed down from generation to 

 generation, always endowed with the power of 

 developing into a new individual under proper 

 conditions, and of course when it does thus give 

 rise to new individuals, they will all be alike. 

 We can thus easily understand why a child is like 

 its parent. It is not because the child can inherit 

 directly from its parent, but rather because both 

 child and parent have come from the unfolding 

 of two bits of the same germ plasm. This fact 

 of the transmission of the hereditary substance 

 from generation to generation is known as the 

 theory of the continuity of germ plasm. 



Such appears to be, at least in part, the ma- 

 chinery of heredity. This understanding makes 

 the germ substance perpetual and continuous, 

 and explains why successive generations are alike. 

 It does not explain, indeed, why an individual 

 inherits from its parents, but why it is like its 

 parents. While biologists are still in dispute 

 over many problems connected with heredity, 

 all are agreed to-day that this principle of the 

 continuity of the heredity substance must be the 

 basis of all attempts to understand the machinery 

 of heredity. But plainly this whole process is a 

 function of the cell machinery. While, there- 

 fore, the idea of the continuity of germ substance 

 greatly simplifies our problem, we must acknow- 

 ledge that once more we are thrown back upon 

 the mysteries of the cell. Until we can more 

 fully explain the cell machine we must recognize 

 our inability to solve the fundamental question 

 of why an individual is like its parents. 



