loss of power by idleness, are processes which 

 may, and frequently do, extend through the 

 greater part of long lives. There is no known 

 limit to the increase of powers. The decrease 

 of powers is limited only by death. 



4. When the matter extends over two or 

 more generations, improvements come through 

 the offspring of old parents and not through the 

 offspring of young parents. This means that 

 the origin of improvements is to be found in 

 something which occurs in the lives of parents 

 between youth and old age, and not in some 

 spontaneous variation occurring in a germ. 



5. When the matter extends over two or more 

 generations, improvements in a particular form 

 of power, (as mental power, trotting power, 

 resistance to disease, etc.), come through the 

 offspring of parents who exercised that particu- 

 lar power to an unusual extent before reproduc- 

 ing, and not through the offspring of any other 

 kind of parents. 



6. When a man develops the muscular 

 strength of his arms and hands by manipulating 

 a pair of shears which he uses to cut off the tails 

 of mice, the effect produced upon the muscular 

 strength of the subsequently conceived son of this 



