220 Life and Death, Heredity and Evolution 



and that it must take place in order that the lost vitality 

 shall be restored. But when we examine the evidence on 

 this in lower organisms, we find a whole series of facts that 

 will not range themselves under this doctrine, along with some 

 that will. After mating, some organisms are less vigorous 

 than before ; some little altered ; some more vigorous. The 

 latter may be held to show rejuvenescence. But the gen- 

 eral result is to produce many diverse stocks with new sets 

 of hereditary characters. Some of these new combinations 

 show greater vigor, others less ; and they differ in many 

 other ways. Such diverse stocks resulting from mating 

 show similarities among themselves, resulting from their de- 

 pendence on the union of two parents ; that is, they show 

 biparental inheritance. But the stocks produced by a given 

 mating differ, too, in their hereditary characters. 



These relations, as yet little known in the lower organisms, 

 receive illustration on a vast and conspicuous scale in the 

 higher organisms, where they are known as Mendelian in- 

 heritance. The offspring of a given pair are more alike 

 than are the offspring of diverse pairs. Nevertheless, the 

 offspring of a single pair show combinations of hereditary 

 characters diverse from each other and from their parents. 



Examining the minute processes that occur in reproduc- 

 tion from two parents, we find that there is a visible forma- 

 tion of new combinations of the chemicals on which develop- 

 ment and function depend; new combinations, of the pri- 

 mary hereditary characters. These chemicals are in vis- 

 ible packets, and the method of forming new combinations 

 of them can be seen under the microscope. Even when, as 

 often happens, the mating is between parts of the same 

 nucleus of the same cell, the processes are such as to bring 

 about new combinations of the primary hereditary sub- 

 stances ; organisms with new combinations of hereditary 



