THEORIES OF HEREDITY 69 



been found. Weismann says amphimixis serves as a 

 means for the co-mingling of two separate hereditary 

 tendencies, and is, therefore, a source of variation. O. Hert- 

 wig and others, on the contrary, have maintained the 

 opposite view, holding that its effect is to prevent varia- 

 tion. Delage thinks there is something to be said for both 

 sides. As in the act of fertilization two ancestral strains 

 are mixed, it is evident that this makes it possible for the 

 child to resemble two lines of ancestors instead of one. On 

 the other hand, any odd individual peculiarities are likely 

 to be swamped by the addition of another germ-plasm 

 which does not contain them, as will be seen presently. 



A MIXING OF PARENTAL QUALITIES. 



We have already seen that the germ-cells of the same 

 parent are not all identical, but become, by means of the 

 reducing division, individually different from each other. 

 We know, further, that in the process of fertilization two 

 such germs unite to form the new individual, which thus 

 has a double inheritance paternal and maternal. How 

 does this double set of qualities, derived from the two 

 parents, behave in its ensemble, or, in other words, in what 

 way is the constitution of the offspring determined by the 

 mixing of the constituent qualities of the parents ? Accord- 

 ing to the role and predominance of either of the parental 

 characteristics, we can distinguish three types of in- 

 heritance : 



(a) Blended Inheritance, where the offspring in its 

 characteristics forms an average between both parents ; 



(b) Exclusive or Prepotent Inheritance, where the off- 

 spring follows predominantly one parent ; 



(c) Particulate Inheritance, where the offspring follows 

 in some details of its characteristics the one parent, in other 

 details the other parent. 



For the sake of greater clearness, we shall first deal with 

 the inheritance of racial traits, as exemplified in the 



