THEORIES OF HEREDITY 83 



grandparent works out in these cases somewhat differently. 

 As the image * of the individual is always the outcome of 

 the union of two parental strains, the possibility is rarely 

 given that a child may completely resemble one of its 

 parents or grandparents, for in each case the image of the 

 individual is determined by the paternal plus maternal 

 germ-plasms. In order that a child may exclusively repeat 

 the image, be it of its father or of its grandfather, we would 

 have to assume that each time the maternal Idants which 

 enter into combination with the paternal Idants are in their 

 effect completely suppressed, which is hardly likely to occur 

 in a series of generations. There- _ 

 fore, that the grandchild may ex- /X 

 clusively resemble one grandparent 

 e.g., its grandmother it is neces- ^ 



sary that exclusive inheritance take ' "" 



f^i*"" 



S(D) 



place successively in grandmother, & i D \ p\ 

 father, and child. For if we assume /"\ \ D / L/ 

 A and B (see Fig. 43) to be the v s 



Idants of the two grandparents ^^/ 



(first generation), then the father 

 (second generation) has the germinal 

 constitution AB, where we must 

 assume A to be predominant over FIG. 43. ATAVISM. 

 B, so that the father resembles the 



grandfather A only, while the characteristics of the grand- 

 mother B are latent and do not come to expression. 

 Some of the father's germ-cells, which contain half the 

 number of his Idants, will contain only the Idants B. 

 These, in combination with Idants D from the mother, 

 will represent the grandchild (third generation). But, in 

 order that the grandchild may exclusively resemble its 

 grandmother B, the Idants B derived from the father will 

 have to be predominant over the Idants D derived from the 

 mother, as the Idants B must also have been the dominant 



* Image here denotes the sum total of the characters expressing 

 the individuality of each single being (Weismann). 



