156 Heredity. 



ii. 



Whenever, then, the strict conditions of intermixture are wanting, 

 the rule is that one of the parents is preponderant When we 

 study empirically the laws of heredity, we find that this case is of 

 by far the most frequent occurrence. Common language translates 

 this everyday experience into such phrases as these: this child 

 reminds one of his father ; or, that child is the image of its mother. 

 But experience also teaches us that this preponderance takes place 

 in two ways, being sometimes direct, sometimes diagonal. 



Sometimes the preponderance is manifested in an individual 

 of the one sex on the child of the same sex ; in that case the son 

 resembles the father ; the daughter the mother. 



Again, this preponderance is manifested in the opposite sex; 

 then the daughter resembles the father, and the son the mother. 



We will consider the latter case first 



When we study heredity empirically, when, that is, we observe 

 facts and the generalizations which immediately result from it, the 

 formula which includes the largest number of facts and admits of 

 the fewest exceptions is the following : Heredity passes from one 

 sex to the opposite. This assertion may at first appear strange, 

 and even' entirely at variance with what has already been said, 

 that like produces like. This will hereafter be explained ; but 

 perhaps it will appear less difficult of comprehension if we follow 

 heredity through several generations. It will then be seen to pass 

 from the grandfather to the mother, and then from the mother to 

 the son; or from the grandmother to the father, and from the 

 father to the daughter. Thus it returns to its starting-point 



But not to dwell on this question here, we would remark that 

 the thesis of cross heredity is admitted by several great physio- 

 logists, such as Haller, Burdach, Girou de Buzareingues, and 

 Richerand. ' This explains,' says the latter, ' why so many great 

 men have mediocre sons.' Michelet thinks that history justifies 

 him in broadly affirming the existence of cross heredity. ' No 

 other king,' says he, speaking of Louis XVL, 'exemplifies better 

 a law of which history has but few exceptions. The king was a 

 foreigner. Every son takes after his mother. The king was the 



son of a foreign woman, and had her blood. Succession in such 



ft 



