The Laws of Heredity. 



had vanished. Still these facts, however numerous and varied they 

 may be, may all be brought within the compass of a few formulas, 

 which might be called the empirical laws of heredity. These real 

 laws, which are so many aspects or incomplete expressions of the 

 ideal law, are the following, so far as observation reveals them. 



1. Direct heredity, which consists in the transmission of paternal 

 and maternal qualities to the children. This form of heredity 

 offers two aspects : 



(i.) The child takes after father and mother equally as regards 

 both physical and moral characters, a case, strictly speaking, of 

 very rare occurrence, for the very ideal of the law would then be 

 realized. 



Or (2), the child, while taking after both parents, more specially 

 resembles one of them; and here again we must distinguish 

 between two cases. 



a. The first of these is when the heredity takes place in the same 

 sex from father to son, from mother to daughter. 



ft. The other, which occurs more frequently, is where heredity 

 occurs between different sexes from father to daughter, from 

 mother to son. 



2. Reversional Heredity, or atavism, consists in the reproduc- 

 tion in the descendants of the moral or physical qualities of their 

 ancestors. It occurs frequently between grandfather and grand- 

 son, grandmother and granddaughter. 



3. Collateral, or indirect heredity, which is of rarer occurrence 

 than the foregoing, subsists, as indicated by its name, between 

 individuals and their ancestors in the indirect line uncle, or 

 grand-uncle and nephew, aunt and niece. 



4. Finally, to complete the classification, we must mention the 

 heredity of influence, very rare from the physiological point of 

 view, and of which probably no single instance is proved in the 

 moral order. It consists in the reproduction in the children by a 

 second marriage of some peculiarity belonging to a former spouse. 



Such are the various formulas under which all the facts of 

 heredity may be classed. We propose to study them in succession. 

 When to this we have added, as the necessary complement, the 

 study of the exceptions to these laws, we shall have passed in 

 review every single case of heredity. 



