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POPULAR SCIENCE MONTHLY. 



simply suppose that each parentage produces one couplet of grown-up 

 filials, an adult man and an adult woman. 



The result is shown to the nearest whole per thousand in the diagram 

 up to 'U and above/ It may be read either as applying to fathers and 

 their sons when adult, or to mothers and their daughters when adult, 

 or, again, to parentages and filial couplets. I will not now attempt to 

 explain the details of the calculation to those to whom these methods 



are new. Those who are familiar with them will easily understand the 

 exact process from what follows. There are three points of reference 

 in a scheme of descent which may be respectively named 'mid-parental,' 

 'genetic' and 'filial' centers. In the present case of both parents being 

 alike, the position of the mid-parental center is identical with that of 

 either parent separately. The position of the filial center is that from 

 which the children disperse. The genetic center occupies the same posi- 

 tion in the parental series that the filial center does in the filial series. 

 'Natural Inheritance' contains abundant proof, both observational and 



