98 NATURAL INHERITANCE. [CHAP. 



afterwards substituted, because the data seemed to 

 admit of that interpretation also, in which case the 

 fraction of two-thirds was preferable as being the more 

 simple expression. I am now inclined to think the 

 latter may be a trifle too small, but it is not worth 

 while to make alterations until a new, larger, and more 

 accurate series of observations can be discussed, and the 

 whole work revised. The present doubt only ranges 

 between nine-fifteenths in the first case and ten- 

 fifteenths in the second. 



This value of two-thirds will therefore be accepted as 

 the amount of Eegression, on the average of many 

 cases, from the Mid-Parental to the Mid-Filial stature, 

 whatever the Mid-Parental stature may be. 



As the two Parents contribute equally, the contribu- 

 tion of either of them can be only one half of that 

 of the two jointly ; in other words, only one half of that 

 of the Mid-Parent. Therefore the average Eegression 

 from the Parental to the Mid-Filial Stature must be the 

 one half of two-thirds, or one-third. I am unable to 

 test this conclusion in a satisfactory manner by direct 

 observation. The data are barely numerous enough for 

 dealing even with questions referring to Mid-Parentages ; 

 they are quite insufficient to deal with those that involve 

 the additional large uncertainty introduced owing to an 

 ignorance of the Stature of one of the parents. I have 

 entered the Uni-Parental and the Filial data on a 

 MS. chart, each in its appropriate place, but they are 

 too scattered and irregular to make it useful to give 



