230 MENDELISM 
number of determinations of parental correlation 
have, however, since been made in the case of al] 
kinds of characters. The values show considerable 
variation, but the average which they indicate is much 
nearer to o°5 than to 0°33. Pearson therefore con- 
cluded that in none of these cases could anything 
resembling Mendelian inheritance be taking place, 
and that the latter is, in fact, the exception rather than 
the rule. 
Mendelians, aware of the certainty of their own 
results, and being convinced that these facts must 
have a very wide application, were thereupon driven 
reluctantly to the conclusion that something was 
seriously wrong with the methods adopted by biome- 
tricians for determining the coefficients of correlation. 
It seems, however, that this conclusion may have been 
arrived at with undue haste. 
In August, 1906, Mr. Yule read before the Inter- 
national Congress of Hybridization assembled in 
London a very interesting paper on ‘ The Theory of 
Inheritance of Quantitative Compound Characters on 
the basis of Mendel’s Laws.’ Though some difficulty 
was then experienced in following his argument by 
an audience unaccustomed to statistical methods, 
Yule’s conclusion is really very simple. 
Yule points out that the only character dealt with 
in Pearson’s memoir is the number of protogenic or 
allogenic couplets present in the individual, and it is the 
proportionate number of these couplets present in the 
parent and in the offspring respectively which is taken 
as determining the value of the correlation coefficient. 
