IV] HEREDITY 39 



slope is measured by the size of the angle EOC. The 

 angle made by the diagonal at is 45°, the tangent 

 of which is 1 (unity). If there were no correlation 

 the angle would vanish, EF coinciding with CD, and 

 the correlation coefficient would be 0. Intermediates 

 are represented by the value of the tangent of the 

 angle EOC. In practice it rarely happens that the 

 points representing the means of the sons for each 

 class of fathers lie in a perfectly straight line ; when 

 they approach it closely the correlation is called 

 'linear'; when they depart from it considerably, it 

 is called ' skew.' 



Table of intensity of parental inheritance in different 

 species. (From Pearson.) 









Number 







Mean 



of Pairs 



Species 



Character 



value 



used 



Man 



Stature 



•506 



4886 





Span 



•459 



4873 





Forearm 



•418 



4866 





Eye Colour 



•495 



4000 



Horse 



Coat Colour 



•522 



4350 



Basset Hound 



Coat Colour 



•524 



823 



Greyhound 



Coat Colour 



•507 



9279 



Aphis 



Ratio of right Antenna 



•439 



368 



(Hyalopterus 



to Frontal Breadth 







trirhodus) 



(non-sexual reproduction) 







Water- flea 



Ratio of Basal Joint of 



•466 



96 



{Baplinia magna) 



Antenna to Body length 







(non-sexual reproduction) 



