well, are likely to be revealed. The following problems at 

 first sight suggest certain correlations which may be far 

 from the truth: 



(1) What is the correlation between length and weight 



in ears of corn? 



(2) Between white cats and deafness? 



(3) Between black pigs and cholera? 



Yule 's formula is generally used in problems of correla- 

 tion involving presence or absence but not degree, as in 

 problems (2) and (3) above. M and N are the characters, 



ad— be 



ad+bc 



When the characters are present in varying degree as 

 in problem (1) above, another formula is employed: — 

 £DlDw 



r = — 



n Sl Sw 



Dl = deviation from mean length (or size etc.) of ears. 

 Dw = deviation from mean weight of ears. 

 Sl = standard deviation of length of ears. 

 Sw = standard deviation of weight of ears. 



(See Davenport, Principles oj Breeding). 



Chapter 9— THE TRANSMISSION OF CHARACTERS 



(a)— Darwin's Theory of Pangenesis (1869) 



Several theories have been proposed to account for the 

 transmission of modifications Darwin, in his Variation of 

 Animals and Plants under Domestication, suggested that 

 very minute particles, called gemmules, are given off 

 from\all the cells of the body, which multiply by fission, and 

 are ultimately carried to and aggregated in the germ cells 

 In development the gemmules unite with others like them- 

 selves, and grow into cells like those from which they were 

 originally given off. This theory has been shown untenable 

 by Galton and others; besides it is based on the erroneous 

 idea that the body makes the germ cells. 



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