60 STATISTICAL METHODS. 



Thus the first class has 6.25% purely dominant in both 

 characters; the second class, 12.5% purely dominant in one 

 character and hybrid in the other, and so on. Recalling that 

 hybrid zygotes produce somas with the dominant character, 

 it follows that the progeny appear as follows: 



Ratios 

 A. dom. + B. rec ........... 18.75% 3 



'A. rec. +B. dom .......... 18.75% 3 



A. dom. + 5. dom .......... 56.25% 9 



A. rec. +B. rec ........... 6.25% 1 



This result again agrees with experiment. The resulting 

 mixture of characters in tri- to poly hybrids may be likewise 

 predicted, by extending the principles already laid down. 



MEASURE OF DISSYMMETRY IN ORGANISMS. 



A Dissymmetry-Index, 3, measuring the average de- 

 gree of asymmetry in the right and left organs of bilateral 

 organisms, has been proposed by Duncker (1903). 



First a series of integral differences 3, 2, 1, 0, 1, 2, 

 3, 4, etc., between the right- and left-side measurements of 

 the organ in question is made, and the frequencies of each 

 integral difference (reckoning to the nearest integer) is found. 

 The average of the difference series is the difference of the 

 averages of the right- and left-side measurements, and the 

 standard deviation of the difference is given by 



in which the subscripts, refer to the bilateral series of which 

 the asymmetry is to be found, and r is the coefficient of cor- 

 relation between the two sides. 



Let d' represent any positive differences in the series, and 

 d" any negative differences; and let /,/, //, etc., represent 

 the frequencies of the negative-difference, classes, and //', 

 //', etc., the frequencies of the positive-difference classes. 

 Then the asymmetry-index 



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