44 



GENETICS 



either tree is unlike that of the other tree. In the 

 first instance the number of ribs fluctuates around 



Number of 

 Individuals 



35 



ZO 



15 



10 



LIST or CONSTANTS 



Arithmetical Mean (A.M)= 4.9 ^ 

 Mode CM) = 5 

 Average Deviation (A.D.)=.5 

 Standard Deviation (0-)= .846 

 Coefficient of Variability (C.V> 1 .72, 



FORMULAE: 

 A.D. = 



- C.V= ATFr 



Ssum 



x- deviation of the class 

 from A.M. 



f - number in the class 

 n- total number 



Number of Rays 3 4 5" 6 7 



FIG. 25. The fluctuating variability of starfish rays. From data by 

 Goldschmidt. 



eighteen as the commonest kind ; in the second case, 

 around fifteen. Such a difference could not easily 



