44 



GENETICS 



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

 first instance the number of ribs fluctuates around 



of 



individuals 



55 



/5 



10 



LIST or CONSTANTS 



Arithmetical Mean(A.M)=49 

 Mode CM) -5 

 Average Deviation (A.D.)=.5 

 Standard Deviation (cr) = j4 

 Coefficient of Variability (C.V> \.-ri 



FORMULAE 

 A.D. = 2(x.f) 



x- deviation of the class 



from A.M. 



f -number in the class 

 n -total number 



Number of Rays 3 4 5 6 7 



Fia. 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 



