44 



GENETICS 



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

 first instance the number of ribs fluctuates around 



Number oi 

 Individuals 



35 p. UsTor Constants 



30 



£5 



Arithmetical MeanCA.M)=49 

 Mode CM) -5 



Average Deviation (A.D.')=.5£ 

 Standard Deviation (o-) = .7e4 



— CoeKicient oi VariabilitY (C.V.)= 1^1 



Formulae 



zo - 



15 



W 



t 



A.D. = S(x.f) 



=T 



cr = rzcx^.f) 



- c.\/ = 



n 



A.M. 



2 = sum 



x= deviation of the class 

 from A.M. 



f = number in the class 

 n =• total number 



Number of Rays £ 3 4 5 



Fig. 25. — The fluctuating variability of starfish rays. 



Goldschmidt. 



6 7 



From data by 



eighteen as the commonest kind ; in the second case, 

 around fifteen. Such a difference could not easily 



