278 



THE ENTOMOLOGIST. 



hypothesis, that if a male with four spots paired with a female 

 with nine, the offspring would have (^ x 4) + (|^ x 9) = 65^ spots 

 each ; but this is not intended, as it is contrary to observation, 

 and also to theory, since, if the different aberrant individuals 

 bred true, they would constitute varieties, and this is not the 

 case. What the hypothesis does maintain is that 6|- spots repre- 

 sent the average number of spots distributed more or less un- 

 equally among the offspring, i.e. it is the " spot-power" trans- 

 mitted to the offspring. This may appear fanciful, but it must 

 be remembered that it is symbolical of an established proba- 

 bility, and also that we are dealing with only one factor in 

 heredity. 



Now, I want to find the mean "spot-power" of all the indi- 

 viduals mentioned in Table I. This I do by drawing a Scheme 

 of Distribution, utilizing for this purpose the columns 1 and 3 in 

 Table I. By this means curve A of tig. I. is obtained. 



Fig. I. 



Note. — The lines for construction of curve B have been rubbed out, 

 but they may be filled in again according to the explanation in the 

 note at the end. 



Curve A gives 4|- as the mean " spot-power." 

 Now, I want to find out what would be the mean " spot- 

 power " of the next generation if all the individuals of Table I. 

 paired and produced offspring. The same percentages may be 

 taken, as it is supposed that each pair produced an equal number 

 of offspring ; the only difference between the values in column 3, 



