n] 



VARIATION 



17 



variation hitherto considered. It is possible that 

 dimorphic cases in which intermediates exist are 

 really essentially discontinuous, but that the two 

 groups into which the species is divided each exhibit 

 continuous variation about the mode for the group, 

 to such an extent tliat the higher members of one 



140 



ISO 



120 



110 



100 



90 



80 



70 



60 



50 



40 



30 



20 



10 



Lengths of Forceps in Millimetres 



Fig. 5. Curve with two modes, representing frequency of lengths 

 of forceps of male Earwigs from the Fame Islands. (After 

 Bateson.) 



group overlap the lower of the other. For example, 

 if the modal (most frequent) stature for a race of 

 men were 68 inches, and for the women 62 inches, it 

 might happen that on plotting a frequency curve for 

 the stature of adults including both sexes, a curve 

 D. 2 



