38 



DISCONTINUOUS VARIATION. 



been collected at random in one day in the Fame 

 Islands. Only mature males with elytra fully devel- 

 oped were measured. The range of variation was from 

 2.5 to 9.0 mm., the various lengths occurring with a 

 frequency indicated by the accompanying curve. Here 



120 



100 



"3 

 I 80 



a 



M 



*M 



o 



60 



40 



SO 







4567 

 .Length o;f< Forceps in >mm. 



FIG. 7. Distribution of various lengths of forceps in the 



male earwig. 



we see that the commonest kinds had a length of either 

 3.5 mm., or 7 mm., or were of the forms shown in Fig. 

 8; whilst individuals of intermediate length occurred 

 comparatively infrequently. This species was there- 

 fore most distinctly dimorphic in respect of the char- 

 acter measured, and it maintained this dimorphism in 

 spite of the fact that the varying individuals were liv- 



