EARWIG -FORCEPS 



209 



These forceps are, in the case of the common earwig — and they 

 have not heen studied from this point of view in any other 

 species — remarkable, because of the great variation in their 

 development in the male, a character which again reminds us 

 of the horns of Lamellicorn beetles: in the female they are 

 comparatively invariable, as is also the 

 case in the few species of Lamellicornia, 

 which possess horned females. A and 

 B in Figure 109 represent the forceps 

 of different males of the common earwig, 

 C showing those of the other sex. The 

 subject of the variation of the male 

 callipers of the earwig has been con- 

 sidered by Messrs. Bateson and Brind- ^"^- ^°^- — ^°"^P? °\ '^^ 



'^ . common earwig : A, ot large 



ley,i who examined 1000 specimens male ; B, of small male ; 

 cajDtured on the same day on one of the ^' °^ f'^™''''°- 

 Fame islands off the coast of Northmnberland ; 583 of these were 

 mature males, and the pincers were found to vary in length 

 from about 2-^ mm. to 9 mm. (A and B in Fig. 109 repre- 

 sent two of the more extreme forms of this set of individuals.) 

 Specimens of medium size were not, as it might perhaps have 

 been expected they would be, the most common ; there were, 

 in fact, only about 12 individuals having the forceps of the 

 medium length — 4J to 5^ mm., while there were no less than 

 90 individuals having forceps of a length of about 7 mm., and 

 120 with a length of from 2^ to 3^. Males with a medium 

 large length of the organ and with a medium small length 

 thereof were the most abundant, so that a sort of dimorphism 

 was found to exist. Similar relations were detected in the 

 length of the horns of the male of a Lamellicorn beetle examined 

 by these gentlemen. In the case of the set of earwigs we have 

 mentioned, very little variation existed in the length of the 

 forceps in the female sex. 



In many earwigs — including F. auricularia — there may be 

 seen on each side of the dorsal aspect of the true fourth, or of the 

 fourth and neighbouring segments of the hind body a small 

 elevation, called by systematists a plica or fold, and on examina- 

 tion the fold will be found to possess a small orifice on its 

 posterior aspect. These folds are shown in Figs. 105 and 108 ; 



1 Froc. Zool. Soc. London, 1892, p. 586. 

 VOL. V P 



