INTRODUCTION". 



chitmoiig processes, rooted into the last abdominal segment, which 

 IS enlarged in order to accommodate the powerful muscles whieli 

 work these organs. The forceps present a great diversity of 

 form : they may be remote or contiguous at the base ; thev may 

 be long and slender, or stout and conical ; they may have a round 

 or a trigonal cross-section ; they are invariably more or less 

 attenuate towards the apex and almost always slightly hooked at 

 the points themselves ; they may be strongly depressed and dilated 

 near the base (Forficuln), or slender and almost cylindrical 

 (Kos77ietor), or conical (Fsalis), very elongate (EudoJirnia), arcuate 

 {Pterygida), asymmetrically bowed (Anisolabis, BoreUia), undulate 

 m a vertical plane {Anechum, AUodaJiIia), armed with diversified 

 teeth {E2X(n'hits)- in both sexes of Apachyus they are curved, 

 siclde-shaped_ hooks. In the female they are almost invariably 

 simpler than in the male, being as a rule straight and unarmed'; 

 but in certain species of the CheUsocJihue the female has forceps as 

 highly organized as those of the male, though very different from 

 them, so that they have sometimes been described as male specimens. 



As a rule a given type of forceps will be found to characterize 

 a group of species, a genus, or a group of genera, but it is far from 

 rare to find very different forceps in closely allied species. The 

 forceps vary in different degrees within certain limits, aud a very 

 slight actual difference will often alter the superficial appearance 

 of a specimen to a remarkable extent. Care must be taken in 

 drawing deductions from the form of the forceps ; the remarks 

 upon these organs under the heading "Variation" should be 

 studied. The development of the forceps presents phenomena of 

 great interest which throw light upon the phylogeny of the 

 Dermaptera; these are referred to in the article upon the 

 development of Dijilat'/s. 



The forceps are subject to malformations due to wounds and 

 mutilations, and also to deficient nourishment. It is common 

 to find a male earwig in which one branch of the forceps is 

 formed as in the female ; such cases are frequently recorded as 

 hermaphrodites, but whenever the full complement of nine seg- 

 ments occurs together with one male branch, it is more probable 

 that these are not gynandromorphic specimens, but merely that 

 one branch has been unable to attain full development. Since 

 the specialization (armature &c.) of the forceps is purely a sexual 

 character, it is probable that the simple forceps of the female 

 represent the more primitive form, to which there would be a 

 natural tendency to revert. 



Cases undoubtedly due to traumatism are shown where an 

 immature specimen has one branch of the forceps pronged : this 

 is evidently caused by an attempt at reproduction of lost parts 

 caused by an injury to the immature forceps. Cases where the 

 forceps have the full complement of teeth but are misshapen or 

 distorted are probably caused by an injury received when the 

 insect has freshly emerged from the nymphal skin and is conse- 

 quently soft and tendei-. 



