VARIATION IN THE DERMAPTERA. 213 



Variation in tlie Dermaptera. 



By MALCOLM BURR, D.Sc, F.E.S. 



Variation in the Dermaptera is strongly marked, and of great 

 importance even from the purely systematic point of view, since 

 several forms of this phenomenon which run almost throughout the 

 group, have the effect of altering greatly the superficial appearance of 

 the creatures, and so have caused an excessive multiplication of so- 

 called species. 



It is most necessary for the student to grasp the principle forms of 

 variation in the Dermaptera, so that he may recognize the phenomenon 

 when he sees it, and thus avoid the error of regarding as a new species 

 what is nothing more nor less than a well-known form of polymorphism. 



Variation in Dermaptera may be in colour above, or in the actual 

 morphology. 



I., Variation in Morphology. 



Two kinds of morphological variation occur so persistently through 

 the Dermaptera that they afford regular cases of dimorphism : these 

 are brachypterism and macrolabiism. 



A. Brachypterism. 



This striking phenomenon, which earwigs share with the true 

 Orthoptera, with the Rhynchota, and doubtless with other insects, is 

 very general in the Dermaptera. Most known fully-winged species 

 are frequently brachypterous and indeed when the rarer forms are 

 better known, it is quite possible, if not even probable, that this kind 

 of dimorphism will be found to run throughout the order. 



When the organs of flight are in repose the wings are almost en- 

 tirely concealed by the elytra, only the chitinous squamje or wing- 

 scales projecting beyond them ; as these are frequently highly coloured, 

 it is evident that their absence must materially alter the appearance of 

 the creature, but even when shortened, they may be usually found by 

 lifting the elytra and looking beneath them. 



These dimorphic forms are often given the rank of varieties, and 

 we frequently find the expression " var. loufiipemm" " var. breiipennia," 

 " var. iiiacroptera," and " var. brachi/ptera " ; it is not really necessary 

 to dignify them with special names, if it is borne in mind that niacrop- 

 terous and brachypterous forms occur probably in all fully-winged 

 species. It is fairly safe to assume that the inacropterous form is the 

 normal one, and brachypterism the deviation. 



But it is important to remember that in brachypterous forms, the 

 elytra too, are often involved, being somewhat shortened and truncate; 

 for instance, To)noj)yiiia abjionuis, Borm., from Java, was for about 

 thirty years known only from the unique type in the Vienna Museum, 

 a brachypterous male, with decidedly short elytra, which was almost 

 treated as a generic character. But Mr. Jacobson found several females 

 at Samarang, all of macropterous form, with the elytra twice as long 

 as in the type and the wing-scales protruding prominently ; these 

 narrowly escaped being described as a new sjiiecii'Sj^jind for a moment 

 they appeared to require a new genus, fjo difitiient w^?fl||gi^;appearance. 



October 15th, 1914. /''^''^"' 'V\ 



^ MAY 8 19X5 ) 



