214 THE entomologist's rkcord. 



The species being so long known only in the brachj^pterous state, it is 

 natural at first glance to look upon these macropterous individuals as 

 varieties or aberrations ; it will be interesting to see which form is 

 actual)}^ the commoner. 



Another instance is that of Sponr/ovostox kristenseni, Burr, from 

 Abyssinia. Mr. Kristensen sent over a large series, in which both 

 forms in both sexes were well represented ; the difference in appearance 

 was heightened by a simultaneous colour variation, but the fortunate 

 possession of a long series from one locality made it evident that it was 

 merely another instance of what might be called pterodimorphism. 



A further interesting example is afforded by the common earwig, 

 Fnrfirnla aaricularia, Linn., the macropterous form of which is 

 exceedingly abundant in Europe ; but a brachypterous form however 

 exists, which is very rare ; as the elytra are shortened also, and by 

 correlation the pronotum is somewhat broadened, this has been 

 described as a distinct species by Targioni-Tozzetti [F. silana, Targ.), 

 and by Brunner (7''. tarf/ioiiii, Br.), but the only so-called specific 

 characters are the abbreviation of the wings, slight shortening of the 

 elytra, and widening of the pronotum, which is a frequent correlative 

 with brachypterism : the noteworthy point in this connection is that 

 while the normal macropterous F. aaricularia is abundant throughout 

 Europe, the brachypterous F. ailana is confined to Italy, so far as we 

 know, with the rather surprising exception of a couple of females 

 recorded from the Isle of Wight. 



Instances of the description of the brachypterous and macropterous 

 forms of one and the same species, as totally distinct forms, even 

 placed in different genera, are by no means rare : thus For/inda 

 viiranda of de Bormans is the normal macropterous form of his Labia 

 acideata, the species being now assigned to the genus Nesuf/aster. 



Some species are still only known in one of the two forms, thus 

 F. Inrida, Pisch., L. snryrnensis, Serv., and many others, are only known 

 in the macropterous form, whereas F. piibescenx, Gene, F . lesni, Finot, 

 F. decipiens, Gene and many others only in the brachypterous ; prob- 

 ably F . decipiens, Gene, and F. Inrida, Finot, are a pair forming one 

 species, as in the cases of F. silana and F. aiiricularia ; in F. rudziankoi, 

 Sem., and F. sene(iale)if<is, Serv., both forms occur. 



The variation in the shape of the pronotum (where not sexual as in 

 the Diplatj/iiiae) is really correlative with brachypterism; it is very 

 usual in macropterous forms to find the pronotum more or less 

 widened posteriorly, apparently to accommodate the muscles which 

 work the wings; but when in the same species the wings are reduced, 

 the pronotum is correspondingly reduced by being narrower posteriorly 

 and so parallel-sided, as in JSlarava irallacci, Eahn., and many other 

 Labiidae, or by being shorter and broader, as in F. silana. 



In the two forms of Tomopygia abnorinis, Borm., however, the 

 pronotum is very small and narrow and in the very plastic highly 

 polymorphic Labidura riparia, Pall., the difference between the two 

 shapes of the pronotum is very marked. 



It is worthy of mention that in the Chelisoc/iidae, in which group 

 this dimorphism is less marked than in many others, the usual form 

 of the pronotum is rather long, and distinctly widened posteriorly, and 

 in this family, macropterism is the rule. 



