OF WASHINGTON. 87 



that the failure of any of the wingless earwigs to lose the forceps 

 is not in accord with commonly accepted evolutionary theories. 

 Instead of dropping the forceps with the wings, the caudal ap 

 pendages have, in some cases, apparently increased in size, and 

 have certainly continued to differentiate in form, attaining, for 

 example, a marked asymmetry in the wingless genus Anisolabis, 

 a condition which could not possibly have a functional signifi 

 cance in connection with the wings, and in all probability has 

 none in any other relation. The continued presence of the for 

 ceps in the wingless earwigs is, moreover, paralleled as an evolu 

 tionary phenomenon by the equally useless multiplicity of form 

 which appears in the forceps of the winged genera. The func 

 tion here ascribed to the organs in question renders it highly im 

 probable that there is the slightest use in the differences of form, 

 size, and armature of the forceps, and the great variability of 

 these characters also forbids the supposition that any definitely 

 specialized uses remain unknown. Both sexes of Labia minor 

 use their forceps in the same manner, though the form of the ap 

 paratus is very different, and it is nearly twice as long in the male 

 as in the female. This is probably one of the endlessly numerous 

 secondary sexual differences having no direct use, but perhaps 

 serving an important purpose in contributing to the diversity 

 which many organisms maintain inside specific lines. The gen 

 eral maintenance of a direct proportion between the length of 

 the abdomen and the length of the forceps* supports the view 

 that natural selection has tended merely to keep the forceps long 

 enough to reach back to the wings. 



The field of biology abounds, however, in similar phenomena 

 which appear to be anomalous and mysterious when viewed from 

 exclusively selectional or static theories of evolution, but which it 

 seems preferable to interpret as examples of a general law of bio 

 logical change for its own sake, as it were, and independent of 

 natural selection.! 



As accessories of the organs of flight the forceps are, of course, 

 to be looked upon as an adaptation, but from what? Presumably 

 from the jointed stylets to be found in so many groups, but more 

 particularly from such as those of the peculiar insect described 

 by Westwood, under the name Dyscritina^ but subsequently re 

 ported to be the larva of an earwig. Dyscritina, which the 

 writer has observed and collected in Liberia, may be said to com- 



* In a few cases where slender species have short forceps, the abdomen 

 seems to be unusually flexible, but in general the long forceps go with the 

 long bodies. 



t A. Kinetic Theory of Evolution, Science, N. S., XIII. No. 338, 

 pp. 969-978, June 21, 1901. 



% Trans. Ent. Soc. London, 1881, p. 601. PI. xxii, Figs.l-li. 



