THE THEORY OF MIMICRY 155 



utility, the action of natural selection might be of use in 

 expediting the process by the (elimination of those that 

 showed a disposition to reversion or to stagnation. The 

 doctrine of natural selection assumes that no variation 

 can maintain itself unless it serves a useful purpose in 

 the struggle for existence. 



Sexual selection suggests the acquirement of adorn- 

 ments for the purpose of displav by the male sex in order 

 to attract the otlier sex. It, therefore, only benefits the 

 individual in rivahy with others of his kind, and more 

 often than not, from the nature and even monstrosity 

 of the developments, it must handicap rather than aid 

 him in his usual avocations. Under Sexual Selection 

 are included such strange and bizarre devices as the 

 ch'peal and tboracic horns of some Lamellicorn beetles; 

 the monstrous developments of the posterior legs of Hop- 

 liniP and Sagrina\ the tails of some Lepidoptera and a 

 thousand and one other examples that might be cited 

 among insects, in which abnormal appendages occur, to 

 which no beneficial use can be assigned other than that 

 of adornment. Among the vertebrates and other orders 

 numerous examples occur of a similar nature. 



In addition to those cases which can be attributed to 

 sexual selection, there are many others in which abnor- 

 malities are common to both sexes, and which certainly 

 cannot be accounted for under that of Natural Selection. 

 As examples: — The Craneflies (Tipulida:^), wath inordi- 

 nately long weakly-jointed legs; Membracidae (sub-family 

 Centrotimie), with extraordinary thoracic appendages; 

 the genus Mormolyce (Carabid^e), from the East Indian 

 islands, long-tailed Lepidoptera, such as Dianeura sp., 

 of East and North-East Africa, the hind Avings of which 

 have been modified into caudal processes or balances, and 

 which, by the way. are strongly analogous to similar ap- 

 pendages borne by the Nemopterinae (Neuroptera). From 

 what I have written above it will be inferred that I am 

 strongly inclined to doubt whether natural selection has 

 more than a very subsidiary role in the production of 



