CHARACTERS OF NAUSEOUS GROUPS 279 



groups should be far more alike than those of others, why 

 they should resemble members of other such groups in 

 the same region, why they should have conspicuous 

 patterns and contrasted colours which in Lepidoptera 

 tend to be the same upon the under as on the upper side 

 of the wings, why their flight should be slow and flaunt- 

 ing, why they should be remarkably tenacious of life. 

 Here are a number of important characters associated 

 together, and true of all such groups wherever they may 

 occur in any part of the world. One theory alone explains 

 all the numerous observations which are here condensed 

 into a brief statement. It is by no means an assumption 

 to maintain that the groups in question are specially 

 defended. This is admitted to be the case with the 

 Hymenoptera, and there is now a very large mass of 

 experimental evidence in the Lepidoptera. 1 



Another admitted fact of wide application is the ten- 

 dency of Mimetic Resemblance to appear in the female 

 rather than the male. Thus mimetic female butterflies of 

 many species are associated with non-mimetic males, while 

 the converse relationship is almost unknown. Such non- 

 mimetic males maintain the ancestral appearance which 

 has been lost in the mimetic females. It is interesting to 

 observe, however, that more or less distinct traces of the 

 original pattern can generally be recovered by the careful 

 study of individual variation in the females. This is 

 a remarkable reversal of the ordinary rule that when male 

 and female differ the latter is the more ancestral. This 

 striking exception is quite unintelligible except under the 

 theory of Natural Selection, which offers the convincing 

 explanation, long ago suggested by Alfred Russel Wallace, 

 that the slower flight of the heavier females and their 

 exposure to attack during oviposition render it especially 

 advantageous for them to resemble conspicuous distaste- 

 ful species in the same locality. 2 



Another aspect of Mimicry affords, in my opinion, 



1 See especially Frank Finn in Journ. Asia/. Soc. Bengal, lxiv, pt. ii, 

 l8 95. P- 344 5 Ixv, pt. ii, 1896, p. 42; lxvi, pt. ii, 1897, p. 528, and 

 p. 613. 



2 Trans. Linn. Soc. Lond., vol. xxv, 1866, p. 22. 



