PROTECTIVE MIMICRY. 21 5 



common Whites, Clouded Yellows, Brimstone, etc)., is totally 

 different from the Heliconidte, not only in colour but in the 

 shape of the wings ; the Wood White, however (Leucophasia, 

 xn/apis), presents a certain likeness to the Heliconidre in the 

 shape of the wings, and also in the comparative feebleness of 

 its flight a circumstance which will perhaps cause its extinc- 

 tion in the future. The feeble flight is perhaps a necessary 

 concomitant of the shape of the wings ; it is not at all needful 

 to believe the suggestion has been made that the genus 

 Lt'jrfalis imitates the Heliconidse in its wretched powers of 

 flight as well as in the form of the wings and their markings ; 

 it is much more likely the insect is a poor flyer on account of 

 the shape of its wings, and that this very circumstance rendered 

 the mimicry necessary as an alternative to extinction. But, 

 even starting with a form like the Wood White, there is a 

 very considerable distance to be traversed before the Leptalis 

 becomes at all like an It/wmia. 



This difficulty has been met by Fritz Mliller * ; a com- 

 parative study of a number of different species of Leptalis led 

 him to believe that the banded forms are the most archaic ; 

 comparatively little modification, therefore, was needed to pro- 

 duce the detailed resemblance between the several species of 

 Leptalis and the protected Mechanitis and Acrcea. 



If this is generally the case, it is far easier to believe in the 

 efficiency of natural selection in bringing about mimicry ; but 

 it raises the further question How are we to account for the 

 initial likeness ? The answer to this question may bring us 

 back to the neighbourhood of the theory of ''like conditions" 

 to the view expounded by Murray, and the earlier opinion of 

 Mr. Wallace. 



* Jettaische Ztitschrift, 1870. This important paper is noticed in the 

 American Naturalist for 1876, p. 535. 



