1895- SEXUAL SELECTION. 405 



concourse of atoms of colouring matter " without external (female) 

 sanction. I think it will be found that the harmonious distribution 

 of tints on the feather of the argus pheasant merely continues a 

 principle which the bilateral and radiate forms of all living organisms 

 illustrate — the coincidence of symmetry with economy ; and that, 

 although " likes and dislikes " will always exist, sexual selection, 

 from being an efficient cause, becomes an untimely dens ex mnchina like 

 so many others. 



So far the remarks have not been constructive, but one sugges- 

 tion, at least, of a positive nature may be gleaned from two facts in 

 the life-history of Lacerta muralis. 



The first of these is that, considering the number of enemies, 

 four-footed, winged, and creeping, that persecute this species, the 

 struggle for existence must obtain as severely here as with any other 

 animal. The second fact relates to the predominance of some 

 varieties over others, and becomes apparent if we trace their manner 

 of colour development. In the nigvivenivis form, for instance, we see 

 that the black is first visible in the shape of minute spots on the 

 throat, each scale being often prettily marked with a black centre. 

 The next stage consists in the entire under-surfaces being thus 

 covered with minute spots that afterwards, in the true var. nigviventris, 

 Bonap., expand to the exclusion of all other colouring. In localities 

 where this variety has become dominant, the first gradation of colour- 

 development has been abbreviated, and the young already display the 

 intermediate stage. The young and females are not so darkly tinted 

 as the males. 



From these circumstances we conclude that the parental stock 

 was less strongly pigmented, and also that the present scattered 

 nigriventris forms are not the discontinuous residue of a once all- 

 prevalent race, for, in that case, the young would have this feature 

 most pronounced. They must, therefore, have arisen spontaneously, 

 so to speak : independently of each other. Nor can their mutual 

 resemblance be explained by identity of external conditions, for this 

 form occurs sporadically on a variety of soils on different shores of 

 the Mediterranean and on some of its islets, as well as further north.. 



By what obscure selective process has this preeminently indijf event 

 character of black colouring on the lower surfaces been perpetuated 

 and intensified ? Considering our ignorance of the causes of variation 

 it would be rash to state that the whole polymorphic cycle of varieties 

 of this species are distinguished by equally non-adaptive characters, 

 but this certainly applies to some other recent forms like the 

 rubriventris, flaviventris, etc.,^ whose characteristic tints are of the 

 " useless " class. 



1 The phylogeny of these races is corroborative of the general rule that animal 

 beauty tends to increase, a fact that is sometimes attributed to " growing taste " on 

 the part of the female sex. The effects of sunlight (Eimer, " Organic Evolution," 

 p. 91) cannot explain brighter colouring on the lower surfaces of L. muralis. 



