OTHER THEORIES OF SEXUAL COLOURING 315 



Recognition between the sexes appears to be complete, 

 and infertile crossing does not occur even when 

 two species closely resemble each other 



To this it may be replied that pairing between the 

 individuals of distinct species is extremely rare, and 

 does not seem to be any commoner among species in 

 which this means of recognition would lead to failure. 

 If the resemblance between the white variety of the 

 female Clouded Yellow (Colias edusa, var. helice) and 

 the female Pale Clouded Yellow (Colias hyale) does not 

 lead to infertile pairing ; if the practical identity of 

 the Sallow and Poplar Kittens (Cerurafurcula and C. 

 bifida), of the Swallow Prominent and Lesser Swallow 

 Prominent {Leiocampa dictcea and L. dictceoides) , of 

 the Common and Dark Dagger Moths {Acronycta psi 

 and A. tridens), does not lead to dangers of the kind, 

 we must conclude that wide differences of colour and 

 pattern cannot have been produced by a gradually 

 lessening number of infertile crosses. 



In the case of mimetic species, it is a comparatively 

 common thing for the female of one species to be 

 chased by the male of another, and yet, in spite of a 

 wonderful superficial resemblance between the females, 

 it is very improbable that the courtship proceeds 

 beyond its most preliminary stages. The same is true 

 of the Clouded Yellows referred to above, and of 

 Clouded Yellows and Common Whites. These, and 

 many other examples of the kind show that this means 



