19 



Another species of Leuceronia, L. thalaasnia, has a.lso several 

 kinds of female, thoagh not so manj^ as L. ar<iia. Each of these 

 also resemhles a species belonging to one or other genus not at all 

 closely related to Leuceronia. 



I ought here to mention that though in speaking of these females 

 of Leuceionia I have given the name of the butterfly which each 

 form on the Avhole most resembles, it would in many instances have 

 been easy to adduce other species to which the resemblance is almost 

 equally close. The fact is that these homoeochromatic assemblages, 

 as they have been called, that is to say associations characterised by 

 similarity of colour and pattern, are often very extensive, compris- 

 ing many species of diverse genera ; and it may sometimes be 

 difficult to say that a form which clearly belongs to a given associa- 

 tion (or as Weismann has called it, a "mimicry ring") is more 

 closely assimilated to one constituent member of that association 

 than to another. Some species of Mi/lothris is generally considered, 

 with good reason, to be the central model controlling, so to speak, 

 the general aspect of each of these Pierino assemblages ; but it will 

 often happen that a Lenceronia female for instance, which is a mem- 

 ber of one of these assemblages, will show a greater likeness to 

 another subordinate member than to the central Mi^lothria. 

 Further consideration of these mat^^ters would lead us into the great 

 question of Mimicry, which is not our primary subject on the 

 present occasion ; and we must be content to note that these 

 divergent members of the female sex are not simply partners in 

 mimetic pairs, each pair consistmg only of mimic and model, but 

 are constituents, in several cases somewhat outlying ones, of more 

 or less extensive " mimicry rings," or, to use again a term perhaps 

 less open to objection, " homoeochromatic associations." 



Let us now consider what light these various facts are able to 

 throw upon the use and significance of sexual dimorphism. We 

 have seen that in many cases of sexual diversity the female is 

 characterised by a greater prevalence of dark pigment, resulting 

 frequently in a comparative dulness of colouring. In other 

 instances the female may show a specially close resemblance to 

 certain inanimate objects, such as dead leaves. Or again the 

 female may depart in great measure from the ordinary standard of 

 the species, and may become a more or less exact copy of a butterfly 

 of another species, sometimes far removed in point of affinity. 



Now the one common element in these difterent manifestations 

 of female divergence is the protection afibrded thereby to the 

 individual against the attacks of its enemies. It is true that the 

 subject of mimicry gives rise to some difference of opinion among 

 naturalists; but without going into matters of dispute, it will be 

 quite safe for us to say that there is a very considerable measure of 

 agreement that many conspicuous forms of insect life are relatively 

 immune from attack ; and that other insects which resemble the 

 immune forms are enabled by their resemblance to enjoy at least 



