Chap. V. CHARACTERS VARIABLE. 157 



less rigud in its action tlian ordinary selection, as it does not 

 entail death, bnt only gives fewer offspring to the less favored 

 males. Whatever tlie cause may be of the variability of sec- 

 ondary sexual characters, as they are highly variable, sexual se- 

 lection, will have had a wide scope for action, and may thus 

 readily have succeeded in giving to the species of the same 

 group a greater amount of difference in their sexual characters 

 tlian in other parts of their structure. 



It is a remarkable fact that the secosdary sexual differ- 

 ences between the two sexes of the same sjiecies arc generally 

 displayed in the very same parts of the organization in whicli 

 the different species of the same genus dilfer from each other. 

 Of this fact I will give two instances in illustration, the first 

 which hap])en to stand on my list; and, as the differences in 

 these cases are of a very unusual nature, the relation can hard- 

 ly be accidental. The same number of joints in the tarsi is a 

 character generally common to very large gi-oups of beetles, 

 but in the Engid:e, as Westwood has remarked, the number 

 varies greatly; and the number likewise differs in the two 

 sexes of the same species : again, in fossorial liymenoptera, the 

 manner of neuration of the wings is a character of the highest 

 importance, because common to large groups ; but in certain 

 genera the ncin-ation differs in the different species, and like- 

 wise in the two sexes of the same species. Sir J. Lubbock 

 has recently remarked that several minute crustaceans offer ex- 

 cellent illustrations of this law. " In Pontella, for instance, 

 the sexual characters arc afforded mainly l)y the anterior an- 

 tenna) and by the fifth pair of legs : the specific differences 

 also are principally given by these organs." This relation has 

 a clear meaning on my view of the subject : I look at all th(! 

 species of the same genus as ha^nng as certainly descended 

 from the same progenitor as have the two sexes of any one of 

 the species. Conseijuently, whatever part of the structure of 

 the common progenitor, or of its early descendants, became 

 A-ariable, variations of this part Avould, it is highly jiroljable, be 

 taken advantage of by natural and sexual selection, in order to 

 fit the several species to their several j)lac(\s in the economy of 

 Nature, and likewise to fit the two sexes of the same S]iecies to 

 each other, or to fit the males and females to different habits of 

 life, or the males to struggle with other males for the jiosses- 

 sion of the females. 



Finally, then, I conclude that the greater variability of 

 specific characteis, or those which distinguish species from 



