234 THE DESCENT OF MAM, 



PART 11. 



SEXUAL SELECTION. 



CHAPTER VIII. 



PRIiq^CIPLES OF SEXUAL SELECTION. 



Secondary sexual characters Sexual selection Manner of action 

 Excess of males Polygamy The male alone generally modified 

 through sexual selection Eagerness of the male Variability of 

 the male Choice exerted by the female Sexual compared with 

 natural selection Inheritance, at corresponding periods of life, 

 at corresponding seasons of the year, and as limited by sex 

 Relations between the several forms of inheritance Causes why 

 one sex and the young are not modified through sexual selection 

 Supplement on the proportional numbers of the two sexes 

 throughout the animal kingdom The proportion of the sexes in 

 relation to natural selection. 



With animals which have their sexes separated, the 

 males necessarily differ from the females in their organs of 

 reproduction; and these are the primary sexual characters. 

 But the sexes often differ in what Hunter has called secondary 

 sexual characters, which are not directly connected with 

 the act of reproduction; for instance, the male possesses 

 certain organs of sense or lr>PAr>-r>finn, nf -^yliinh fl^p f^pmir^ 

 i s quite "destitute, or has them mor^ 1v'g-hly-dftvp|oped. in 

 order t hat lie m a ^ readily ^^ad^^-reack-ker-f-xjj- again the 

 male "Has special organs of prehension for holding her 

 securely. These latter organs, of infinitely diversified 

 kinds, graduate into those which are commonly ranked as 

 primary, and in some cases can hardly be distinguished 

 from them; we see instances of this in the complex append- 

 ages at tlie apex of tlie abdomen in male insects. Unless 

 indeed we confine the term *' primary '^ to the reproductive 



