252 TIIE PRINCIPLES OF [Part II. 



'with frogs and toads. Throughout the great class of in- 

 sects the males almost always emerge from the pupal state 

 before the other sex, so that they generally swarm for a 

 time before any females can be seen. 3 The cause of this 

 difference between the males and females in their periods 

 of arrival and maturity is sufficiently obvious. Those males 

 which annually first migrated into any country, or which 

 in the spring were first ready to breed, or were the most 

 eager, would leave the largest number of offspring ; and 

 these would tend to inherit similar instincts and constitu- 

 tions. On the whole, there can be no doubt that with al- 

 most all animals, in which the sexes are separate, there is a 

 constantly recurrent struggle between the males for the 

 possession of the females. 



Our difficulty in regard to sexual selection lies in un- 

 derstanding how it is that the males which conquer other 

 males, or those which prove the most attractive to the fe- 

 males, leave a greater number of offspring to inherit their 

 superiority than the beaten and less attractive males. 

 Unless this result followed, the characters which gave to 

 certain males an advantage over others, could not be per- 

 fected and augmented through sexual selection. When 

 the sexes exist in exactly equal numbers, the worst-endowed 

 males will ultimately find females (excepting where polyg- 

 amy prevails), and leave as many offspring, equally well 

 fitted for their general habits of life, as the best-endowed 

 males. From various facts and considerations, I former- 

 ly inferred that with most animals, in which secondary 



3 Even with those of plants in which the sexes are separate, the male 

 Qowers are generally mature before the female. Many hermaphrodite 

 plants are, as first shown by C. K. Sprengel, dichogamous ; that is, their 

 male and female organs are not ready at the same time, so that they can- 

 hot be self-fertilized. Now with such plants the pollen is generally ma- 

 ture in the same flower before the stigma, though there are some excep- 

 tional species in which the female organs are mature before the male. 



