260 THE PRINCIPLES OF Part II. 



their males. During one spring he shot thirty-nine 

 males of Ray's wagtail (Budytes Baii) before he saw a 

 single female. Mr. Gould has ascertained by dissection, 

 as he informs me, that male snipes arrive in this 

 country before the females ; but this hardly concerns us, 

 as snipes do not breed here. In the case of fish, at the 

 period when the salmon ascend our rivers, the males in 

 large numbers are ready to breed before the females. 

 So it apparently is with frogs and toads. Throughout 

 the great class of insects 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 

 constitutions. On the whole there can be no doubt that 

 with almost 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 

 understanding how it is that the males which conquer 

 other males, or those which prove the most attractive 

 to the females, leave a greater number of offspring 

 to inherit their superiority than the beaten and less 



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

 flowers are generally mature before the female. Many hermaphrodite 

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

 their male and female organs are not ready at the same time, so thai 

 they cannot be self-fertilised. Now with such plants the pollen is 

 generally mature in the same flower before the stigma, though there 

 are some exceptional species in which the female organs are mature 

 before the male. 



