208 THE DESCENT OF MAN. 



be superfluous to give instances. Hence the females have the 

 opportunity of selecting one out of several males, on the suppo- 

 sition that their mental capacity suffices for the exertion of a 

 choice. In many cases special circumstances tend to make the 

 struggle between the males particularly severe. Thus the males 

 of our migratory birds generally arrive at their places of breed- 

 ing before the females, so that many males are ready to contend 

 for each female. I am informed by Mr. Jenner Weir, that the 

 bird-catchers assert that this is invariably the case with the 

 nightingale and blackcap, and with respect to the latter he can 

 himself confirm the statement. 



Mr. Swaysland of Brighton has been in the habit, during the 

 last forty years, of catching our migratory birds on their first 

 arrival, and he has never known the females of any species to 

 arrive before their males. During one spring he shot thirty-nine 

 males of Ray's wagtail (Budytes Rail) before he saw a single fe- 

 male. Mr. Gould has ascertained by the dissection of those 

 snipes which arrive the first in this country, that the males come 

 before the females. And the like holds good with most of the 

 migratory birds of the United States." The majority of the male 

 salmon in our rivers, on coming up from the sea, are ready to 

 breed before the females. So it appears to be with frogs and 

 toads. Throughout the great class of insects the males almost 

 always are the first to emerge from the pupal state, so that they 

 generally abound for a time before any females can be seen." 

 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 olfspring; and these 

 would tend to Inherit similar instincts and constitutions. It 

 must be borne in mind that it would have been impossible to 

 change very materially the time of sexual maturity in the fe- 

 males, without at the same time interfering with the period of 

 the production of the young — a period which must be determined 

 by the seasons of the year. On the who'e 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. 



^ J. A. Allen, on the 'Mammals and Winter Birds of Florida," Bull. 

 Comp. Zoology, Harvard College, p. 288. 



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

 flowers are generally mature before the female. As first shown by 

 C. K. Sprengrel, many hermaphrodite plants are diohog-amous ; that 

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

 that they cannot be self-fertilized. Now in such flowers, the pol- 

 len is in general matured before the sligma, though there are excep- 

 tional cases in which the female organs are beforehand. 



