240 THE DESCENT OF MAN. 



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 breeding before the females, so that many 

 males are ready to contend for each female.'HI am informed 

 by Mr. Jenner Weir, that the bird-catcherSlissert 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 Eay^s wagtail {Budytes 

 Rail) before lie saw a single female. Mr. Gould has ascer- 

 tained 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. CPln'oughout 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.f 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 the most eager, would leave the 

 largest number of offspring; and these would tend to in- 

 herit similar instincts and constitutionsTj It must be borne 

 in mind that it would have been impossible to change very 

 materially the time of sexual maturity in the females with- 

 out at the same time interferiing with the period of the 



*J. A. Allen on the "Mammals and Winter Birds of Florida," 

 Bull. Comp. Zoology, Harvard College, p. 268. 



f Even witli tliose plants in wliicli the sexes are separate, the male 

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

 C. K. Sprengel, many hermaphrodite plants are dichogamous; 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 pollen 

 is in general matured before the stigma, though there are exceptional 

 Cftses io which the female organs are beforehand. 



