PROPORTION OF THE SEXES. 293 



instance, fishes and cirripedes) in which two or more males 

 appear to be necessary for the fertilization of the female; 

 and the males accordingly largely preponderate, but it is 

 by no means obvious how this male-producing tendency 

 could have been acquired. I formerly thought that when 

 a tendency to produce the two sexes in equal numbers was 

 advantageous to the species it would follow from natural 

 selection, but I now see that the whole problem is so intri- 

 cate that it is safer to leave its solution for the future. 



