[S] More observations and fuller knowledge on this latter point and on the relative numbers of the sexes in different species are much to be desired. It is clear that the number of offspring mainly depends upon the number of females. But if it be true that good times and favourable conditions lead to an increased production of females, while hard times and unfavourable conditions lead to a relative increase of males, then it is evident that good times will lead to a more rapid increase and hard times to a less rapid increase of the species. Suppose, for example, in a particular district food and other conditions were especially favourable for frogs. Among the well-nourished tadpoles there would be a preponderance of females. In the next generation the many females would produce abundant offspring (for one male may fertilize the ova laid by several females). There would be a greater number of tadpoles to compete for the same amount of nutriment. They would be less nourished. There would be less females; and in the succeeding generation a diminished number of tadpoles. Thus to some extent a balance between the number of tadpoles and the amount of available nutrition would be maintained. These conclusions are, perhaps, too theoretical to be of much value, while the tendency here indicated would be but one factor among many. [T] "Origin of Species," pp. 62, 63. [U] "Animals and Plants under Domestication," vol. ii. p. 177. [V] I may here draw attention to the fact that the bats whose wing-bone measurements were given above are those which have so far survived and escaped such elimination as is now in progress. [W] "Origin of Species," p. 109. [X] "Darwinism," p. 106. [Y] Ibid. p. 106. [Z] Proceedings Liverpool Biological Society, 1889. [AA] Since this chapter was written, Mr. Poulton has published his interesting and valuable work on "The Colours of Animals," from which I have contrived to insert one or two additional examples. [AB] _Ann. and Mag. Nat. Hist._, September, 1889, p. 209, quoted by Poulton, "Colours of Animals," p. 55. [AC] Nature, vol. xxxv. p. 77.