I shall comment later on the points here raised, but we should not let this opportunity pass without noticing, that even if the pairing were to follow according to the method here imagined, still the argument breaks down at the critical point, for there is no evidence that the more precocious females would rear a larger number of offspring than the more normal females, or even those that breed somewhat later. The greater eagerness of the males which has been observed in so many different classes of animals is accounted for as follows:— “But it is difficult to understand why the males of species, of which the progenitors were primordially free, should invariably have acquired the habit of approaching the females, instead of being approached by them. But in all cases, in order that the males should seek efficiently, it would be necessary that they should be endowed with strong passions; and the acquirement of such passions would naturally follow from the more eager leaving a larger number of offspring than the less eager.” Thus we are led to the rather complex conclusion, that the more eager males will leave more descendants, and those that are better endowed with ornaments will be the ones selected. But unless it can be shown that there is some connection between greater eagerness and better ornamentation, it might often occur that the less ornamented were the more eager individuals, in which case there would be an apparent conflict between the two acquirements. After giving some cases of the greater variability of the males, in respect to characters that are not connected with sexual selection, and presumably not the result of any kind of selection, Darwin concludes: “Through the action of sexual and natural selection male animals have been rendered in very many instances widely different from their females; but independently of selection the two sexes, from differing constitutionally, tend to vary in a somewhat different manner. The female has to expend much organic matter in the formation of her ova, whereas the male expends much force in fierce contests with his rivals, in wandering about in search of the female, in exerting his voice, pouring out odoriferous secretions, etc.: and this expenditure is generally concentrated within a short period. The great vigor of the male during the season of love seems often to intensify his colors, independently of any marked difference from the female. In mankind, and even as low down in the organic scale as in the Lepidoptera, the temperature of the body is higher in the male than in the female, accompanied in the case of man by a slower pulse. On the whole, the expenditure of matter and force by the two sexes is probably nearly equal, though effected in very different ways and at different rates.”