Natural Selection its power compared with man's selection its power on characters of trifling importance its power at all ages and on both sexes Sexual Selection. Variations neither useful nor injurious would not be affected by Natural Selection, and would be left a fluctuating element, as perhaps we see in the species called polymorphic. We shall best understand the probable course of Natural Selection by taking the case of a country undergoing some physical change, for instance, of climate. Natural Selection may modify and adapt the larva of an insect to a score of contingencies, wholly different from those which concern the mature insect. Natural Selection will modify the structure of the young in relation to the parent, and of the parent in relation to the young. Sexual Selection is, therefore, less rigorous than Natural Selection. To sum up the circumstances favourable and unfavourable to Natural Selection, as far as the extreme intricacy of the subject permits.