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according active already anabolic animals appear asexual associated become beginning birds body called changes characters colonies colour common comparatively conclusion connection continuity contrast Darwin determination differentiation distinct divides division eggs elements embryo essential evolution explanation expression fact factors favour fertilisation fishes flowers frequently functions further growth habit hermaphroditism higher illustrations important increase individual influence insects interesting interpreted katabolic known latter less living male and female material natural normal noted nucleus nutritive observed occur offspring organs origin ovary ovum parasitic parent parthenogenetic pass period physiological plants polar position possible preponderance present probably problem produce protoplasm referred regard remain reproductive cells result secondary seems seen selection separate sexual reproduction sexual selection shown sometimes species sperm stage structure suggested tend theory tion true union units usually variations Weismann young
Page 275 - Gavest thou the goodly wings unto the peacocks? Or wings and feathers unto the ostrich? Which leaveth her eggs in the earth, And warmeth them in the dust, And forgetteth that the foot may crush them, Or that the wild beast may break them. She is hardened against her young ones, As though they were not hers...
Page 38 - 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 intricate that it is safer to leave its solution for the future.
Page 9 - To sum up on the means through which, as far as we can judge, sexual selection has led to the development of secondary sexual characters. It has been shown that the largest number of vigorous offspring will be reared from the pairing of the strongest and best-armed males...