The Origin of Species by Means of Natural Selection: Or, The Preservation of Favored Races in the Struggle for Life

accumulated adapted admit affinities allied species America analogous ancient appear beak become bees believe belonging birds breeds cause cells characters cirripedes climate closely allied colour continued crossed crustaceans degree developed difficulty distinct species divergence doubt effects eggs embryo existing exterminated extinct extremely facts favourable fertility flowers formation formerly forms fossil Fritz Müller genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hybrids important individuals inhabitants inherited insects instance instincts intercrossing kind lamellę larvę less living male mammals manner marsupials migration modified descendants natural selection naturalists nearly nest occasionally oceanic islands offspring organs parent peculiar perfect pigeons pistil pollen present preserved principle probably produced quadrupeds ranked reciprocal crosses remarked reproductive resemblance rudimentary seeds sexual selection slight South America stamens sterility structure struggle successive supposed theory tion trees variability variations vary whilst whole wings young