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

adapted admit affinities allied species America analogous ancient appear beak become bees believe belonging birds breeds cause cells characters climate closely allied colour continuous crossed crustaceans degree developed difficulty distinct species doubt effects eggs embryo existing extinct extremely facts favourable fertilised fertility flowers formations 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 intermediate kind lamellæ larvæ less living male mammals manner Marsupials migration modified descendants natural selection naturalists nearly nest occasionally occur oceanic islands offspring organisation organs parent peculiar perfect pigeon 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 variability variations varieties vary whilst whole wings young