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 continent crossed crustaceans degree developed difficulty distinct species divergence doubt effects eggs embryo existing extinct extremely facts favourable females fertilised fertility flowers formation formerly forms fossil Fritz Müller genera genus geological Glacial period gradations greater number groups of species habits Hence hybrids hybrids produced important increase 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 paleozoic parent peculiar perfect pigeon pistil pollen present preserved principle probably produced quadrupeds ranked remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive supposed theory tion trees variability variations varieties vary whilst whole wings young