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 animals appear beak become bees believe belonging birds breeds cause cells characters climate closely allied colour continent crossed crustaceans degree developed difficulty distinct species domestic doubt effects eggs embryo existing extinct extremely facts favourable fertilised fertility flowers formation forms fossil Fritz Müller genera genus geological Glacial period gradations greater number habits Hence hybrids important increase individuals inhabitants inherited insects instance instincts intercrossing intermediate kind lamellæ larvæ less living male mammals manner marsupial migration modified descendants natural selection naturalists nearly nest occasionally oceanic islands offspring organisation organs Origin of Species parent peculiar perfect pigeon pistil plants pollen present principle probably produced quadrupeds ranked reciprocal crosses remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive supposed swimbladder tend theory tion variability variations varieties vary whilst whole wings young