Origin of Species

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