The Origin of Species by Means of Natural Selection: Or, The Preservation of Favored 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 color common continent crossed crustaceans degree developed difficulty distinct species domestic doubt 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 lamellæ larvæ less living male mammals manner marsupial migration modification modified descendants natural selection naturalists nearly nest offspring organs ORIGIN OF SPECIES 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 theory tion trees variability variations varieties vary whole wings young