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 ancient 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 Gärtner genera genus geological geological period Glacial period gradations greater number habits Hence hybrids hybrids produced important increase individuals inhabitants inherited insects instance instincts intercrossing intermediate kind lamellæ larvæ less living males mammals manner marsupial migration modified descendants natural selection naturalists nearly nest occasionally oceanic islands offspring organisation organs paleozoic parent peculiar perfect pigeon pistil pollen present principle probably produced quadrupeds ranked reciprocal crosses remarked resemblance rudimentary seeds slight South America stamens sterility structure struggle successive supposed tend theory tion trees variability variations varieties vary whilst whole wings young