The Origin of Species by Means of Natural Selection

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