The Origin of Species by Means of Natural Selection: Or, The Preservation of Favoured Races in the Struggle for Life

accumulated adapted affinities allied species America ancient animals appear become bees believe birds breeds cause cells chapter characters cirripedes climate closely allied colour continuous crossed crustaceans Darwin degree developed difficulty distinct species domestic doubt eggs embryo Europe existence exterminated extinct extremely facts favourable fertility flowers formation forms fossil genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hermaphrodites hybrids important individuals inhabitants inherited insects instance instincts intercrossing intermediate larvae less living male mammals manner Marsupials migration modification modified descendants natural selection naturalists nearly nest offspring organisation organs Origin Origin of Species palaeozoic perfect pigeons pistil plants pollen present principle probably produced progenitor quadrupeds ranked remarked reproductive resemblance rudimentary seeds seems sexual selection Silurian slight South America sterility structure struggle successive supposed tend theory tion trees variability variations varieties vary whole widely wings