On 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 amount analogous ancient animals appear Asa Gray become bees believe birds breeds cause cells characters cirripedes climate closely allied colour continuous crossed crustaceans degree difficulty distinct species divergence domestic doubt embryo Europe existing exterminated extinct extremely facts favourable fertility flowers formations forms fossil Gärtner genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hybrids hybrids produced important individuals inhabitants inherited insects instance instincts intercrossing intermediate land larvæ laws less living male mammals manner Marsupials migration modification modified descendants mongrels natural selection naturalists nearly nest occasionally offspring organisation origin of species perfect pigeons plants pollen present principle probably produced progenitor racter ranked reciprocal crosses remarked resemble rudimentary organs seeds Silurian slight South America sterility structure struggle successive supposed tend theory tion variability variations varieties vary whole widely