On the origin of species extract 11

31. It is a more important consideration, leading to the same result, as lately insisted on by Dr. Falconer, namely, that the period during which each species underwent modification, though long as measured by years, was probably short in comparison with that during which it remained without undergoing any change. P352
32. A group, when it has once disappeared, never reappears; that is, its existence, as long as it lasts, is continuous. P368