We now come to the last of the three classes of facts, which I have selected as presenting the greatest amount of difficulty with respect to distribution, on the view that not only all the individuals of the same species have migrated from some one area, but that allied species, although now inhabiting the most distant points, have proceeded from a single area, the birthplace of their early progenitors.
Geografi banakuntzari dagokionez zailtasun handienekotzat aukeratu ditudan hiru egitate motetarik azkena aztertzera goaz orain, honako hau dioen hipotesi honen barruan, hots, espezie bereko banako guztiak ez ezik, espezie ahaideak ere, egun punturik urrunenetan bizi arren, leku bakar batetik migraturikoak direla: antzinako beren gurasolehenen sorlekutik.