C.
Watson has remarked, "in receding from polar toward equatorial latitudes, the Alpine or mountain flora really become less and less Arctic.
" Besides these identical and closely allied forms, many species inhabiting the same widely sundered areas, belong to genera not now found in the intermediate tropical lowlands.
These brief remarks apply to plants alone; but some few analogous facts could be given in regard to terrestrial animals.
In marine productions, similar cases likewise occur; as an example, I may quote a statement by the highest authority, Prof.