We shall be obliged, of course to invite our distinguished European party to join us on this side of the Atlantic, as their own narrow and contracted continent furnishes no proper field for determining the problem in question. We shall insist upon one condition only: "_That they shall never leave the warm temperate zone in which we shall set out on our expedition, except to pass halfway into an adjoining zone as is the habit, at times, with plants and animals_." This condition will have to be rigidly observed, otherwise our expedition would be of no scientific value to future generations. As we shall have plenty of time to provide the necessary outfit, we will appoint Mr. Darwin purveyor-general of the party, and hold him responsible for any misadventure. We will arrange for the expedition to start in the early autumn of the year of our Lord 831,800, or about twenty thousand years before the earth shall reach its next superior limit of eccentricity,--all of us eager, of course, to brave the climatic vicissitudes of the journey, and to solve the "great problem of the ages," which is, to determine how the gigantic elephantoids of the Eocene period managed to cross the thermal equator, and pass into the present arctic regions of our globe. As "the king never dies," so the old southern Ice-monarch will be succeeded by the young northern one, at about the period named. We shall then have a decided advantage over our predecessors, the plants and animals, in their journey southward, since we shall know the exact route they took, and need only follow it. Presumably they had no such information, nor had they either chart or compass to guide them,--a circumstance which Mr. Darwin has not sufficiently taken into account in predicating intelligence of his favorite pedestrians. Besides, these vegetal and animal forms had one difficulty to encounter which we shall not experience. With all the northern forms driven down into the Central American states, they must have been sadly crowded for room, especially near the Isthmus. The social conifers must have monopolized all the more favored sites on the mountain sides and tops, while the humbler denizens of the forest must have contented themselves with still more limited quarters. The more impatient animals, for lack of necessary forage, must have crowded through the Isthmus only to be driven back by the tropical heats to their proper isotherms.