There is no reason to doubt that the same sequence of events occurs in nature apart from man's interference. Changes occur in the earth's surface, or the organism is transported by currents of water or air into new conditions. The germ-plasm is "disturbed," "shaken" or "shocked" by those new conditions, and a variation, in several structures and qualities of the offspring subsequently produced, follows. Then also follows the selection of one of the new varieties by survival of the fitter to the new conditions into which the organism has been transported or have developed in the region where it was previously established. This process of germ-variation is obviously as necessary and constant a feature of the living organism as is the variation in the contour of land and sea and in the extent of the polar ice-cap–a necessary feature of the physical conditions of the terrestrial globe. But it is the fashion with a certain school of writers nowadays to declare that "variation" in organisms is a "mystery" unsolved. Another very common and almost universal error is to overlook the fact that variation is constitutional and affects whole systems of organs and their deeply related parts, and is _not_, as it is so frequently and erroneously assumed to be, a mere local affair of patches and scraps visible on this or that part of the surface of an animal or plant. These superficial "marks," readily seen and noted by the collector, are rarely of any life-saving importance: they are but the outward and visible signs of deep-lying physiological or constitutional change or variation. The varying organism has, like Hamlet, "that within which passeth show" and the superficial variations (like his "inky cloak" and other customary features of mourning) are but "the trappings and the suits" of a deep-lying change. Variation is not an inexplicable mystery, nor, on the other hand, are "varieties" sufficiently dealt with and their nature appreciated when one or two surface peculiarities are enumerated by which the collector can recognize them. A deeper study of the varying organism is both possible and needed. If the gradual formation of new species from ancestral species is a true account of the matter, we must expect to find, at any rate here and there, if not frequently, traces of the process–for instance, gradations, or series of intermediate forms, connecting new, well-established species with the ancestral form or with one another. We do find such gradations–sometimes more, sometimes less, completely persisting over a wide tract of country, or discoverable in the fossiliferous deposits containing the remains of extinct animals.