In propagation by germs or buds, the same thing must hold true, only, as the offspring carries with it not the half, but only a small portion of the parental organism, its impress will be less powerful, and the new organism will more readily be affected by external influences. When we come to propagation by spores or single cells, and still more to sexual propagation by the union of single cells of two progenitors, it becomes more difficult to see how the type of the two parents, and of a long line of preceding ancestors, can be maintained so perfectly. Of the fact that it is maintained there can be no doubt. Not only do species breed true and remain substantially the same for immense periods, but the characters of individual parents and their ancestors repeat themselves, to a great extent, in their offspring. Thus the cross between the white and black varieties of the human species perpetuates itself to such an extent, that a single cross of black blood leaves traces for a number of generations. In the Spanish American States and the West Indies, where the distinction is closely observed, the term ‘octoroon’ is well known, as applied to Creoles who have seven-eighths of white to one-eighth of black blood in their composition. In the case of what is called ‘atavism,’ this recurrence to the characters of ancestors is carried to a much further extent. In breeding animals, it is not uncommon to find the peculiar features of generations of ancestors long since extinct cropping up occasionally in individuals. Thus, stripes like those of the ass along the back and down the shoulders, occasionally appear on horses whose immediate ancestors for many generations back showed nothing of the sort; and even stripes across the legs like those of the zebra occur quite unexpectedly, and testify to the common descent of the various species of the horse tribe from a striped ancestor. How these ancestral peculiarities can be transmitted through many generations, each individual of which originated from a single microscopic cell which had been fructified by another cell, is one of the greatest mysteries of nature. It may assist us in forming some idea of the possibility of a solution to remember what has been proved as to the dimensions of atoms. Their order of magnitude is that of a cricket-ball to the earth. In a single microscopic cell, therefore, there may be myriads of such atoms circling round one another and forming infinitesimal solar systems, of infinite complexity and variety. Darwin’s theory of ‘Pangenesis’ supposes that some of the actual identical atoms which formed part of ancestral bodies are thus transmitted through their descendants for generation after generation, so that we are literally ‘flesh of the flesh’ of the primæval creature who was developed into man in the later tertiary or early glacial period. Haeckel, more plausibly, suggests that not the identical atoms, but their peculiar motions and