many variations, and among these the special variations to which the vertebrate type is due. It is quite clear that wherever the external surroundings were the same or nearly the same, the variations introduced would be the same or nearly the same. Now, it is far more probable that external surroundings should be the same or nearly the same in many places than that each spot should be absolutely unlike every other spot in these particulars. The beginnings of the vertebrate order would show themselves simultaneously, or at any rate independently, in many places wherever external conditions were sufficiently similar. And the unity of the plan in the vertebrata would be due, not to absolute unity of ancestry, but to unity of external conditions at a particular epoch in the descent of life. Hence it follows that the separation of animals into orders and genera and even into species took place, if not for the most part yet very largely, at a very early period in the history of organic evolution. Of course the descendants of any one of the original vertebrata might, and probably in not a few cases did, branch off into new subdivisions and yet again into further subdivisions, and we are always justified in looking for unity of ancestry among all the species. But it is also quite possible that any species may be regularly descended, without branching off at all, from one of the originals, and that other species that resemble it may owe the resemblance simply to very great similarity of external conditions. To find, for instance, the unity of ancestry between man and the other animals, it will certainly be necessary to go back to a point in the history of life when living creatures were as yet formless, undeveloped--the materials, as we may call them, of the animal creation as we now see it, and not in any but a strictly scientific sense, what we mean when we ordinarily speak of animals. The true settlement of such questions as these can only be obtained when long and patient study shall have completed Darwin's investigations by determining under what laws and within what limits the slight variations which characterise each individual animal or plant are congenitally introduced into its structure. As things stand the probabilities certainly are that a creature with such especial characteristics as man has had a history altogether of his own, if not from the beginning of all life upon the globe, yet from a very early period in the development of that life. He resembles certain other animals very closely in the structure of his body; but the part which external conditions had to play in the earliest stages of evolution of life must have been so exceedingly large that identity or close similarity in these external conditions may well account for these resemblances. And the enormous gap which separates his nature from that of all other creatures known, indicates an exceedingly early difference of origin.