Thus, supposing the two hypotheses - special creation and evolution by natural selection - are to be tested by the directly-observed facts assigned in their support, then, if the hypothesis of evolution by natural selection is to be rejected because there are no directly-observed facts which prove it, the hypothesis of special creation must be rejected for the same reason. In fact, it would be impossible to arrive at any conclusion by such a line of argument.

On the subject of the time which would be required for the evolution of a living being of advanced type, the difficulty is thus cogently propounded. " If we think of the vast distance over which Darwin conducts us, from the jelly-fish lying on the primaeval beach to man as we know him now, if we reflect that the prodigious changes requisite to transform one into the other are made up of a chain of generations each advancing by a minute variation from the form of its predecessor, and if we further reflect that these successive changes are so minute that, in the course of our historical period - say three thousand years - this progressive variation has not advanced by a single step perceptible to our eyes, in respect to man or the animals or plants with which man is familiar, we shall admit that for a change so vast, of which the smallest link is longer than our recorded history, the biologists are making no extravagant claim when they demand at least many hundred millions of years for the accomplishment of the stupendous process." In reply to this Herbert Spencer, setting aside the statement that the jellyfish is a remote ancestor of man, quotes again from a portion of the essay previously referred to where the writer, after admitting that those who know nothing of the science of life may naturally think the hypothesis that all races of beings, man inclusive, may in process of time have been evolved from the simplest monad a "ludicrous one", continues: "But for the physiologist who knows that every individual being is so evolved, who knows further that in their earliest condition the germs of all plants and animals whatever are so similar that there is no appreciable distinction among them which would enable it to be determined whether any particular molecule is the germ of a Conferva or of an Oak, of a Zoophyte or of a ' Man' - for him to make a difficulty of the matter is inexcusable. Surely if a single cell, when subjected to certain influences, becomes a man in the space of twenty years, there is nothing absurd in the hypothesis that under certain other influences a cell may in the course of millions of years give origin to the human race."

In regard to the time required for the alleged evolutionary changes, he accepts Lord Kelvin's proposition to the effect that, " life cannot have existed on the earth for more than a hundred million years". At the same time it is pointed out that the proposition is open to doubt. Other geologists, quoted by Huxley in his lectures on evolution, assert that five hundred million years were occupied in the completion of the Tertiary formations, and in that case the period may be taken as the measure of the duration of the evolution of the horse; but the lecturer goes on to suggest that he is not much concerned about the discrepancies in calculations as to time, the chief point of enquiry being " is it a fact that evolution took place?" That question being answered, the time required for the process may be left to be determined by the physicist and the astronomer.

Herbert Spencer, however, waiving all criticism, accepts the lower estimate of one hundred million years as the time required, and proceeds to compare the changes in the development of the embryo with the evolutionary changes, as exhibited in the Tertiary formation, in regard to their extent and the time occupied by them.

" The nine months of human gestation, more exactly stated, is 280 days, that is 6720 hours or 403,200 minutes. Thus, then, the total change from the nucleated cell constituting the human ovum to the developed structures of the infant just born, is divisible into 403,200 changes each occupying a minute. No one of these changes is appreciable by the eye or even by a micrometer." Turning to the other member of the comparison, the writer proceeds to contrast the evolution of a man from a primitive protozoon with the evolution of the infant from the protoplasm in the cell of the human ovum. In doing this he supposes the developmental changes from the jellyfish to the man to be equal in their number to those gone through by the foetus. And in order to arrive at a result he divides 100,000,000 years by 403,200 changes, a simple sum which gives in its quotient a period of nearly 250 years as the interval available for an amount of change equal to that which the foetus undergoes in a minute. If, instead of the human ovum, the ovum of a rabbit had been taken for comparison, the contrast in point of time would have been of necessity more striking, as similar changes to those which occur in the human ovum during nine months take place in that of the rabbit in a few weeks.

It will be observed that the argument is not directed to the proof that man was evolved from a jelly-fish or other primitive protozoon, but rather to the fact of there having been according to the lowest estimate ample time for the process, seeing that in the ordinary course of things a child is evolved from a mass of protoplasm in a few months, and advances to the condition of a man in the course of some twenty years.

Enough has been said to leave no room for reasonable doubt that what-ever may be its limitation, evolution is a natural process, the successive steps of which may be observed and recognized, as in the examples which have been given.

It is, of course, open to anyone to oppose the proposition that every existing organism, animal and plant, was developed from some original and undifferentiated protoplasmic matter, just as the foetus is developed from a microscopic speck of protoplasm. Nor is it required for the present purpose that the proposition should be accepted. It cannot be denied, on the other hand, that under the influence of changes in the environment certain important alterations of form and function do happen, and are indicated by the presence among existing beings of organs and parts which are so placed as to be devoid of any functional value, while a comparison of them with similar and more developed parts in extinct races necessarily leads to the presumption that they may be, and most probably are, rudimentary or vestigial remains modified by the laws of heredity and the influence of natural and artificial selection.

Leaving now the general for the particular, the question which presents itself relates to the facts which are offered by the anatomist and the palaeontologist, in regard to structure and conformation, bearing upon the statement that the horse may be traced through a long line of extinct mammals back to the earliest mammals of the Tertiary period.