divisible into 403,200 changes each occupying a minute. No one of these changes is appreciable by the naked eye, or even by a micrometer. Turn now to the other member of the comparison. Let us suppose the total change between the primitive Protozoon, or nucleated cell, and the human being proceeding from it, to be divided into increments of change, equal in their number to those gone through by the fœtus. To compare the two sets of changes we divide 100,000,000 years by 403,200. What is the result? We get nearly 250 years as the interval available for an amount of change equal to that which the fœtus undergoes in a minute. Another way of presenting the facts yields results still more striking. Many creatures of superior types take more than a year to reach the reproductive age, and even among insects there are some which retain their larval forms for a longer period. But, bearing in mind that even among the Vertebrata the immense majority of species reach the reproductive age in a year, while some of them, as the inferior Rodents, reproduce in a shorter term, and remembering that throughout the lower divisions of the undetermined phylogenetic series preceding the vertebrates, consisting of relatively small and simple creatures, the succession of generations was probably more rapid, we may fitly, contemplating the whole series, take a year as the equivalent for a generation. If so, it follows that to achieve the transformation of the Protozoon into Man, it requires only that in the space of 250 generations the change shall be as great as that which the human fœtus undergoes in a minute; or, otherwise stating the fact, it requires that each generation shall differ from the last by as much as the fœtus differs from itself after an interval of a fourth of a second.
Should it be urged that the successive stages of the transformation gone through by the infant do not represent fully the stages of transformation gone through in progressing from the primitive nucleated cell to the human being, but that there have been periods of excursive modification on various sides of the direct line, and periods in which there was no advance, or in which there was even some retrogression, it would still result that if, in one generation, there occurred as much change of form as the fœtus undergoes in a minute, the remaining 240 odd generations might be set aside for non-progressive changes: a sufficiently wide margin.
One more misconception embodied in Lord Salisbury's address remains to be noted—not a misconception peculiar to himself, but one which men at large entertain. Speaking of the groups of chemical elements, he says:—
