fore you leave this room? The hole being unaltered in size, the number of molecules undiminished, this apparent paradox can only be explained by again supposing the size of the molecules to be diminished almost infinitely—so that, instead of entering at the rate of one hundred millions every second, they troop in at a rate of something like three hundred trillions a second! I have done the sum, but figures when they mount so high cease to have any meaning, and such calculations are as futile as trying to count the drops in the ocean.
In studying this fourth state of matter we seem, at length, to have within our grasp and obedient to our control the little indivisible particles which, with good warrant, are supposed to constitute the physical basis of the universe. We have seen that, in some of its properties, radiant matter is as material as this table, while in other properties it almost assumes the character of radiant energy. We have actually touched the border-land where matter and force seem to merge into one another, the shadowy realm between known and unknown, which for me has always had peculiar temptations. I venture to think that the greatest scientific problems of the future will find their solution in this border-land, and even beyond; here, it seems to me, lie ultimate realities, subtile, far-reaching, wonderful.
"Yet all these were, when no man did them know,
Yet have from wisest ages hidden beene;
THE subject on which I address you to-day is one which is still veiled in much obscurity—so much so, indeed, that it is barely alluded to by evolutionists, is not touched upon by physiologists, and is regarded by the popular mind, even the intelligent popular mind, as wholly beyond the possible ken of human science.
1. Defining the Subject.—In regard to the origin of sex there are two distinct yet closely-related questions: 1. The origin of sex in the history of the individual; 2. The origin of sex in the history of the organic kingdom. The one question is, What are the conditions which determine the appearance of the one or the other sex in the de-
- In order to explain the forms of expression in some parts of this article, it is necessary to state that it was delivered in 1877 as a lecture to the class in Comparative Physiology in the University of California, and again in 1878 to the class in Physiology of the medical department of the same.