The peculiarities that, when coarsely emphasized, serve to distinguish different species of animals from one another, are repeated in more subtle gradations, as varieties among the different classes, and even different individuals of the human race. Here may be found, at least, faint echoes and distant reminiscences of facts that stand out in bold relief throughout the animal kingdom. The classification of sex is certainly one of those that offer an interesting opportunity for such comparison, especially in regard to the relations existing between the operations of the ganglionic, and those of the cerebro-spinal system. As the authors who have asserted the complete subordination of the brain to the instincts in woman, have thus, perhaps unconsciously, reduced her to the anatomical level of the crustacea; so those who, like Dr. Clarke, insist on the incompatibility between cerebral action and the process of ovulation, imply a predominance of ganglionic activity in women that must render them the physiological inferiors of the animals or individuals in whom no such incompatibility exists. Were such opposition between cerebral and ganglionic functions only noted when a rhythmical intermittence was introduced into the latter, and were such rhythm observed only in the phenomena of menstruation, it might indeed be possible to fix upon women a peculiar mark of physiological inferiority, almost sufficient to amount to a stigma. But rhythmical movement is characteristic of all physiological actions--of the beating of the heart, the secretions of the stomach, the congestion of the spleen, the circulation of the brain, quite as decidedly as of the ripening of cells in the ovary. The tidal waves described by Michelet have become the exclusive theme of his eloquence, mainly because his attention was not attracted to any but those connected with the more obvious phenomena of menstruation. But many tidal waves rise and cross each other in shorter or longer cycles--waves of pulse and of temperature, of sleep and wakefulness, intermittences of secretion and excretion. In regard to the latter, it is noticeable that an intermittent excretion, as of bile or urine, is provided for by a continuous secretion, and that the same is true of the excretion upon whose rhythm an erroneously exceptional emphasis has been laid--that of the menstrual fluid. Here, as elsewhere, the intermittent phenomenon is preceded by long-continued cell growth--effected by precisely such processes of cellular assimilation and metamorphosis as take place in the elements of the liver and the kidneys. The cell growth in question is effected in the ovaries; the final stage of the process, the rupture of the containing cell or ovisac, and escape of the ovule, is attended by a concentration of nervous activity in the ganglionic masses sending nerves to those organs--analogous to that which occurs in the solar plexus at periods of digestion; the fall of the ovule is itself