THE MECHANISM OF DETUMESCENCE.

I.

The Psychological Significance of Detumescence—The Testis and the Ovary—Sperm Cell and Germ Cell—Development of the Embryo—The External Sexual Organs—Their Wide Range of Variation—Their Nervous Supply—The Penis—Its Racial Variations—The Influence of Exercise—The Scrotum and Testicles—The Mons Veneris—The Vulva—The Labia Majora and their Varieties—The Pubic Hair and Its Characters—The Clitoris and Its Functions—The Anus as an Erogenous Zone—The Nymphæ and their Function—The Vagina—The Hymen—Virginity—The Biological Significance of the Hymen.

In analyzing the sexual impulse we have seen that the process whereby the conjunction of the sexes is achieved falls naturally into two phases: the first phase, of tumescence, during which force is generated in the organism, and the second phase, of detumescence, in which that force is discharged during conjugation.[[72]] Hitherto we have been occupied mainly with the first phase, that of tumescence, and with its associated psychic phenomena. It was inevitable that this should be so, for it is during the slow process of tumescence that sexual selection is decided, the crystallizations of love elaborated, and, to a large extent, the individual erotic symbols determined. But we can by no means altogether pass over the final phase of detumescence. Its consideration, it is true, brings us directly into the field of anatomy and physiology; while tumescence is largely under control of the will, when the moment of detumescence arrives the reins slip from the control of the will; the more fundamental and uncontrollable impulses of the organism gallop on unchecked; the chariot of Phaëthon dashes blindly down into a sea of emotion.

Yet detumescence is the end and climax of the whole drama; it is an anatomico-physiological process, certainly, but one that inevitably touches psychology at every point.[[73]] It is, indeed, the very key to the process of tumescence, and unless we understand and realize very precisely what it is that happens during detumescence, our psychological analysis of the sexual impulse must remain vague and inadequate.

From the point of view we now occupy, a man and a woman are no longer two highly sensitive organisms vibrating, voluptuously it may indeed be, but vaguely and indefinitely, to all kinds of influences and with fluctuating impulses capable of being directed into any channel, even in the highest degree divergent from the proper ends of procreation. They are now two genital organisms who exist to propagate the race, and whatever else they may be, they must be adequately constituted to effect the act by which the future of the race is ensured. We have to consider what are the material conditions which ensure the most satisfactory and complete fulfillment of this act, and how those conditions may be correlated with other circumstances in the organism. In thus approaching the subject we shall find that we have not really abandoned the study of the psychic aspects of sex.

The two most primary sexual organs are the testis and the ovary; it is the object of conjugation to bring into contact the sperm from the testis with the germ from the ovary. There is no reason to suppose that the germ-cell and the sperm-cell are essentially different from each other. Sexual conjugation thus remains a process which is radically the same as the non-sexual mode of propagation which preceded it. The fusion of the nuclei of the two cells was regarded by Van Beneden, who in 1875 first accurately described it, as a process of conjugation comparable to that of the protozoa and the protophyta. Boveri, who has further extended our knowledge of the process, considers that the spermatozoon removes an inhibitory influence preventing the commencement of development in the ovum; the spermatozoon replaces a portion of the ovum which has already undergone degeneration, so that the object of conjugation is chiefly to effect the union of the properties of two cells in one, sexual fertilization achieving a division of labor with reciprocal inhibition; the two cells have renounced their original faculty of separate development in order to attain a fusion of qualities and thus render possible that production of new forms and qualities which has involved the progress of the organized world.[[74]]

While in fishes this conjugation of the male and female elements is usually ensured by the female casting her spawn into an artificial nest outside the body, on to which the male sheds his milt, in all animals (and, to some extent, birds, who occupy an intermediate position) there is an organic nest, or incubation chamber as Bland Sutton terms it, the womb, in the female body, wherein the fertilized egg may develop to a high degree of maturity sheltered from those manifold risks of the external world which make it necessary for the spawn of fishes to be so enormous in amount. Since, however, men and women have descended from remote ancestors who, in the manner of aquatic creatures, exercised functions of sperm-extrusion and germ-extrusion that were exactly analogous in the two sexes, without any specialized female uterine organization, the early stages of human male and female fœtal development still display the comparatively undifferentiated sexual organization of those remote ancestors, and during the first months of fœtal life it is practically impossible to tell by the inspection of the genital regions whether the embryo would have developed into a man or into a woman. If we examine the embryo at an early stage of development we see that the hind end is the body stalk, this stalk in later stages becoming part of the umbilical cord. The urogenital region, formed by the rapid extension of the hind end beyond its original limit, which corresponds to what is later the umbilicus, develops mainly by the gradual differentiation of structures (the Wolffian and Müllerian bodies) which originally exist identically in both sexes. This process of sexual differentiation is highly complex, so that it cannot yet be said that there is complete agreement among investigators as to its details. When some irregularity or arrest of development occurs in the process we have one or other of the numerous malformations which may affect this region. If the arrest occurs at a very early stage we may even find a condition of things which seems to approximate to that which normally exists in the adult reptilia.[[75]] Owing to the fact that both male and female organs develop from more primitive structures which were sexually undifferentiated, a fundamental analogy in the sexual organs of the sexes always remains; the developed organs of one sex exist as rudiments in the other sex; the testicles correspond to the ovaries; the female clitoris is the homologue of the male penis; the scrotum of one sex is the labia majora in the other sex, and so throughout, although it is not always possible at present to be quite certain in regard to these homologics.

Since the object to be attained by the sexual organs in the human species is identical with that which they subserve in their pre-human ancestors, it is not surprising to find that these structures have a clear resemblance to the corresponding structures in the apes, although on the whole there would appear to be in man a higher degree of sexual differentiation. Thus the uterus of various species of semnopithecus seems to show a noteworthy correspondence with the same organ in woman.[[76]] The somewhat less degree of sexual differentiation is well shown in the gorilla; in the male the external organs are in the passive state covered by the wrinkled skin of the abdomen, while in the female, on the contrary, they are very apparent, and in sexual excitement the large clitoris and nymphæ become markedly prominent. The penis of the gorilla, however, more nearly resembles that of man, according to Hartmann, than does that of the other anthropoid apes, which diverge from the human type in this respect more than do the cynocephalic apes and some species of baboon.