MOST errors arise not from absolute ignorance but from an inexact conception of just those things which one thinks one knows best. This is especially true in the sphere of sex. The simplest and clearest possible presentation of the underlying physical phenomena should therefore always be given first.
The physical foundation and starting point of our whole sexual life, with all its weal and woe, with all its profound agitations and emotions, are to be found in two minute organs, two small tumours, which in the adult body furnish the reproductive cells. These are, as everyone knows, in the male the two testes or testicles, hard and round, as big as a finger-joint, which produce the sperm-cells; in the female the two ovaries, in shape and size like a dried plum, which furnish the egg-cells.
These two types of organs are often grouped together under the name of Gonads, or Sexual Glands.
It is essentially the testes or the ovaries, as the case may be which determine the sexual difference, because they produce the reproductive cells and also because of the specific chemical constituents which they pour into the blood stream.
The most extraordinary thing about the testicles is that they migrate from the abdominal cavity where they are developed, in order to form a special outgrowth at the bottom of the belly. The testicles in man, like the ovaries in woman, are originally developed fairly high up in the abdominal cavity on either side of the lumbar vertebrae. But in the higher mammals and in man the testicles leave their original situation before birth and move lower and lower, like a hernia, forcing a passage right through the muscle fibres of the abdominal wall and pushing the peritoneum before them.
They never break through the skin, but at last, approaching eachother in the groins, they drop into two folds of the skin at the lower part of the body between the thighs. These folds are a continuation of the gluteal folds, and analogous to the folds which in the female form the labia majora. In the male, however, they grow together to form a single sac called the scrotum containing the testides, divided by an internal septum. The raphe in the median line of the body, where the two halves of the scrotum meet, is clearly seen even in the adult.
The two testicles are quite palpable in the scrotum, and so also is the sperm-duct (seminal canal) on each side. The latter feels like a thin hard cord. Fortunately, the two testicles hardly ever hang at the same level, otherwise they would often be squeezed together and cause pain. This is easily understood, as they had to accommodate themselves to each other even in utero.
Anteriorly, i.e., seen from in front, the scrotum is partially covered by a continuation of the urinary passage, the copulatory organ (the membrum virile or penis).
In girls, the ovaries migrate downwards a little before birth and take up a position about the level of the upper margin of the pubic bone.
Even if the descent of the testicles was originally a pathological process, it must be admitted that this migration of both testicles to the exterior of the body, is to be considered as a wholly important event in the history of evolution. Thus, these organs at once become far more accessible than previously to external and voluntary stimulation. This intensifies the male sexual life very considerably and brings it more completely into the realm of consciousness. The increased vulnerability and the possibilities of subsequent hernia which inevitably accompanied this change would certainly count little against the gigantic advantage. This is shown most clearly by the fact that in the survival of the fittest the descended testis has gained the victory, and that the higher orders with their increased sexuality have reached a higher stage of development.