The Penis is the principal generative organ of man. It is usually from five to seven inches in length, hanging pendant, and extending from the Pelvic Bones to the glans at the end, and is divided into two parts called the Cavernosum and the Spongiosum. There is a groove underneath and between these two parts, through which runs the Urethra, or urinal passage. The head of the Penis is called the Bulb, and is of a spongy nature, being filled with little cells or cavities communicating with each other, and which extend into blood vessels which run the whole length of the organ, and are finally connected with an artery and a vein in the body. When no excitement of the part exists, these cells and blood vessels are nearly empty; but when excited by sexual desires, they rapidly fill with blood, when the Penis stands erect and enlarges to one-third greater size. The erection is also assisted by a number of muscles which only act when the blood rushes into the part. These are called the Cavernosus Muscles. In some persons the erection is very sudden, while in others it is the reverse—all depending upon the temperament and construction of the parts. The time for the erection to subside is also different in different persons. The causes of this difference depend upon certain vital actions of the blood vessels not fully understood. In old age this organ will often become hard and erect, though it requires more time, and the erection subsides almost instantly after connection with a female. The Penis is often destroyed by accident or by disease, and sometimes it is naturally deformed. A case is stated by Dr. Hollick of a young man 19 years old, whose Penis was only a quarter of an inch long! By a protracted and careful course of treatment, however, it was made to grow several inches. Some male children have been born with no Penis at all—a slight swelling, like the top of a small tumor, being the only mark of the spot where it ought to have grown. In some cases of deformity like this, men have been known to beget children, the flow of Semen being ample; and it only requiring, for the purpose of impregnation, that the Semen shall be placed within the external lips of the private parts of the female, as will be shown hereafter.