The genito-urinary surface is the smallest of the surfaces. In the male (Fig. 8,--27, 28, 30) this communicates with the general external surface by the small opening at the extremity of the penis, and in the female by the opening into the vagina. In its entirety it consists in a surface of wide extent, comprising in the male the urethra, a long canal which opens into the bladder, and is continuous with ducts that lead into the genital glands or testicles. The internal surface of the bladder is extended by means of two long tubes, the ureters, into the kidneys, and receives the fluid formed in these organs. In the female (Fig 9) there is a shallow external orifice which is continued into the bladder by a short canal, the urethra, the remaining urinary surface being the same as in the male; the external opening also is extended into the short, wide tube of the vagina, which is continuous with the canal of the uterus. This canal is continued on both sides into the Fallopian tubes or oviducts. There is thus in the female a more complete separation of the urinary and the genital surfaces than in the male. Practically all of the waste material of the body which results from cell activity and is passed from the cells into the fluid about them is brought by the blood to the kidneys, and removed by these from the blood, leaving the body as urine. [Illustration: FIG. 8.--A LONGITUDINAL SECTION THROUGH THE MIDDLE OF THE BODY SHOWING THE EXTERNAL AND INTERNAL SURFACES AND THE ORGANS.