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.