As we have seen in previous lessons, Nature has as her two principal ends (1) the preservation and maintenance of the body of the individual being, in health, vigor, and normal functioning; and (2) the perpetuation and preservation of the race. The first end is served by means of the processes of vital activity, such as we have just considered; the second end is served by the processes of generation and reproduction, the system of which we shall now consider. Self-preservation and the instinct of sex and parenthood-these two constitute Nature's primal and elementary instincts; and she has built up and maintained an intricate and elaborate mechanism to serve her purposes in both of these instinctive series of processes.

The reproductive organism of the male human being is as follows: (1) The Penis; (2) the Testes; (3) the Prostate Gland; (4) the Cowper's Glands; (5) the Vesiculae Seminales, The following brief somewhat technical description gives a general idea of the characteristics and functions of each of these.

The Penis is the intromittent reproductive organ of the male; that is to say, the organ by and through which the seminal fluid is conveyed from the male to the female reproductive organism. This organ consists of erectile tissue arranged in three cylindrical compartments, each of which is surrounded by a fibrous sheath. It consists of several parts, which are called the roots, the body, and the extremity or glans penis, respectively. It is also surrounded by vessels, nerves, and skin.

The Testes, or testicles, are two glands which secrete the seminal fluid of the male. They are egg-shaped, and are suspended in the scrotum or pouch by means of the spermatic cords. A short, closely contracted scrotum is generally regarded as a sign of the health of the reproductive organism, and of the general system; while an elongated, flabby scrotum is regarded as a sign of physical depression and lack of vigor. Nature protects the testes by six separate coverings, the two outer ones of which are the muscles and skin of the scrotum. The spermatic cord is composed of arteries, veins, lymphatics, nerves, and the excretory ducts of the testes, and extend from the internal abdominal ring to the back part of the testicles which it supports in the scrotum.

The Prostate Gland is a muscular gland located in front of the neck of the bladder, and at the beginning of the urethra or canal which carries the urine from the bladder, and which in the male also carries the seminal fluid. This gland resembles a horse-chestnut in shape and size. It secretes a milky fluid which passes through the prostatic ducts into the prostatic portion of the urethra. In middle-aged men this organ sometimes becomes enlarged and troublesome, but this condition may be removed by the proper treatment.

The Cowper's Glands are two small glands, about the size of peas, situated one on each side of the membraneous portion of the urethra, close above the bulb, each gland having an excretory opening into the bulbous portion of the urethra.

The Vesiculae Seminales, or seminal vesicles, are two small pouches lying between the rectum and the base of the bladder; they serve as reservoirs for the semen, and also for another fluid which accompanies the semen in its discharge. It has two ejaculatory ducts, one on each side.

The Semen, or seminal fluid (containing the reproductive "seed") is secreted by the testes, and stored in the reservoirs of the vesiculae seminales above described. It consists of a colorless transparent fluid, in which is contained solid particles of protoplasm, namely the seminal granules and the spermatozoa. Under sexual excitement the semen is forced from the vesiculae seminales by muscular contraction, and, passing into the urethra is met by the secretions of the Cowper's Glands, and those of certain mucous follicles opening into the urethral passages; peristaltic action finally ejaculating the seminal fluid from the male organism. The spermatozoa are the essential element of the seminal fluid, the other fluids and secretions being merely accessory and secondary in function and offices.

The Spermatozoa, or male elements of reproduction, are microscopic living creatures, each resembling a minute tadpole, with head, rod-like body, and a hair-like tail which is in constant motion from side to side, the tail serving to propel the creature to its destination. In the male human being the spermatozoa each measure about one six-hundredth of an inch in length, and are present in countless numbers in the semen. They dwell in the gelatinous mass which composes a part of the seminal fluid of the male. The spermatozoa constitute the so-called "seed" of the male, which impregnates the ovum of the female, as we shall see presently.

The reproductive organism of the female human being is grouped into two classes, viz., the external organs, and the internal organs, respectively.

The external reproductive organism of the female human being is as follows: (1) The Mons Veneris, or fatty eminence in front of the pubis, above the other external organs; (2) the Labia Majora and the Labia Minora, being respectively the large and small lip-like coverings enclosing and protecting the vaginal orifice; (3) the Clitoris, a small organ hidden by the labia minora, having at its extremity a small sensitive tubercle; (4) the Meatus Urinarius, or orifice of the urethra of the female, which lies near to the vagina and about an inch below the clitoris -this, strictly speaking however, is not a reproductive organ although associated with such, as its purpose is that of serving as a passage for the urine; (5) the Vaginal Orifice is the outer entrance to the vagina, and is located just below the meatus urinarius. It is surrounded by the sphincter vaginae muscle.

The internal reproductive organism of the human female is composed of the following organs: (1) The Vagina, a canal or channel leading from the vaginal orifice to the uterus or womb, which is situated in front of the rectum and behind the bladder. It extends in an upward and backward curve of about six inches in length, and reaches and encloses the lower part of the neck of the uterus or womb. On either side of the vagina, near the orifice, are the two glands of Bartholine, which correspond closely to the Cowper's glands of the male, with excretory ducts opening upon the side of the labia minora. The vagina is lined with a" muscular coat, a layer of erectile tissue, and an internal mucous lining. It is capable of great distension in childbirth, after which it resumes its normal dimensions. The office of the vagina is to serve as a channel for the introduction of the fertilizing male seminal fluid; to sustain the weight of the uterus; to serve as a passage for the menstrual fluid; and to afford a passage for the delivery of the infant at childbirth.