The spermatozoön is divided into three parts, the head, which is the modified nucleus of the male reproductive cell, the intermediate segment, which is the cytoplasm of the cell, and the tail, which is a veritable vibrating cilium, as found in ciliated epithelial cells.
CUT XXXI.
Spermatozoön.
a, head; b, intermediate segment; c, tail.
The spermatozoa soon detach themselves from the spermatoblasts and wander into the seminiferous tubules toward the rete vasculosum and epididymis. The spermatozoa possess their own motion. The head is propelled forward by a whip-like wriggling of the tail. The rate of movement is 1.2 to 3.6 millimeters a minute. Water checks the movement and causes the tail to curl up. Concentrated solutions of salts, sugar, albumen and urea may revive the spermatozoa to former activity. Metal salts and acids arrest the movements, while caustic potash and soda invigorate them. Even thin and weak acid solutions, as urine and the vaginal contents,[C] are harmful, while alkaline solutions are favorable to the spermatozoa. In spermatozoa, which have died gradually after ejaculation, the tail is outstretched or slightly curved, while in those discharged dead, the tail is rolled up in a spiral.
Seminal vesicles.—The seminal vesicles have several functions. The internal secretions serve directly as an excitans of the sexual impulse. The distension of the vesicles reflectorily stimulates the sexual centres. It is a well-known fact that the distention of the vesicles in strict continence gives rise to frequent erections, just as well as the full bladder, constipation, lithiasis, and diseases of the prostate or of the rectum.
The main functions of the vesicles are three in number. The vesicles serve, in the first place, as a reservoir for the testicular secretions. The other function consists in the reabsorption of the unejaculated sperma. The third function is to furnish a fluid for the dilution of the very thick testicular secretion and a medium where the spermatozoa can best carry out their motions.
The seminal vesicles secrete a peculiar mucus, which is thick, fibrinous, glairy, and albuminous. This secretion constitutes the bulk of the semen.
Prostate.—The prostatic gland has a double function. It is the main point wherefrom the stimuli for the sexual impulse start. The internal secretions of the prostatic parenchyma send libidinogenous substances into the blood. The colliculus, rich in nervous elements, sends also out nervous libidinogenous stimuli. The principal function of the prostate is its secretion which imparts to the otherwise sluggish spermatozoa their lively movements.
The secretion of the prostate is thin, milky, translucent, amphoteric or slightly acid. It contains the base spermin which causes the peculiar seminal odor. The secretion gives to the inert spermatozoa their peculiar motion and life.