_Ejaculation._—The last important step of the male sexual act is ejaculation. The spermatozoa leave the lining of the tubuli contorti and wander through the tubuli recti to the rete vasculosum and hence through the vasa efferentia to the head of the epididymis. They continue their wanderings through the epididymis and vasa deferentia until they reach the seminal vesicles and the ejaculatory ducts. During sexual tranquility and in a normal state of health, the ejaculatory ducts, owing to the narrowness of their diameter and the oblique direction of their orifices, are sufficiently compressed to prevent the semen from reaching the urethra. The semen, therefore, remains in the seminal vesicles until needed for ejaculation. If not needed in due time, it is, as a rule, reabsorbed, and the overflow, if there be any, is discharged during sleep, accompanied by libidinous dreams. Coincident with erection the entire situation changes. Before ejaculation the testicles are forcibly drawn up to the external rings of the inguinal canal, by the action of the cremaster muscle. Through the contraction of the epididymis and the coni vasculosi, the seminal fluid is propelled toward the vasa deferentia. Through the peristaltic movement of the vasa deferentia and the seminal vesicles, the semen is pressed into the ejaculatory ducts. The latter, by means of the muscular layer in their walls, forward the semen to the prostatic urethra. The action of the ducts is at this moment facilitated by the changed direction of their orifices. The change takes place through the turgescence of the colliculus. The swelling of the colliculus and the contraction of the external sphincter of the bladder prevent the semen from flowing backward into the bladder. At this stage the muscular substance of the prostate contracts and squeezes out the prostatic fluid into the urethra. The fluid had been stowed up in the follicles until there was a demand for it. All these secretions of the testicles, seminal vesicles, and prostate, meet synchronously in the prostatic urethra and are there temporarily stowed up.