EMBRYOLOGY. 265 



The vas deferens, the excretory duct of the testicle, is about two 

 feet in length, and may be traced upward from the epididymis to 

 the under surface of the base of the bladder, where it unites with 

 the duct of the vesicula seminalis to form the ejaculatory duct. 



The vesiculae seminales are two lobulated, pyriform bodies about 

 two inches in length, situated on the inner surface of the bladder. 



They have an external fibrous coat, a middle muscular coat, and 

 an internal mucous coat, covered by epithelium, which secretes a 

 mucous fluid. The vesiculae seminales serve as reservoirs, in which 

 the seminal fluid is temporarily stored up. 



The ejaculatory duct, about 1/4 of an inch in length, opens into 

 the urethra, and is formed by the union of the vasa deferentia and 

 the ducts of the vesiculae seminales. 



The prostate gland surrounds the posterior extremity of the 

 urethra, and opens into it by from twenty to thirty openings, the 

 orifices of the prostatic tubules. The gland secretes a fluid which 

 forms part of the semen and assists in maintaining the vitality of 

 the spermatozoa. 



Semen is a complex fluid, made up of the secretions from the 

 testicles, the vesiculae seminales, the prostatic and urethral glands. 

 It is grayish-white in color, mucilaginous in consistence, of a char- 

 acteristic odor, and somewhat heavier than water. From half a 

 dram to a dram is -ejaculated at each orgasm. 



The spermatozoa are peculiar anatomic elements, developed within 

 the seminal tubules, and possess the power of spontaneous move- 

 ment. The spermatozoa consist of a conoid head and a long, fila- 

 mentous tail, which is in continuous and active motion ; so long 

 as they remain in the vas deferens they are quiescent, but when 

 free to move in the fluid of the vesiculae seminales, they become very 

 active. 



Origin. The spermatozoa appear at the age of puberty, and are 

 then constantly formed until an advanced age. They are developed 

 from the nuclei of large, round cells contained in the anterior of 

 the seminal tubules, as many as fifteen to twenty developing in a 

 single cell. 



When the spermatozoa are introduced into the vagina, they pass 

 readily into the uterus and 'through the Fallopian tubes toward the 

 ovaries, where they remain and retain their vitality for a period 

 of from eight to ten days. 



