258 The Vertebrate Organ Systems 



the tail of the epididymis, the vas deferens passes upward as part of the 

 spermatic cord. This latter structure is made up of connective tissue, 

 blood vessels, and the vas deferens. Owing to the path which the testis 

 took when migrating to the scrotum, the vas deferens loops over the 

 ureter before joining the urethra at the base of the urinary bladder. 



The Penis. — Within the penis is the urethra which serves as the 

 common passageway for the sperm and urine. Essentially, however, the 

 penis should be regarded as the copulatory organ of the male. The 

 greater bulk of the structure is made up of three cylindrical masses of 

 tissues which contain large vascular spaces. When these are filled with 

 blood, the penis becomes erect. 



The tip of the penis where the urethra opens is slightly enlarged to 

 form the glans penis. Covering this portion is the prepuce or foreskin, a 

 fold of skin which is continuous with that of the rest of the body. Within 

 this fold are small sebaceous glands which produce an odoriferous sub- 

 stance. The secretion of these glands acts as a lubricant during copula- 

 tion. 



The Glands of the Reproductive System. — Several glands are 

 associated with the male reproductive tract. Just before the junction 

 of the vas deferens with the urethra, there is a pair of saclike glands, 

 the seminal vesicles. These are lined with mucous glands. Immediately 

 below the junction of the urethra and vasa deferentia is the lobed pros- 

 tate gland which secretes a viscid alkaline fluid, the prostatic fluid. 

 Slightly below the prostate gland on either side of the urethra are two 

 very small glands, Cowper's glands, which, too, secrete a viscid fluid. 

 The secretions of these glands along with sperm form the semen. 



The semen is a grayish white, viscid fluid, containing about 

 70,000,000 sperm in a cubic centimeter. During a single ejaculation at 

 least 300,000,000 are released. The secretions of the three sets of 

 glands act as a medium for transporting the tiny sperm. Also their 

 alkalinity protects the sperm against the destructive acidity of the female 

 genital tract. 



The Sperm. — The individual human sperm (Fig. 76,B) is about 

 0.05 mm. in length, and consists of a head, middle piece, tail, and end 

 piece. The head is formed from the nuclear material of the cell from 

 which the sperm arose ; the tail gives motility to it. Each sperm passes 

 from the tubule, where it is produced, into the epididymis, where it 

 completes its development. As it passes through the ducts, cilia lining 



