RAT, A REPRESENTATIVE MAMMAL 145 



mature. With a microscope it is possible to study the different 

 stages of spermatogenesis in the epithelial walls of these tubules. 

 The spermatozoa of the rat are somewhat the shape of diminutive 

 harpoons with a head, middle piece, and tail. 



The vas deferens leaves the scrotum along with the nerve, artery, 

 and vein as the spermatic cord. It passes through the inguinal canal, 

 then looping anteriorly and dorsally, to pass dorsal to the ureter 

 and return posteriorly to join the urethra (tube from bladder to 

 exterior). The seminal vesicle (vesicular gland) is a conspicuous 

 sac which joins the vas deferens near its point of entrance into the 

 urethra. The seminal vesicle probably does not store spermatozoa 

 in the rat but is thought to produce an alkaline solution which is 

 mixed with the sperm. Partially surrounding the urethra at this 

 point and also on the ventral side of the urinary bladder is the 

 prostate gland. Both parts of this gland empty into the urethra. 

 It has been suggested that their secretion assists in the locomotion 

 of spermatozoa as well as their nourishment in rodents. The urethra 

 leads on through the length of the penis as a common excretory and 

 reproductive canal and ends in a slit in the end of the glans. 



Rats are sexually mature at two or three months of age. Ovulation 

 (discharge of mature ova from the ovary) occurs at intervals of 

 about three weeks after maturity in the female, except during preg- 

 nancy. This continues until the age of 15-18 months, when ovulation 

 ceases. The stoppage of sexual activity at this time is known as 

 menopause. 



References 



Adams, L. A.: An Introduction to the Vertebrates (Chap, on Mammals), New- 

 York, 1938, John Wiley & Sons, Inc. 



Greene, Eunice C. : Anatomy of the Eat, Transactions of the American Philo- 

 sophical Society, New Series, Vol. XXVII, 1935, Philadelphia. 



Hunt, H. R. : Laboratory Manual of the x\natomy of the Eat, New York, 1924, 

 The Macmillan Company. 



Metcalf, Z. P.: An Introduction to Zoology, Springfield, 111., 1932, Charles C. 

 Thomas. 



Stuart, Eichard E.: Anatomv of White Eat, Chicago, 1947, Denoyer-Geppert 

 Co. 



