ACTIVITIES OF THE MALE REPRODUCTIVE SYSTEM 31 



d. Two Types of Vertebrate Testes Relative to Sperm Formation 



The importance of the epididymal duct in many vertebrates and its relative 

 absence in others, focuses attention upon the fact that in many vertebrate 

 species sperm are produced, stored, and physiologically matured entirely 

 within the confines of the testis (frog, bowfin, stickleback, etc.). The repro- 

 ductive duct under these circumstances is used mainly for sperm transport. 

 In many other vertebrate species sperm are morphologically formed in 

 the testis and then are passed on into the accessory structures for storage and 

 physiological maturation. Functionally, therefore, two types of testes and two 

 types of accessory reproductive ducts are found among the vertebrate group 

 of animals (fig. 17). It naturally follows that the testis which produces, stores, 

 and physiologically matures sperm is best adapted for seasonal activity, par- 

 ticularly where one female is served during the reproductive activities. That 

 is, it functions as an "all at one time" spawning mechanism. On the other hand, 

 that testis which produces sperm morphologically and passes them on to a 

 tortuous epididymal duct for storage and physiological maturing is best adapted 

 for the continuous type of sperm production or for the service of several 

 females during a single seasonal period. The sperm, under these conditions, 

 pass slowly through the epididymal duct, and, therefore, may be discharged 

 intermittently. 



4. Function of the Seminal Vesicles (Vesicular Glands) 



The seminal vesicles show much diversity in their distribution among vari- 

 ous mammals. Forms like the cat, dog, opossum, rabbit, sloth, armadillo, whale, 

 do not possess them, while in man, rat, elephant, mouse, they are well- 

 developed structures. It was formerly thought that the seminal vesicles in 

 mammals acted as a storehouse for the sperm, hence the name. In reality 

 they are glandular structures which add their contents to the seminal fluid 

 during the sexual act. 



5. Function of the Prostate Gland 



The prostate gland also is a variable structure and is found entirely in the 

 marsupial and eutherian mammals. In marsupials it is confined to the pros- 

 tatic portion of the urethral wall; in man it is a rounded, bulbous structure 

 which surrounds the urethra close to the urinary bladder. In many other 

 mammals it is a much smaller and less conspicuous structure. It discharges 

 its contents into the seminal fluid during the orgasm. It is probable that the 

 prostatic and vesicular fluids form the so-called "vaginal plug" in the vagina 

 of the rat, mouse, etc. 



6. Bulbourethral (Cowper's) Glands 



The bulbourethral glands are absent in the dog but present in most other 

 mammals. In marsupials and monotremes these structures are exceptionally 



