ACTIVITIES OF THE MALE REPRODUCTIVE SYSTEM 



21 



b. Some Definitions 

 Semen or seminal fluid is the all-important substance which the male con- 

 tributes during the reproductive event. It is the product of the entire repro- 

 ductive system, including special glands of the accessory reproductive struc- 

 tures. The semen is composed of two parts: 



(1) The sperm (spermatozoa, spermia) are the formed elements which 

 take part in the actual process of fertilization. 



The seminal plasma, a fluid part, is a lymph-like substance contain- 

 ing various substances dissolved or mixed in it. These contained sub- 

 stances are important as a protection for the sperm and as an aid to 

 the process of fertilization. 



With regard to the second function of the male genital system, namely, 

 the delivery of sperm to the site of fertilization, it should be observed that 



(2) 



Fig. 10. Spermatophores of common urodeles. (Redrawn from Noble: Biology of the 

 Amphibia, New York, McGraw-Hill.) (A) Triturus viridescens. (After Smith.) (B) 

 Desmognathiis fuse us. (After Noble and Weber.) (C) Eurycea bislineata. 



in some vertebrates this is a more simple problem than in others. In those 

 forms which practice external fertilization, the male system simply discharges 

 the seminal fluid into the surrounding external medium. However, in those 

 vertebrates where internal fertilization is the rule, the female system assumes 

 some of the burden in the transport of the semen to the region where fertili- 

 zation is consummated, thus complicating the procedure. In these instances, 

 the male genital tract is called upon to produce added substances to the seminal 

 fluid which aid in protecting the sperm en route to the fertilization site. 



The elaboration of the androgenic or male sex hormone is a most impor- 

 tant function. Androgenic or male sex hormone substances are those organic 

 compounds which induce maleness, for they aid the development of the male 

 secondary sex characteristics, enhance the growth and functional development 

 of the male accessory reproductive structures, and stimulate certain aspects 

 of spermatogenesis." Like the estrogens, androgens are not confined to a 

 particular sex; they have been extracted from the urine of women and other 

 female animals. The androgens derived from urinary concentrates are andros- 



