ACTIVITIES OF THE MALE REPRODUCTIVE SYSTEM 27 



The testis, however, is not the only site of androgen formation. As men- 

 tioned above, androgens are found in the urine of female animals, castrates, 

 etc. It seems probable that the suprarenal (adrenal) cortex may secrete a 

 certain androgenic substance, possibly adrenosterone, a weak androgen. Many 

 androgens have been synthesized also in the laboratory (Schwenk, '44). 



2) Biological Effects of the Male Sex Hormone. The presence of the male 

 sex hormone in the male arouses the functional development of the accessory 

 reproductive structures, the secondary sexual characters, and also stimulates 

 the development of the seminiferous tubules. 



a) Effects upon the Accessory Reproductive Structures. Castra- 

 tion or removal of the testes from an animal possessing a continuous type 

 of testicular activity produces shrinkage, and a general tendency toward atro- 

 phy, of the entire accessory reproductive structures. Injection of testosterone 

 or other androgens under such conditions occasions a resurgence of func- 

 tional development and enlargement of the accessory structures (fig. 16). 

 Moreover, continued injections of the androgen will maintain the accessories 

 in this functional state (Moore, '42; Dorfman in Pincus and Thimann, '50). 

 Similarly, under normal conditions in those vertebrates which possess the 

 seasonal type of testicular function, the accessory reproductive organs shrink 

 in size with a loss of functional activity when the testis undergoes regression 

 during the period immediately following the active season. An enlargement 

 and acquisition of a normal functional condition of the accessories follows 

 testicular development as the breeding season again approaches (Bishop, '42; 

 Wislocki, '43; Matthews, '38; Turner, C. L., '19). (Compare figs. 12A-D.) 



b) Effects upon Secondary Sex Characteristics and Behavior of 

 THE Individual. In addition to the primary effects upon the reproductive 

 system itself, the androgens induce many other secondary structures and altera- 

 tions of the physiology and behavior of the individual. The influence of the 

 testicular hormone has been demonstrated in all of the vertebrate groups 

 from fishes to mammals (Dorfman in Pincus and Thimann, '50). Examples 

 of testosterone stimulation are: the singing and plumage of the male bird; 

 hair development of certain mammals; the crowing and fighting, together 

 with spur, comb, and wattle growth in the rooster. The disagreeable bellig- 

 erency and positive energy drive of the bull, stallion, or human male may 

 be attributed, largely, to the action of testicular hormone. However, lest we 

 disparage this aggressive demeanor unduly, it should be recognized that upon 

 such explosive force rests the preservation of species and races in some in- 

 stances. As an example, witness that hairy dynamo of the barren northern 

 tundras, the bull muskox, whose fiery pugnaciousness when the need arises 

 undoubtedly has been a strong factor in the preservation of this species. 



An excellent example of the effect of testosterone is shown in the develop- 

 ment of antlers and change in behavior of the Virginia deer, Odocoileus vir- 

 ginianus borealis (Wislocki, '43). In the northern climate, the testes and male 



