MAMMALIAN TESTIS 



30; 



endocrine system in basic and clinical prob- 

 lems of the testis. The inherited types of 

 infertility in males seem to be an especially 

 rewarding field of investigation. Spontane- 

 ous tumors of the testis supply interesting 

 and instructive material for study in both 

 clinical and veterinary medicine. Tumors 

 induced in the testis by experimental means 

 have contributed nothing unique to the 

 problem of oncogenesis. They have, how- 

 ever, provided material for the concept of 

 ''hormonal dependence" of certain tumors; 

 therefore, they are of importance in the field 

 of cancer. 



Not included in this review are studies on 

 the effects of nutritional deficiency, of radia- 

 tion, and toxic substances on the testis. 

 The first is discussed in detail in the chapter 

 by Leathern. The second has been purposely 

 omitted because it belongs more to the 

 sphere of interest of the radiation biologist 

 than to that of the endocrinologist. It must 

 not be forgotten, however, that knowledge 

 of the relative sensitivity of the various 

 cells of the testis to injury, the first quanti- 

 tative information on the spermatogenic 

 cycle, and the mechanism of repopulation of 

 the germinal epithelium after severe damage 

 were contributions of the radiation biologist. 

 The third is a hodgepodge of material which 

 at present defies orderly condensation. De- 

 spite this, some of the studies in this area 

 are of potential value in providing unique 

 experimental preparations, i.e., animals with 

 testes containing only Leydig cells, or only 

 Sertoli cells. Finally, a miscellany of papers 

 dealing with the general physiology or with 

 the general biochemistry of the testis has 

 also been omitted. 



II. Postnatal Development 

 of the Testis 



In the past 20 years, voluminous descrip- 

 tive information has been compiled on the 

 events and consequences of the postnatal de- 

 velopment of the testis of mammals. Only 

 a few examples will be given. The develop- 

 mental anatomy and postnatal changes in 

 the testis of the laboratory rat have been 

 described. Various monographs on the rat 

 (Farris and Griffith, 1949, for references) 

 and Moore's chapter in the 1939 edition are 

 available. 



The testis of the guinea pig has a growth 

 spurt about the 20th day of life. The ac- 

 cessory sex structures, such as the vas defe- 

 rens, epididymis, and prostate, are stimu- 

 lated somewhat later, at 30 to 40 days. The 

 growth of these accessory organs is an in- 

 dication of male hormone activity. The 

 time at which hormonal secretion occurs 

 varies among individual animals. Varia- 

 bility (48 to 70 days) occurs also in the ap- 

 pearance of sperm (Sayles, 1939). Under 

 controlled conditions of breeding, Webster 

 and Young (1951) observed that the first 

 intromission in guinea pigs occurs at about 

 54 days of age. The first ejaculate occurs 

 some 10 days later and is sterile. Fertile 

 ejaculates begin on the average at 82 days 

 of age. Thus, a period of adolescent sterility 

 exists as the result of both lack of ejacula- 

 tion and a period when there is an in- 

 sufficiency of spermatozoa. The hamster 

 (Bond, 1945) copulates at 30 days of age 

 but is not fertile until 43 days of age. Ado- 

 lescent sterility of the male may be a more 

 common phenomenon than is generally ap- 

 jireciated. 



Tile testes of the cat are descended at 

 bh-th. Testicular growth is slow, the com- 

 bined weight of the two testes increasing 

 from 20 mg. at birth to 100 mg. at weaning. 

 During the 2 months following weaning, the 

 testes attain a weight of 130 mg. A spurt 

 in growth occurs between the third and the 

 fifth month of life, when the testes may 

 weigh 500 mg. This spurt is associated with 

 the appearance of Leydig cells and an in- 

 crease in the size of the epididymis. Mitotic 

 activity of the germinal epithelium is pres- 

 ent in testes weighing 400 to 500 mg. Sper- 

 matids appear when the testes weigh 700 

 mg., and sperm are found fairly uniformly 

 when the testes are more than 1 gm. in 

 weight. At this stage, the tubular diameter 

 is maximal. After maturity, the weight of 

 the testes is generally proportional to body 

 weight. A 5-kg. cat will have testes weighing 

 4 gm. (Scott and Scott, 1957). 



From birth to 80 days of age, the testes 

 of goats grow at a slow but uniform rate. 

 In the immature animal, the tubules are 

 small, measuring 30 fjL in diameter, and are 

 composed of a single layer of cells without 

 any lumen. The interstitial tissue contains 

 only mesenchymal cells. At 90 days of age, 



