MAMMALIAN TESTIS 



309 



weight of the testis in primates have been 

 supplied by hunting and scientific expedi- 

 tions. Schultz (1938) studied 87 adult pri- 

 mates. The relative testicular weights (tes- 

 ticular weight divided by body weight X 

 100) varied between 0.1 and 0.4 in Ameri- 

 can monkeys. Considerably more variation 

 was seen in Old World monkeys. The rela- 

 tive weight in five species of macaques 

 varied between 0.46 and 0.92, but in langurs 

 was only 0.06. The weight ratio in the orang- 

 utan was 0.05, in the gibbon and man 0.08, 

 and in the chimpanzee, 0.27. Rough estima- 

 tions of the ratio of the volume of interstitial 

 tissue to tubular volume showed that the 

 macacjue has a greater relative volume of 

 interstitial tissue than man. Testicular 

 weights vary according to race; Japanese 

 men have smaller testes than American men 

 (Schonfeld, 1943) . 



The human testis at birth consists of 

 small tubules measuring 50 to 75 yn in di- 

 ameter and arranged in cords containing 

 several rows of darkly staining nuclei. The 

 epithelium is mostly undifferentiated, but 

 large cells with sharp boundaries are pres- 

 ent. These are primary germ cells. The 

 interstitium of the testis is highly developed 

 and contains solidly packed Leydig cells. 

 After birth the Leydig cells disappear from 

 the interstitium in a matter of a few weeks. 

 From this time, the testis remains generally 

 quiescent until puberty, when Leydig cells 

 reappear as a result of the secretion of 

 gonadotrophin. Only mesenchymal cells re- 

 sembling fibroblasts characterize the in- 

 terstitium in the period from a few weeks 

 after birth until puberty. The germinal 

 cords acquire a lumen at approximately 6 

 years of age, although this landmark shows 

 considerable variation. The nuclei of the 

 germinal cells at this time are arranged in 

 two layers. 



At puberty, which may occur at any age 

 from 9 to 19 years, a great increase in size 

 and tortuosity of the tubules occurs. The 

 lamina propria develops, the Sertoli cells 

 become differentiated, and the seminiferous 

 epithelium gradually matures. The Leydig 

 cells mature somewhat later than the 

 changes noted in the tubules and become 

 characteristically arranged in groups in 

 the intertubular zones. 



After maturity is attained, the adult his- 



tologic pattern may be maintained into old 

 age without pronounced changes. Spermato- 

 genic activity varies from tubule to tubule, 

 but an over-all picture shows spermatogene- 

 sis proceeding in an orderly fashion, with 

 sperm heads closely approximating the lu- 

 minal end of the Sertoli cells. About two- 

 thirds of the tubule is occupied by the 

 germinal epithelium. The lumen makes up 

 about 15 per cent of the tubule. The pro- 

 portionate volumes for the germinal cells 

 are as follows: spermatogonia, 24 per cent; 

 spermatocytes, 45 per cent; spermatids and 

 spermatozoa, 29 per cent; various abnormal 

 cells, 2 per cent. The Sertoli cells occupy 

 about one third of the tubular epithelium. 

 The Leydig cells occupy 9 per cent of the 

 total intertubular spaces. About 66 per cent 

 of the human adult testis is composed of 

 tubules and about 22 per cent is made up of 

 the intertubular spaces (Table 5.1). With 

 age, progressive fibrosis occurs in the human 

 testis, the width of the tubular wall in- 

 creases, and thinning of the germinal epi- 

 thelium occurs (SnifTen, 1952; Charny, 

 Constin and Meranze, 1952; Albert, Under- 

 dahl, Greene and Lorenz, 1953b; de la 

 Baize, Bur, Scarpa-Smith and Irazu, 1954; 

 Roosen-Runge, 1956). 



III. Descent of the Testis 



The descent of the testis from an ab- 

 dominal position in the fetus was known to 

 the ancients (Badenoch, 1945). This change 

 in position is a mammalian phenomenon. In 

 the Monotremata and most of the Edentata, 

 the testes are abdominal. Some of the In- 

 sectivora, Cetacea, and Sirenia also have 

 abdominal testes. The testes in marsupials 

 lie suprapubically in a pouch that has a 

 closed vaginal process. The testes of Aplo- 

 dontia rufa, the most primitive rodent ex- 

 tant, occupy a semiscrotal position during 

 the breeding season; otherwise, the testes 

 are abdominal (Pfeiffer, 1956). In some ro- 

 dents, Lnsectivora and Chiroptera, the testes 

 are intra-abdominal in the resting stage, 

 but during the rutting season they are pulled 

 into the scrotum by muscles. In the Ungu- 

 lata. Carnivora, and Primates, the testes 

 are extra-abdominal. Exceptions are the 

 elephant and stag, whose testes are retracted 

 in the nonrutting season. Thus, "cryptor- 

 chism" is normal for many mammals, and 



