DEVELOPMENT OF TESTES AND SCROTUM 3 



Measurements were made of the diameters of the seminiferous tubules, show- 

 ing the increase in the size of tubules that takes place during development. 

 Representative measurements are given in Table 1. 



Table 1. — Diameters of Seminiferous Tubules in the Testes of the 

 Ram at Various Ages. 



Age at Castration Diameter of Tubules 



(Days) (Micra) 



21 36.5 



42 43.5 



63 54.5 



84 64.7 



105 82.1 



126 119.7 



147 163.4 



Rapid development of the germinal epithelium in this series began at about 

 84 days of age and spermatozoa first appeared at 147 days. Photomicrographs 

 of representative sections are shown in Figures 1 to 4. 



Bull 



A study was made of nine bulls representing four breeds and ranging from 

 63 to 450 days of age. Blocks of testes were taken at the time of castration and 

 prepared for histological examination. Measurements were taken of the tubules, 

 and the average diameter at each of the nine stages is given in Table 2. 



Table 2. — Diameters of Seminiferous Tubules in the Testes of the 

 Bull at Various Ages 



Age at Castration Diameter of Tubules Breed 



(Days) (Micra) 



63 70.3 Guernsey 



65 58.0 Holstein 



88 60.6 Shorthorn 



104 72.8 Shorthorn 



142 81.9 Hereford 



181 116.1..: Hereford 



224 148.9 Hereford 



261 154.1 Hereford 



450 217.3 Shorthorn 



At 63 days the seminiferous tubules contained only a loosely arranged row of 

 spermatogonia and an occasional primary spermatocyte. The lumina were 

 filled with an opaque mass of material. Little change was observed in the next 

 three stages, except for an increase in primary spermatocytes at 104 days. 

 Rapid development of the epithelium began after the 104-day stage. At 142 

 days primary spermatocytes were present in all tubules, and at 181 days 

 secondary spermatocytes had appeared in all tubules. Spermatozoa were 

 present in many tubules at 224 and 261 days and in all tubules at 450 days. 

 After 142 days the material filling the lumina gradually disappeared, leaving a 

 rather large lumen with epithelial cells arranged in a compact layer near the 

 basement membrane. This continued until the last stage examined (450 days), 

 when the epithelial cells occupied most of the space in the tubules. 



