6 MASS. EXPERIMENT STATION BULLETIN 331 



The rapid development of the germinal epithelium, then, began at about 142 

 days in this series, and spermatozoa first appeared at 224 days. Photomicro- 

 graphs of representative sections taken from this series are shown in Figures 

 5 to 8. 



Boar 



Eight boars (Chester Whites and Berkshires) were castrated at ages ranging 

 from 12 to 147 days. Blocks of testes were taken and prepared for histological 

 examination. The ages of all the boars and the diameters of the tubules at 

 each age are given in Table 3. 



Table 3. — Diameters of Seminiferous Tubules in the Testes of the 

 Boar at Various Ages 



Age of Castration Diameter of Tubules 



(Days) (Micra) 



12 51.6 



21 50.9 



42 56.7 



61 62.5 



84 59.3 



105 83.8 



126 139.9 



147 165.7 



Little development of the germinal epithelium was observed until after 84 

 days of age. The spermatogonia were arranged in a loose layer on the basement 

 membranes at 12 days and the remainder of each tubule was filled with an 

 opaque mass. In the succeeding stages the spermatogonia became arranged in 

 a compact and orderly fashion around the basement membrane and primary 

 spermatocytes gradually appeared, so that a few were present in all tubules at 

 84 days of age. In the 105-day stage secondary spermatocytes had appeared 

 in some tubules, and at 126 days the epithelium appeared completely organized 

 except for spermatozoa. Spermatozoa were present in some tubules at 147 

 days. 



It would seem from this series of animals that the testes of the boar develop 

 slowly up to about 84 days of age, and that after this age a more rapid develop- 

 ment sets in, with spermatozoa first being produced at about 147 days. Photo- 

 micrographs of sections from three of the boars in this series are shown in 

 Figures 9 to 11. 



Boar — Low Nutrition Series 



Five boar pigs were fed from weaning age (6 weeks') on a very low plane of 

 nutrition. These pigs were castrated at from 84 to 168 days of age. As shown 

 in Table 4, the gains made in body weight were low when compared with the 

 gains of the normal group described above, some of which were used for controls. 



