DEVELOPMENT OF TESTES AND SCROTUM 11 



at 224 and 261 days of age, the first two stages in which spermatozoa were ob- 

 served in the seminiferous tubules. Three records from the series are shown 

 in Figure 17. 



Table 7. — The Development of Sensitivity to Temperature Changes 

 in the Tunica Dartos op the Bull. 



Age at Castration Altitude of Contraction Breed 



(Days) (mm.) 



63 2.0 Guernsey 



65 . 5 Holstein 



88 27 . 5 Shorthorn 



104 11.0 Shorthorn 



142 7.0 Hereford 



181 1.0 Hereford 



224 23.0 Hereford 



261 24.5 Hereford 



The histological development of the tunica dartos muscle is a gradual process 

 similar to that in the ram. The smooth muscle strands gradually become more 

 prominent as the animal becomes older, but the older stages have considerably 

 more connective tissue between the muscle strands than is found in the ram. 

 Representative stages are shown in Figures 21 to 23. 



Boar 



The development of the tunica dartos in the boar closely parallels that in the 

 ram and bull. Therefore, detailed data are not presented. Of the nine stages 

 studied, ranging from 12 to 147 days of age, only the three oldest (105, 126, 

 and 147 days) gave a marked reaction to temperature changes. These last 

 three stages were also the ones in which rapid development of the germinal 

 epithelium took place. Some representative records of the reactions to tem- 

 perature changes are shown in Figure 27. 



The histological changes are similar to those described for the ram. Repre- 

 sentative sections are shown in Figures 24 to 26. 



FACTORS AFFECTING THE DEVELOPMENT OF THE 

 TUNICA DARTOS MUSCLE 



The fact that the tunica dartos becomes sensitive to temperature changes 

 at about the time when rapid development of the germinal epithelium begins in 

 the ram and boar, and by the time spermatozoa are produced in the bull, would 

 seem to indicate a relationship between the development of the testes and that 

 of the tunica dartos muscle. Results submitted below support this theory. 



Castration 



Seven of the rams used in studying normal development of the scrotum were 

 retained and strips of the tunica dartos obtained at various intervals after 

 castration. These strips were subjected to temperature changes and the re- 

 action of the strips recorded on a kymograph. The altitude of contractions 

 and the temperatures at which contractions began are given in Table 8, along 

 with records of these rams at the time of castration. 



