8 MASS. EXPERIMENT STATION BULLETIN 331 



Ram 



Fourteen ram lambs varying in age from 21 to 189 days were used. Records 

 of the reaction of isolated strips of the tunica dartos muscle to temperature 

 changes were obtained as described above. Measurements were then made to 

 determine the altitude of the contractions and the temperature to which it was 

 necessary to lower the fluid surrounding the strip of muscle before it began to 

 contract. These records for each animal are given in Table 6. 



It may be noted that up to 64 days only small contractions occurred, but 

 that all strips from rams 64 days of age or over (with one exception, 70 days) 

 showed a marked reaction to the temperature changes to which they were sub- 

 jected. The temperatures at which the muscles began to contract ranged from 

 30° to 34 C C. up to 63 days, but in all the older stages contraction began at from 

 35° to 37°C, indicating that the muscle becomes more sensitive to temperature 

 changes as the animal matures. Four representative records are shown in 

 Figure 16. 



The histological changes which occur as the tunica dartos develops consist 

 chiefly of an increase in the relative and total amount of smooth muscle fibers 

 and a decrease in the relative amount of connective tissue. Most of the strands 

 of smooth muscle follow the long axis of the scrotum, but some on the inner 

 surface run at oblique and right angles. The strands anastomose frequently and 

 in the earlier stages are interspersed with large amounts of connective tissue. 

 As the animal grows older the muscle becomes thicker, the strands of smooth 

 muscle become larger and tend to join together to make larger strands, and 

 relatively less connective tissue is present between the strands. Photomicro- 

 graphs of representative sections are shown in Figures 18 to 20. 



It is interesting to note that the age at which the tunica dartos became 

 markedly sensitive to temperatures changes (63 to 84 days) was approximately 

 the same as the age (84 days) at which rapid development of the germinal 

 epithelium was first observed. 



