10 



MASS. EXPERIMENT STATION BULLETIN 331 



'Bull -bhorthorn 

 /Ige - I Of c/ays 



lj 35 30 1$ 10 10 15 50 35 57 C 



IBu II - Hereford 

 Age - Z £^ c/ays 



it 1 1 1 1 i n 1 1 1 1 1 1 ii 1 1 i ll i i i n 1 1 i n 1 1 i n 1 1 '' ' Vr 



37 35 50 15 10 £0 25 SO 35 5ft 





Bu // - Hereford 

 Age -261 c/ays 



H-H- 

 37 



II H I I M I ' I H I i i i I M I I I I I I I I I I I I H H M 

 35 30 IS 10 10 £5 30 Z5ll'C 



Figure 17. Kymograph Records Showing the Development of Sensitivity to Temperature 

 Changes in the Tunica Dartos Muscle of the Bull. 

 Records were taken on isolated muscle strips. Time is in one-minute Intervals on the 

 base line, and temperatures are recorded in °C. 



Bull 



The physiological and histological development of the tunica dartos in the 

 bull was very similar to that in the ram. The series showed more variation, 

 probably because of the variety of breeds represented. The age, breed, and 

 altitude of contraction recorded for each animal are given in Table 7. The 

 temperature at which contraction began varied so little from 36°C. that these 

 figures are omitted. 



The large contraction observed at 88 days does not fit in with the results on 

 the other younger animals. Rapid development of the germinal epithelium of 

 the testes was first observed at 142 days, and at this time the tunica dartos in 

 this animal did not show any marked sensitivity to temperature changes. 

 However, the tunica dartos showed a marked reaction to temperature changes 



