16 MASS. EXPERIMENT STATION BULLETIN 331 



One other point is of interest here. The tunica dartos of the 126-day-old 

 boar in the low-nutrition group showed the most marked reaction to tempera- 

 ture changes. This boar also showed marked development of the germinal 

 epithelium as compared to that of the other animals on low nutrition. There 

 is an indication here that the testicular hormone or the fraction of it responsible 

 for the development of the tunica dartos may be elaborated by the germinal 

 epithelium. It will be remembered, also, that in the normal animals the first 

 marked activity of the tunica dartos and that of the germinal epithelium are 

 closely associated. 



SUMMARY 



The work reported in this bulletin was concerned with the development of 

 the testes and of the tunica dartos muscle in the scrotum of the ram, the boar, 

 and the bull. The experimental results may be summarized briefly as follows: 



1. Marked development of the germinal epithelium was first noted at 84 

 days of age in the ram, 142 days in the bull, and 84 days in the boar. 



2. Spermatozoa first appeared in the normal series at 147 days in the ram, 

 224 days in the bull and 147 in the boar. 



3. With hoars, a low plane of nutrition resulted in a considerable retardation 

 of development of the testes as measured by testicular volume, diameter of the 

 seminiferous tubules, and development of the germinal epithelium (with one 

 notable exception). 



4. The tunica dartos muscle first showed a marked reaction to temperature 

 changes at from 63 to 84 days in the ram and at 105 days in the boar. Results 

 with the bull were somewhat variable. 



5. Studies of the effect of castration and injections of testicular hormone 

 indicate that, in the ram, the tunica dartos is dependent upon a testicular 

 hormone for the development and maintenance of its reactivity to tempera- 

 ture changes. 



6. Weight of the testes does not appear to be a factor in the development of 

 the temperature-regulating mechanism of the scrotum. 



7. Low nutrition in the boar resulted in a retarding of the development of 

 the tunica dartos muscle. It seems possible that this is an indirect effect re- 

 sulting from a retarding of development of the testes. 



8. The evidence presented seems to indicate that the tunica dartos muscle 

 is dependent upon a testicular hormone for the development and maintenance 

 of its sensitivity to temperature changes. 



Publication op this Document Approved by Commission on Administration and Finance 

 3m — 5-'36. No. 7772. 



