## Abstract

Correlations were studied between various morphological and functional characteristics of the testis and seminal vesicle in bull calves and bulls, ranging in age from 28 days to 17$\frac{1}{2}$ years. Data obtained by the analysis of testosterone and androstenedione in the testes, and of fructose and citric acid in the seminal vesicles, were related to results of gross anatomical and histological measurements of these organs. The mean diameter of the seminiferous tubules was adopted as a means of assessing testicular function, since it was shown that this diameter is related to the weight of the testis as a whole (r = 0$\cdot $92, P < 0$\cdot $001), to the arrangement of the interstitial tissue, and to definite stages in the differentiation of the seminiferous epithelium. At 28 days, when the bull testis is relatively inactive, both as regards spermiogenesis and the endocrine function, the mean diameter of the seminiferous tubules was 48 $\mu $. At the age of 90 days, coinciding with the appearance of spermatogonia in the testes, and just prior to the marked increase in fructose and citric acid formation in the seminal vesicles, it was $\mu $. At about 4$\frac{1}{2}$ months, when the androstenedione/testosterone ratio falls abruptly, the tubular diameter increased to more than$\mu $. By 7$\frac{1}{2}$ months, when the first spermatozoa appear in the tubules, it had risen to 177 $\mu $. A significant correlation was established between the growth and secretory activity of the seminal vesicles and the diameter of the seminiferous tubules in bull testes. Correlation coefficients were established between the tubular diameter and the following: the weight of the seminal vesicles, r = 0$\cdot $95, P < 0$\cdot $001; the contents of fructose and citric acid in the seminal vesicles, r = 0.81, P =0.01 to 0.001; and the concentrations of fructose and citric acid in the seminal vesicles, r = 0.82 and r = 0.76, respectively, P = 0.01 to 0.001.