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Summary.

Groups of rats were assigned respectively to one of six unilateral surgical treatments: scrotal sham operation, scrotal vasectomy without ligation, scrotal vasectomy with ligation, abdominal sham operation, abdominal vasectomy without ligation, and abdominal vasectomy with ligation. Three months later, the mean testis weight was unaffected by the various operative procedures, but the variance of testis weight was greater following vasectomy with ligation of the ductus deferens and after operations involving the abdominal approach. Mean testicular sperm concentrations were similar in all groups, but variance of this parameter was increased after abdominal operations. While vasectomy appears to be relatively harmless, certain procedures, such as abdominal vasectomy with ligation, disturb the rat testis more than others.

Summary. By 3 months after surgery, testicular weights were 12–14% below control values in a large series of vasectomized rats of the inbred Lewis strain. Testicular sperm concentrations in the vasectomized rats were 25–29% below those in the sham-operated animals. Although modest in magnitude, these differences were highly significant (P < 0·001). Histometric analysis of testes from a smaller series of vasectomized Lewis rats revealed various proportions of abnormal seminiferous tubules. The degenerative changes included reduction in tubule diameter, fusion of spermatids, and depletion of advanced germinal elements. In the most severely affected tubules, leakiness of the blood–testis barrier was indicated by penetration of lanthanum through Sertoli-cell tight junctions.

Summary.

The reproductive activity of territorial and bachelor impala was compared. Mean bulbourethral gland weights and plasma testosterone levels were significantly higher in territorial males and were approximately twice that observed in bachelor males. The other parameters measured were similar in both social classes. The high testosterone levels in territorial males were probably a result of their territorial status and consequent sexual activity rather than a cause of it.

Summary. The weight of the skinned phallus and the diameter of its shaft and glans did not differ significantly in the two sexes of spotted hyaena, but phallus length was greater in males. The urethra of the penis was surrounded by corpus spongiosum, while the urogenital canal of the clitoris was suspended beneath the erectile bodies in loose connective tissue, an arrangement compatible with dilatation of the canal during copulation and parturition. The average width of the phallic meatus in juvenile females exceeded that in males of any age and, in adults, the clitoridal meatus was >10 times the width of the penile meatus. A robust retractor muscle situated dorsal to the urogenital canal further distinguished the clitoris from the penis; this muscle may play an important role in facilitating copulation.

Summary. Age-related changes in daily sperm production (DSP) and testicular weights were investigated in paired testes from 89 men aged 21–50 years and 43 men aged 51–80 years. For both DSP/testis and DSP/g parenchyma, remarkably large standard deviations exceeded 50% of mean values. However, DSP/g and DSP/testis for both right and left testes were approximately 30% higher in the younger than in the older group (P < 0·01) and were negatively correlated with age (P < 0·01) when data from both groups were pooled. Weights of whole testes and of testicular parenchyma were similar in both age groups and were not significantly correlated with age. However, testicular tunic weights were 29% higher in the older group (P< 0·001) and were positively correlated with age (P < 0·001). Both testicular tunic weight and the % of total testis occupied by tunic were negatively correlated with DSP/g (P < 0·01); these correlations were weakened by removing the effect of age. Although total testicular weight and testicular parenchymal weight did not change with age, these values were about 10% lower on the left than on the right (P < 0·001). In addition to its increase with age, testicular tunic weight was about 8% greater for right than for left testes in all men (P < 0·001). Although the average size of the testis varied from right to left, DSP/g was similar in paired testes (P = 0·15), and the correlation between right and left DSP/g was high (p = +0·89, P < 0·001). Much of the variation in daily sperm production in men remains unexplained. However, sperm production does decline significantly with age in the human male.