Morphometry of the epididymis of the tammar wallaby, Macropus eugenii, and estimation of some physiological parameters.

About 14 ductuli efferentes (mean length 48 cm) leave the testis of the tammar. The caput, corpus and cauda epididymidis constitute 37%, 42% and 21% respectively of the total length of the ductus epididymidis (estimated to be 34.9 m long). The initial segments of the ductus epididymidis are longer, relative to body or testis mass, in the tammar than in eutherian mammals such as the rat. The main morphometric features of the male excurrent duct system of the tammar are a high ratio of surface area of luminal border:luminal volume of the ductuli efferentes (which reabsorb most of the fluid leaving the testis), a high ratio of epithelial volume:luminal volume in the caput and corpus epididymidis (which are involved in sperm maturation) and a low ratio of epithelial volume:luminal volume in the cauda epididymidis (which is involved in sperm storage). Estimates of fluid reabsorption by the ductuli efferentes and protein secretion by the caput epididymidis were respectively 8.9 microL cm-2h-1 and 2.8 micrograms cm-2h-1. Other estimates for the ductuli efferentes, caput, corpus and cauda epididymidis respectively were: sperm velocity (4.5, 4.8, 2.2, and 0.9 mm min-1), duration of sperm transit (107 min, 1.9 days, 4.7 days, and 6.3 days), total number of spermatozoa (4950 x 10(6)) and distribution of extragonadal spermatozoa (0.6, 14, 36 and 49% of the total). The values are within the ranges estimated for eutherian mammals.