Spermatogenesis and duration of transit of spermatozoa through the excurrent ducts of stallions.

The cycle of the seminiferous epithelium was divided into eight stages on the basis of meiotic divisions, shape of the spermatid nuclei and location of the spermatids with elongated nuclei. Duration of this cycle was 12-2 days (S.E. +/- 0-1) as determined by [3H]thymidine injections and autoradiography. The life-span of primary spermatocytes was 19-0 days, secondary spermatocytes 0-7 days, spermatids with round nuclei 8-7 days, and spermatids with elongated nuclei 10-1 days. Labelled spermatozoa entered the caput epididymidis 35 days, and appeared in the ejaculate 39-9 days, after the isotope injection. The mean minimal time required for spermatozoa to pass through the excurrent ducts was 4-9 days. However, the average transit time was estimated to be between 8 and 11 days. Variation in the duration of the cycle between species is discussed.