Rabbit spermatozoa were removed from various levels of the male reproductive tract. They were examined in Hanks' solution at room temperature with a phase contrast microscope and their motility characteristics were recorded cinematographically.
Spermatozoa from the seminiferous tubules and ductuli efferentes show weak, vibratory movements with no forward progress. Little change in motility occurs until the sperm reach the flexure of the caput epididymidis where some are capable of moving more vigorously in a circular fashion. Samples from the distal caput epididymidis show a sudden increase in sperm activity and a consistent pattern of tight, circular movement. As the sperm traverse the corpus epididymidis, increasing numbers show progressive, forward movement with longitudinal rotation. The proportion of such sperm becomes significant only in samples from the upper cauda epididymidis and more distal regions. Sperm from the ductus deferens rarely retain the circular movement.
It is concluded that rabbit spermatozoa undergo a distinct sequence of changes in their swimming movements as they mature in the epididymis. A similar change was noted in epididymal spermatozoa from the rat and guinea pig suggesting that this process is fundamental to sperm maturation in several species.