1 Sperm maturation
Sperm maturation is defined as the development of
the ability of spermatozoa to fertilize eggs as they progress
through the epididymis. The definition was first applied
to in vivo fertilization where spermatozoa were removed
from the caput, corpus or cauda epididymidis and in-
seminated into the vagina, uterus or oviduct of different
species. The ability of spermatozoa to fertilize eggs, as
judged by the percentage of pregnant women, litter size,
percentage of fertilized eggs flushed from the oviduct or
percentage of men with patent ducts after epididymo-
vasostomy who subsequently fathered children, is always
higher when spermatozoa are obtained from the more
distal parts of the tract (Figure 1). In some early and
oft-cited work [1], the number of spermatozoa insemi-
nated was not always controlled for, so the greater num-
ber of spermatozoa obtained from the cauda might have
biased results in the direction of greater success in that
epididymal region. Later studies, with both sperm num-
bers and overall motility controlled for [2, 3], confirmed