54
OBSERVATIONS ON SPERM DEVELOPMENT
[Vol. XX, Part I,
and compact and firmly adherent when situated at the anterior end of the connect-
ing piece and gets smaller, less compact and loose as it goes down the connecting
piece. The connecting piece is normal in appearance when the drop is at the posterior
end. It also appears that the function of the drop is completed when it reaches
the posterior end of the connecting piece and is no longer needed by the sperm.
In preparations from the testis, the epididymis and the ejaculate, the vast majo-
rity of the sperm are seen to possess at the anterior end of the head a cytoplasmic
cap in all the three species. Using Weigert's iron haematoxylin and safranin,
this cap takes a cytoplasmic stain, while the head takes a nuclear stain. This cap
is probably a cytoplasmic remnant and its persistence throughout the development
and even after the maturation of sperm suggests that it might be differentiated for
some specific function. Recent work [Johnston and Mixner, 1948] points to the
bull spermatozoa as capable of secreting the enzyme hyaluronidaze, which has been
demonstrated to be capable of dispersing the corona radiata cells of the ovulated
mammalian ovum. It is possible, as suggested by Rao and Hart [1948a] that this
cytoplasmic cap, along with the acrosome, is involved in the process of secreting
this enzyme.
It appears that after leaving the testis the only changes in morphology of sperm
are confined to the cytoplasmic cap and the drop, the former undergoing partial
regression, while the latter changes its position. According to Milovanov [1934],
the spermatozoa of farm animals rotate round their longitudinal axis owing to the
asymmetrical structure of the head. Our observations on sperm development in
the ram, goat and Barbary sheep suggest that the sperm head in these species
does not show any asymmetrical structure during its development. The sperm
head in these species is flattened from side to side, and roughly biconcave in the
'on edge ' position. In the ' on flat ' view, the shape of the head is characteristic for
each species. The goat sperm and sperm of the Barbary sheep are more nearly
alike in appearance.
In the three species, the sperm are differentiated for motility very early in their
development, but movement of the sperm is suppressed by unfavourable environ-
mental conditions of which viscosity of the medium and high sperm concentration
are quite important [Rao and Hart, 1948b]. Although capable of slight movement,
active motility cannot be induced in sperm from the deeper regions of the male
reproductive tract, even when suitable conditions are provided. This raises the
question of the physiological maturity of the sperm. It is also noticeable that as
the cytoplasmic drop goes down the connecting piece, the sperm exhibit a slightly
more active movement. Finally, maximum motility is initiated in vivo in the
tail of the epididymis in the ram, the goat and the Barbary sheep. The factors
involved in the initiation of motility are probably the physiological maturity of the
sperm combined with the lowered viscosity and lower sperm concentration. It
appears doubtful, however, that the secretions of the tail of the epididymis have
any specific stimulatory effect on sperm movement.
Our observations on the induction of sperm motility are in direct conflict with
the accepted theories, in this respect. Epididymal fluid is considered to be the most
favourable medium for the maintenance of sperm viability. According to Milovanov
[1934] the low content of the epididymal fluid in chlorine ions and electrolytes