342
ELVEZIO OHIRARDELLI
remain intact. Incidentally, if the eggs entered the seminal receptacle,
it is difficult to understand how they could come out without causing
all the spermatozoa contained in the receptacles t o come out at the
same time. Once the egg has come into contact with the vagina, the
axis of its movement takes a sharp turn towards the outside in a
direction perpendicular to that of the longitudinal axis of the ovary. I n
this way quite frequently the eggs assume the shape of an L (Fig. 33).
When passing through the genital papilla, the egg is coated with a
resistant membrane, provided with an elastic peduncle by which it is
fixed to the substratum. The following eggs show an analogous
behaviour and follow exactly the same paths. Only the last egg moves
somewhat slower than the others, perhaps because it is not pushed by
the vis a tergo of other eggs, and for a small fraction of time it may stop
in the terminal part of the temporary oviduct.
It is, moreover, not possible to say whether the movemcnts of the
wall of the ovary are due t o contractions of the ovary itself, or instead
more simply due to thc active movement of the eggs. These progress
with amoeboid-like movements, but are very quick, as if they were
slipping through a well lubricated duct or were sucked towards the
outside. Their movement recalls in its peculiarities, though obviously
not for the same reasons, that of planarians. Nothing is as yet known
about the causcs of the movement, but everything leads one t o think
that the eggs, in this phase of their existence, are provided with a
certain mobility of their own. The whole process, which is so long and
complicated, does not last more than 20 or 30 sec and often even less.
Histological sections have confirmed that the eggs reach the opening
through a kind of canal between the two layers of cells that form the
walls of the vagina itself: this is formed by an outer flat epithelium and
a cylindrical epithelium lying towards the lumen of the vagina. The
two cellular layers are detached and the eggs come out, but without
entering the vagina. I n this case, therefore, a temporary oviduct seems
to form, similar to the one described in Sagitta, with this difference,
however, that the penetration of the eggs occurs here at one point
only of the vaginal wall, and this is because the eggs all follow the same
path as the first one. The seminal pouch is not concerned in this case,
though it runs ventrally along the whole ovary. Another difference is
the noticeably shorter length of the temporary oviduct in Spadella,
limited to a small length only of the vagina which is 80-100 p long. I n
Sagitta, on the contrary, the oviduct may be as long as the ovary, in
some cases even some millimetres.
The disorganization of the cellular elements at the moment of
laying the eggs is, however, greater in Spadella than in Sagitta; to
ELVEZIO OHIRARDELLI
remain intact. Incidentally, if the eggs entered the seminal receptacle,
it is difficult to understand how they could come out without causing
all the spermatozoa contained in the receptacles t o come out at the
same time. Once the egg has come into contact with the vagina, the
axis of its movement takes a sharp turn towards the outside in a
direction perpendicular to that of the longitudinal axis of the ovary. I n
this way quite frequently the eggs assume the shape of an L (Fig. 33).
When passing through the genital papilla, the egg is coated with a
resistant membrane, provided with an elastic peduncle by which it is
fixed to the substratum. The following eggs show an analogous
behaviour and follow exactly the same paths. Only the last egg moves
somewhat slower than the others, perhaps because it is not pushed by
the vis a tergo of other eggs, and for a small fraction of time it may stop
in the terminal part of the temporary oviduct.
It is, moreover, not possible to say whether the movemcnts of the
wall of the ovary are due t o contractions of the ovary itself, or instead
more simply due to thc active movement of the eggs. These progress
with amoeboid-like movements, but are very quick, as if they were
slipping through a well lubricated duct or were sucked towards the
outside. Their movement recalls in its peculiarities, though obviously
not for the same reasons, that of planarians. Nothing is as yet known
about the causcs of the movement, but everything leads one t o think
that the eggs, in this phase of their existence, are provided with a
certain mobility of their own. The whole process, which is so long and
complicated, does not last more than 20 or 30 sec and often even less.
Histological sections have confirmed that the eggs reach the opening
through a kind of canal between the two layers of cells that form the
walls of the vagina itself: this is formed by an outer flat epithelium and
a cylindrical epithelium lying towards the lumen of the vagina. The
two cellular layers are detached and the eggs come out, but without
entering the vagina. I n this case, therefore, a temporary oviduct seems
to form, similar to the one described in Sagitta, with this difference,
however, that the penetration of the eggs occurs here at one point
only of the vaginal wall, and this is because the eggs all follow the same
path as the first one. The seminal pouch is not concerned in this case,
though it runs ventrally along the whole ovary. Another difference is
the noticeably shorter length of the temporary oviduct in Spadella,
limited to a small length only of the vagina which is 80-100 p long. I n
Sagitta, on the contrary, the oviduct may be as long as the ovary, in
some cases even some millimetres.
The disorganization of the cellular elements at the moment of
laying the eggs is, however, greater in Spadella than in Sagitta; to