JEAN C. DAN
Tokyo MetropolitanU@:ivcrsity and Misaki @1'Iarinc Biological Station
tween four and eight centimeters
of the deeperbays
January. Theyoungadultscarryfullydeveloped eggsandspermfromthetime
of their first appearance,and during the succeeding
constantly,gradually increasing in size and shifting
the bays towardthe open sea. At the middle of March most of the animals
are at the upperlimit of the size rangeamid contain
sperm. There is a brief period during which the gametes are obviously
mal condition, after which the medusae completely
the Station. Nothinghas as yet been learned
species during the remaining nine months of the year.
The embryologyof S. saltatrixhas not been investigated
so far to rear larvae past the gastrulastage or to collect intermediate
method of inducingspawning was developed
Kume (1948).Since these animalsspawn
the dark in the laboratorycauses a copious
mately an hour,regardlessof the day-night
a previousexposure of ten to fifteen minutes
improvesthe reactivity to the stimulusof darkness.
Examinationof eggs taken from the ovaries during
noon reveals only immatureeggs, whereas spawned eggs are always fully mature.
is thus apparentthat the light-darkness change is the stimulus
the maturation divisions, and eggs removed
been so stimulatedgo through the maturation
All attemptsto fertilize such eggs by adding
however,so farfailed,as have methods
sperm suspensions,or adding sperm suspension
cut from animals just before spawning time.
fertilizable for only a very shorttime after
though the specific reason for this has not yet been determined.
Inorder to obtain eggsin theearliest
followingprocedure wasadopted: several
were placed in sea waterin separate containers
males invariably spawnfirst,it was possible
out unduehandling of the animals.)Females
placed either in a containerwith a shedding
shedsperm,and watched for thebeginning
also lose theirfertilizingcapacity after a very
saltatrix,a bell-shaped memberof the
in the inner waters
nearthe Marine beginningof
the animals breed
from the heads of
large quantitiesof eggs and
not in opti
from the waters
because of the failure
to the direct rays of an ordinary
the morning and early after
of for the beginning
of females which have
on the microscope
shed sperm to them have,
to â€œ¿?dryâ€• eggs shed from ovaries
It is thus obvious
their expulsion from the ovaries,
from the ovaries
such as mixing
shed egg and
that the eggs are
male or in sea water containing
water, to sea con
sea water into which the eggs are to be shed.
container, a sample was removed
animal pole, where the polar bodies have just been extruded,
the pronucleuslies in contact with the egg surface.
may sometimesbe found still adhering
ally lost in the course of shedding
Thereare no envelopinglayers or membranes,
before or after fertilization.
care niust be exercisedto ensure the presence of freshly shed sperm in the
As soon as eggs were observed
to a slide and observed
with the phase contrast
eggs (Fig.1) are slightlyoval with
and at the base of which
One or both of the polar bodies
to the polar region, although
and the handling of the eggs prior to observation.
so far as can be determined,
a depression at the
these are usu
base of a slight
unfertilized egg of
depression the extrusionof the second body.
of the egg pronucleus.
found in the fact that excess
eggs, even in the case of eggs which have been rendered
with sea water before the addition
Immediately after the penetration
develops,around the sperm tail, a tubular
creases in both length and diameter
sperm tail, which maintainsslight but continuous
into the egg. The walls of this â€œ¿?fertilization tubeâ€•are entirely
sperm tail is perfectly visible moving
second spermatozoan was found with its head well within the tube.
course of degeneration, duringwhich it continues
parently, any increment in material.
tion of the structure, as thoughsea water were an unfavorable
istence.Breaksappear in the walls, and the lashing
animalpole of the egg,theirmovements
structurefrom its place of attachment,
tenuated, although fragmentsof its can sometimes
Completeengulfment of the tail usually
is occurring, the egg becomes spherical,
appears. The egg pronucleus slowly leaves its original
surface, moving a short distance toward the center of the egg and showing a marked
evidence for the existence
for the free-swimming
sperm are found only around
enters the egg in the immediate vicinity
Furtherof some sort of specific
the animal pole of mature
on the part of the egg pronucleus is
of sperm suspension.
of the sperm head into the egg cortex,
for about five minutes
2a) which gradually
(Fig. 2bâ€”e),while the
is steadily being drawn
the tube. In several
cases a freelywithin
the size shown in Figure
2e, the tube begins
in size without,
In fact, there seems to be a chemical dissolu
medium for its ex
of the shortening
if there are other spermatozoa
and it gradually
be found after 20â€”30minutes.
requiresabout 15 minutes.
and the indentation
becomes more and more at
at the animal pole dis
JEAN C. DAN
FERTILIZATIONIN SPIROCODONSALTATRIX 415
tion of the cleavage pattern,
eggs failed to reveal any trace of the sperm head after it entered
safe to conjecturethat the union
activity,between10 and 14 minutes
wouldaccount for the increase in nuclear
afterthe stageshown in Figure
to be followedshortly by the appearance
position previouslyoccupied by the fusion nucleus.
Althoughthe most careful observation of these remarkablytrans
the egg, it
of the sperm pronucleus has occurred,
after the beginning
2n, the outline
of the cleavage
of the nucleus disappears
For a descrip
is made to Dan and Dan, 1947.
Eggsof the tubularioanthomedusan,
partof March, are
of which the eggs
In the mature
of a slight depression
spawnedinto sea water containing
fertilizingsperm always enters in the immediate
the sperm entrance point a tubular
velop around the sperm
egg. Thiscontinues to increase
after which a process of degeneration
the tube has become balloon-shaped
tip of the sperm tail is finally drawn into the egg.
The egg pronucleus moves a short distance from the periphery
of the egg.A marked increase
ning of fertilizationprobably indicates
although no astral activity is detectable.
of the maturation
at the completion
eggs, the pronucleus
at the animal
lies in contact with the surface,
pole.These eggs are fertilizable
freshly shed spermatozoa.
of such eggs with the phase contrast
at the base
microscope shows that the
vicinity of the egg pronucleus.
structure begins to de
for about five minutes,
tail as soon as the head of the sperm
and is more or less rapidly disintegrating,
At the end of about fifteen minutes
toward the center
after the beginin size between 10 and 14 minutes
the union@of the sperm and egg pronuclei,
DAN, K., ANDJ. C. DAN, 1947. Behavior of the cell surface during cleavage.
cleavage of Medusan eggs. Biol. Bull., 93: 163â€”188.
KUME, M., 1948. Ovulation and related
Breeding, 9: 270â€”271.
UCHIDA, T., 1927. Studieson Japanese
Tokyo Imp. Univ. Ser. IV, 1: 145â€”242.
VIII. On the
phenomena in Spirocodon saltatrix. Collectingand
hydromedusae.I. Anthomedusae. Jour. Fac.Sci.,
from beginning of observation.)
pearance of â€œ¿?fertilization
sperm tail gradually being drawn into egg.
disappearance of polar depression.
Increase in size probably indicates fusion of egg and sperm pronuclei. Sperm tail completely
drawn into egg,remnant of fertilizationtube
(f) Beginning of degeneration
of sperm head.
tube.â€• inand of
to move inward.
lost.(n)Typically spherical conditionof