Reprinted from JOURNAL OF MORPHOLOGY
Vol. 148, No. , April 1976 cg The Wi star Institute Press 1976
The Structure of the Ovarian Ball and Oogenesis in
KRISTINE H. ATKINSON 1 AND J. E. BYRAM
Tallahassee, Florida 32306
of Biological Science, Florida State University,
cystacanths, the genital primordium of the female acanthocephalan is trans-
formed from a fragmented mass of cells into discrete ovarian balls. This is ac-
complished by envelopment of free germinal cells by somatic tissue which origi-
nates from the ligament sac primordium. Germinal cell nuclei then undergo
repeated mitoses until about 21 days of development, with concurrent formation
of oogonial syncytia which occupy the interior of the ovarian bals. Oocytes
derived from these oogonia, move to the periphery of the germinal syncytia for
differentiation, growth, fertiization, shell formation, and release from the ovar-
ian ball. After oogonial proliferation ceases, continued growth of the ovarian ball
apparently results from increase in size of already present cells.
Free-floating mature ovarian balls are found in the dorsal ligament sac; each
consists of germ cells in various developmental stages, enveloped and pervaded
by a multinucleate matrix syncytium of somatic origin, which functions as a
follcle. Spermatozoa pass through the matrix cell for the internal fertilization
of mature oocytes. Myelinated structures of an undetermined nature were found
to correspond to previously reported polar bodies. After 100 days post-infection
the somatic matrix syncytium begins to manifest the degenerative effects of
aging. The germinal tissue exhibits no subcellular signs of senescence by 154
days, but decreases in amount in older worms.
Seven to nine days after infection of the definitive host (rat) by
The Acanthocephala comprise a small
phylum of obligate parasites which are un-
segmented worms, with an armed probos-
cis, a syncytial cytoplasmic epidermis, and
no digestive tract. Their tendency to de-
velop syncytial body structures is notable
course of infection, the shelled acanthor
larva is passed from the female worm into
the vertebrate host's feces, and upon in-
gestion infects the invertebrate intermedi-
ate host. The larva passes through the final
acanthor and subsequent acanthella stages
of development in the intermediate host
then transforms into the cystacanth which
is infective for the definitive host. When
ingested, the larva attaches to the defini-
tive host's intestinal mucosa and grows into
an adult worm. The sexes are separate
and dimorphic with the male smaller in
most species. Mature female worms release
shelled acanthors, which begin the cycle
71). In the
J. MORPH., 148: 391-426.
Acanthocephalan embryology has been
documented in detail (Nicholas and Hynes
65), but the events preceding cleavage of
the zygote have not been fully character-
ized. The formation of reproductive units
in acanthocephalans has remained specu-
lative (Kaiser, 1898; Meyer
63), and the nature of the
ovarian ball has not been properly appre-
ciated (for example, Hyman
The present paper describes the origin
morphology, and developmental aspects of
the acanthocephalan ovarian ball, a unique
female reproductive tissue.
MATERIALS AND METHODS
flushed out of the hemocoel of adult
1 Present address: Department of Zoology, Univer-
sity of Western Ontario, London, Ontario N6A 5B7,
2 Present address: Department of Pathology, Peter
Bent Brigham Hospital, Boston, Massachusetts 02115.
KRISTINE H. ATKINSON AND J. E. BYRAM
buffered saline (KRT: Read et aI.
Cystacanths with an everted proboscis or
abnormal appearance (e. , melanization)
were discarded. Young male Holtzman rats
Periplaneta americana into
in KRT. In most cases, 100% infection
was achieved, and all worms could be re-
covered until the number of individuals in
aging populations began to diminish.
Rats were kiled by cervical dislocation.
The small intestine was quickly removed
and the worms gently freed from the mu-
cosa. In mature infections, the males were
easily distinguished from females by their
diminutive size and visibilty of the testes.
Young worms (12 days and less) were
sexed on the basis that the males are more
opaque posteriorly than females when ex-
amined against a buff-colored background.
Although this method was not entirely re-
liable, ovarian tissue was significantly dif-
ferent from testicular tissue upon micro-
scopic examination. Young female worms
were sectioned after their anterior and
posterior portions were discarded.
After 16 days of growth in the rat, ovar-
ian balls could be separated by squeezing
the pseudocoel contents of a decapitated
female worm into KRT and straining
through fine nylon mesh. Separation was
not practicable for younger ovarian balls
because they are smaller and more nearly
spherical than older ones, so that they
passed through the mesh. Optimum fixa-
tion was achieved in situ up to 19 days
even when separation was possible, since
young isolated ovarian balls required more
delicate treatment than older ones. The
young tissue exhibited strong adhesive
properties and could be partially disinte-
grated upon contact with pipettes, glass-
ware and nylon mesh.
Optimum fixation for transmission elec-
tron microscopy of all stages was ob-
tained by fixation with 6% glutaraldehyde
in 0.1 M phosphate buffer at pH 7. , with
5 mM CaCI . The tissue was fixed 3-
hours at room temperature, then given
three 20-minute washes with 0.1 M phos-
phate buffer containing 5% sucrose and
5 mM CaCI2. The tissue was postfixed
( 1 % OsO. in 0. 1 M phosphate buffer, with
with 1 % sucrose and 0.5 mM CaCI2) for
90 minutes, rinsed twice with tap water
and dehydrated through absolute ethanol.
with 25 cystacanths
The samples were given four 20-minute
changes of absolute ethanol, then brought
through propylene oxide and infiltrated
overnight with a 1: 1 mixture of propylene
oxide/epoxy (Epon or Epon-Araldite).
After two I-hour changes of Epon, the
tissue was usually flat-embedded, to facil-
tate the handling of isolated ovarian balls
which would not readily sink to the bottom
of a capsule, and to orient cross sections
of whole worms. Epon was polymerized at
C for three days.
Whole mounts were made following
fixation of ovarian balls for electron micro-
scopy (fig. 1). A drop of Epon containing
specimens was placed on a glass slide,
then a coverslip was applied and the prep-
aration was polymerized with the blocks.
Silver-gray sections for electron micros-
copy were cut with diamond or glass
knives on a Sorvall MT-2 or Reichert OmU3
ultramicrotome and mounted on clean
copper grids. The sections were stained
with uranyl acetate-lead citrate and exam-
ined with a Hitachi HU-llC, a Philps 100,
200 or 201, or an RCA EMU-3F electron
microscope. Thick epon sections (1 J.m)
were also cut on the ultramicrotome and
stained with methylene blue-azure II
(Richardson et aI.
usually were employed to determine the
three dimensional extent of observed struc-
tures, and to avoid misinterpretation of
planes of section. Dimensions reported
were averaged from at least ten typical
specimens viewed with light microscopy.
Since the width of the matrix syncytium
varied depending on the size and position
of underlying cells, the matrix cell periph-
eral radius was measured in areas overly-
ing mature oocytes. Dimensions of nuclei
and nucleoli are only approximate because
of their small size.
Tissue for light microscopy was fixed in
Carnoy s fixative for at least 24 hours. The
tissue was stained with eosin to facilitate
location, transferred through alcohol to
xylene and embedded in paraffn. Paraff
sections of 4 J.m were cut on an American
Optical Spencer microtome. Standard meth-
ods were employed for Feulgen and hema-
60). Serial sections
The ovarian tissue of M.
studied at stages from one week of devel-
THE OVARIAN BALL AND OOGENESIS IN
oprnent in the definitive host to over five
months after infection. A generalized out-
line of ovarian ball development and struc-
ture follows as an aid to understanding the
detailed descriptions of each time period.
Ovarian balls were formed by envelop-
ment of germinal cells by somatic tissue.
Envelopment commenced prior to 7.5 days
after infection of the rat, and was com-
pleted at 9-12 days. Several gonial cells
were surrounded by a syncytial matrix cell.
The gonial cells underwent a series of mi-
totic divisions from 12-21 days, fillng the
interior of the ovarian balls and forming
oogonial syncytia. Oocytes were derived
from the central oogonial syncytium (per-
vaded by the matrix cell) by fragmenting
or pinching off of individual germ cell nu-
clei surrounded by a little cytoplasm, after-
wards moving to the periphery of the
ovarian ball for further growth and differ-
entiation. Shell layers were probably elab-
orated after spermatozoan penetration, and
by 21 days acanthor release began in most
After assumption of its basic form by
12 days, the ovarian ball increased in size
to about 60 days, exhibiting signs of aging
by 106 days. The average size of ovarian
balls and the number of shelled acanthors
produced decreased with age beginning 60-
80 days after infection.
At 7.5 days, the ovarian ball was not yet
formed. The diameter of the worms was
3 mm, and the body fluid was gel-like
and viscous. The ovarian rudiment, 95
in diameter, lay in the lumen of the dorsal
ligament sac encircled by a unicellular bar-
rier that forms the inner aspect of the liga-
ment sac (fig. 2). The nucleoli of some
cells were enlarged (2.8 J.m, contrasted
with 2.3 J. in other cells) and dense, and
there was a slight difference in stain af-
finity among the cells seen with light mi-
croscopy. The rudiment was fragmented
and extensions of the cellular ligament sac
leading into the interior of the ovarian
rudiment began to enclose the germinal
cells (a movement established by observa-
tions of later stages, see below). Cells were
about 9.5 J.m in diameter, excluding ex-
tensions. Enveloped cells were sometimes
in a state of nuclear division.
Electron micrographs demonstrate points
of cellular interaction between the envel-
oping and enveloped cells (figs. 5, 6)
Plasma membranes were often indistinct
near points of contact. Enveloping cells
were long and tenuous (fig. 6) and were
seen to surround several comparatively
globular germ cells (identified in later
stages). Electron microscopy revealed fixed
among the cells a material which may cor-
respond to the viscosity of the body fluid.
Also present were extracellular structures
(fig. 5) similar in appearance to the my-
elin figures evident at 12 days. At the ul-
trastructural level there was no notice-
able dissimilarity ' to distinguish cellular
types (fig. 6). The cytoplasm of all cells
was similar, filled with polyribosomes and
generally resembling the undifferentiated
oocytes of later stages. Mitochondria were
relatively abundant, and sometimes con-
tained small electron-dense inclusions. In
transverse section, nuclei occupied major
portions of the cells (4.
cells). Nucleoli were condensed, fibrilar in
substructure and large, especially in en-
veloped cells. Long profiles of smooth en-
doplasmic reticulum were present, often
paralleling the plasma membrane or in
branched conformation. Golgi complexes
were sometimes found, but did not exhibit
the features later encountered during shell
production. Few other organelles or inclu-
sions were found. No granules or lipid drop-
lets could be detected.
J. in 9.5 J.
Mter nine days of development in the
definitive host, both sexes of M.
were 7-10 mm in length (dimensions of
individual worms were more nearly equal
than at 7.5 days), and the worms were
more slender and less opaque than previ-
ously. The body fluid of the worms was
In thick Epon sections, incomplete and
newly formed ovarian balls were seen in
the ligament sac (fig. 3). The ovarian balls
were clearly seen to be composed of two
cellular types: the enveloping type, which
had a uniformly dense (i.e., electron
opaque) cytoplasm with an enlarged nu-
cleus (8.5 J.m) and nucleolus (2.4 J.m);
and a second type, which averaged 9.4 J.m
in diameter and was characterized by more
granular ("lighter ) cytoplasm and rela-
tively smaller, less dense nuclei (5.6 J.
KRISTINE H. ATKINSON AND J. E. BYRAM
and nucleoli 1.9 J.). In sectioned ma-
terial, each ovarian ball consisted of at
least three of the latter cells, having granu-
lar cytoplasm, surrounded by a cell of the
dense type. The dense enveloping cell is
subsequently termed the
later development, matrix cells showed
evidence of being multinucleate, but at nine
days more than one matrix cell nucleus
was rarely found, even in serial sections.
In some specimens, the fragmented ap-
pearance of 7. day ovarian balls was stil
manifested, indicating that development
was probably not synchronous among all
worms at this early stage.
In sections through rudimentary ovarian
balls enclosed within the ligament sac, the
continuity of the matrix cell enveloping
the granular-type cells was readily appar-
ent. Serial sections of ovarian balls of all
ages did not give any indication that the
matrix cell consists of more than one cell
which has one to six nuclei with enlarged
dense nucleoli. Individual ovarian balls
vary in size, which may be a function of
the number of germ cells originally envel-
oped. At nine days, the ovarian balls were
irregular in shape, with protrusions where
the matrix cells invested the distal points
of the granular cells. In some advanced
specimens, surface elaborations resembling
microvill had formed on the outer surface
of the matrix cell.
The cellular ligament sac surrounding
the young ovarian balls was diminished
in thickness, and started to assume the
membrane-like appearance characteristic
of later periods. The ligament sac stil en-
closed the gonadal tissue, and varied in
thickness from 0.
8 J.m. Although inter-
cellular gaps were stil considerable, ovar-
ian ball formation was almost complete
and the interior cells were usually well
enveloped. These germ cells eventually
give rise to the oocytes, as is demonstrated
in later periods. At this point, they can be
likened to gonial primordia.
Electron microscopy disclosed no signi-
ficant cytoplasmic differentiation beyond
the 7. day stage. Polyribosomes were
abundant (more in germ cells than in the
matrix cell), and mitochondria were more
numerous. Profiles of smooth endoplasmic
reticulum were stil extremely long and no
rough endoplasmic reticulum was found.
The matrix cell cytoplasm was homogene-
ous from main body to periphery, with
mitochondria distributed evenly in the
outer aspect of the cell. One exception to
this uniformity was the existence of long
profiles of smooth endoplasmic reticulum
at the periphery and their absence in the
interior of the matrix cell; however, these
long membranes soon disappeared. Simi-
lar organelles were encountered in later
oocytes, usually in association with the
spindle apparatus. Microtubules appeared
in the same vicinity with a diameter half
that of the profiles of the endoplasmic
At 12 days, the worms were 3 cm long,
rather translucent, and the testes within
the males were easily visible with the naked
eye. The ovarian balls were ellpsoidal and
more regular in outline than at nine days
(figs. 4, 7). More cells, often 10-
3 J.m in diameter, were found embedded
in the matrix cell. This increase in the
number of cells probably resulted from di-
vision of germ cells (see below) to form
oogonia and the first oocytes (it was noted
that some oocytes begin to differentiate by
14 days). Envelopment was now complete
with no gaps remaining around the pe-
riphery of the matrix cells, and all of the
ovarian balls appeared to be entire. The
matrix cell nucleus was 7.5 J. in diam-
eter, with a 3.3 J.m nucleolus. Oogonial nu-
clei and nucleoli averaged 4.7 J.m (very
indistinct) and 1.4-1.9 J.m respectively.
There were often two small dense particles
in the vicinity of oogonial nucleoli.
Considerable variation occurred at 12
days in the stages of different infections,
probably a reflection of the intense mor-
phogenetic activity. Individual worms with-
in the same infection might vary greatly,
but in a single worm all the ovarian balls
displayed the same general characteristics.
Although light microscopy did not re-
veal great differentiation occurring be-
tween 9 and 12 days, the ultrastructure of
the 12-day ovarian ball (fig. 8) was mani-
festly different from that of its predeces-
sors. The matrix cell cytoplasm was now
unequivocally distinguishable from that of
the enclosed granular cells. The latter shall
henceforth be termed gonial primordia
THE OVARIAN BALL AND OOGENESIS IN
(before proliferation) or oogonia, since
they eventually give rise to oocytes.
The matrix cell cytoplasm appeared
denser, more uniform and with fewer or-
ganelles. There was an occasional Golgi
complex, some mitochondria and many
microtubules. Some areas were abundant
in polyribosomes, often in apposition to a
gonial plasma membrane. These areas of
apposition also exhibited blebbing of gonial
and matrix cell membranes. The peripheral
region of the matrix cell contained few
cytoplasmic organelles other than small
amounts of smooth endoplasmic reticulum.
Small lumina occurred in the matrix cell
cytoplasm, sometimes at the cell periphery
but most often in the interior. The spaces
separating the gonial and matrix cells were
large (with occasional points of contact at
which the membranes became indistinct).
With optimal fixation, myelin figures were
commonly found wedged between matrix
and germinal cells in young (less than 21
days) specimens (figs. 8-10). The nu-
cleoli of matrix cell nuclei were greatly
enlarged (fig. 9).
The oogonial cytoplasm was studded
with polyribosomes (except in actively di-
viding cells, in which ribosomes were un-
aggregated), and was more electron-lucent
than that of the matrix cell. Fields of mito-
chondria were often localized in one area.
The nucleus took up most of the area with-
in the oogonium, as in earlier specimens.
Two nucleoli occurred as often in small
nuclei as in large ones, and there were
sometimes one to three small dense bodies
near the nucleolus. The gonial cellular out-
lines were stil quite irregular, often with
finger-like projections extending into the
interior of the ovarian ball and interdigitat-
ing with the matrix cell (fig. 10). In some
advanced individuals (fig. 12), vesicles
with shell-like material were abundant in
the vicinity of the Golgi complex, and the
first fully formed granules were nearby.
No lipid droplets were present. There was
some smooth and rough endoplasmic re-
ticulum, but this may be associated with
the extensive presence of spindle-associ-
ated endoplasmic reticulum. Annulate
lamellae were first apparent in these early
germ cells, as was a multivesicular body.
The multivesicular body was regularly
found near the distal end of the spindle
often near patches of mitochondria, dense
bodies and the Golgi complex. It was mem-
brane-limited, and contained many smal
vesicles of irregular form.
Microvill were elaborated on the matrix
cell su,face at irregular intervals (fig. 11),
and seemed to have tubular internal or-
ganization. There was no terminal web or
underlying clear ectoplasmic zone as are
usually characteristic of extensive fields of
66). These projections
were often at various angles to the surface
of the ovarian ball, and were in dense
patches in some areas and totally absent
from others. Thus, these microvill do not
constitute a brush border of the type en-
countered in oocytes of other animals.
With the onset of surface amplication
the peripheral portion of the matrix cell
exhibited caveolae which look like pits
lined with tiny granules, often continuous
with the surface (cf. fig. 13), and coated
vesicles were also present. Tufts of very
long microvill were visible even with the
light microscope; thick and thin sections
demonstrate that these were indeed micro-
vill and not spermatozoa, as had been re-
ported by Nicholas and Hynes, ('63).
At 12 days, the gonial nuclei entered a
stage of intense activity, and various stages
of nuclear division were seen with both
light (fig. 7) and electron microscopes.
The synaptinemal complexes characteristic
of meiotic prophase (zygonema and pachy-
nema) seemed apparent in some oocyte
nuclei at 12 days. The enlarged nucleoli
contained large fibrilar zones,
The ligament sac (fig. 11) had materials
associated with both the internal and ex-
ternal surfaces. The cytoplasm of the sac
was electron-lucent and very homogeneous
except for a few microtubules and alter-
nating patches of denser cytoplasm, the
latter punctate in appearance. These may
be microfilaments in cross section, a likely
component of a structural element such as
the ligament sac. The surface of the sac
was elaborated into multiple laminae at
divers points on either side (fig. 11). The
entire ligament sac cross section was pe-
riodically constricted, up to a third of the
average width (fig. 9).
From 14-18 days of growth in the de-
KRISTINE H. ATKINSON AND J. E. BYRAM
was found in a
finitive host , M.
small area of the upper midgut. A few
worms were found
and off-white, granular copulation caps
were sometimes encountered on females
from 15-21 days. It was found on day 16
that the bursas of males were often
everted and one male emitted a stream
of whit fluid. when touched with a probe.
The parasites measured from 3.
in the next two days they in-
creased in length by ' about 3 . cm. The
length of a 14-day ovarian ball is 75-
93 J., twice the 12-day size, and at 18
days the ovarian balls are about 180 J.m
long, doubling again.
From 14-'18 days , theoogonia showed
repeated nuclear divisions, so that the
ovarian balls were packed .with' small ger-
minal nuclei. ' The oocyte nuclei, on the
other hand, remained rather stable in size:
as the cells grew from 14.
nuclei remained at .
and the nucleoli about 2.0 J.m (or 2.8 J.m
on day 18). At 15 days, some oogonia were
stil peripheral, with the nuclei occupying
most of the volume (fig. 14); however, at
16 days they had moved inward, leaving
only oocytes at the periphery. Cross sec-
tions of an ovarian ball at 16 days revealed
about 20 cells, compared with six or less
at 12 days.
This rapid expansion of cell number is
reflected in greatly decreased intercellular
spaces and the very tenuous envelopment
of the oogonia and oocytes by the matrix
cell. At 15 days, some oogonial cells seemed
to retain faint cellular outlines with ' the
light microscope (fig. 14), but at 16 days
only nuclear membranes delimited oogonial
cytoplasm. All oocyte nucleiwete compar-
able in size, but advanced oocytes (with
shell granule formation as an indicator)
had a much larger cell volume. Few small
oocytes were present. Elongation of the
ovarian balls by 18 days permitted visuali-
zation of more matrix. cell cytoplasm be-
tween oocytes. The dense appearance of
shell granules with light microscopy could
be seen in afew oocytes in many ovarian
balls at 14 days. With Epon whole mounts
oogonial nuclei seemed less transparent
than peripheral oocyte nuclei.
Spherical homogeneous objects were
noted with the light microscope in the
on day 15,
6 p. in diameter
vicinity of ovarian balls at 18 and 19 days.
Similarity to 7. day testicular tiSsue war-
rants further study of these structures as
With light microscopy, the ligament sac
looked more granular at 14 days, while
electron microscopy showed an unusual
compartmentalization of the cytoplasm.
The blebbing and variation in width of this
sac deserve further scrutiny.
Electron microscopy revealed the pro-
gressive contrast between matrix and ger-
minal cytoplasms. There were a few dif-
ferences at 12 days, but at 14 days the
difference in electron density was marked
(fig. 13), this difference increasing until
it reached a plateau at 21 days. Oogonia
and especially oocytes became replete with
polyribosomes and inclusions such as shell
granules. Mitochondria and rough endo-
plasmic reticulum became progressively
rarer in the peripheral matrix cell cyto-
plasm, while small vesicles and pits be-
came " more frequent. Surface microvill
were more regtllarand abundant (fig. 16).
The whereabouts and character of the ma-
trix nuclei during this period were elusive
with both light and electron microscopy.
In our search for morphological evidence
of cytokinesis, small germinal cell proc-
esses or invaginations were not observed
to contain midbodies or cleavage furrows:
On the other hand, in almost every 16-day
specimen there were many' examples of
matrix cell processes appearing to cleave
the germ cell cytoplasm. These processes
often fingerlike (fig. 17), occasionally ex-
hibited lengthwise profiles of microfila-
ments, and evidently occupied the area of
separation of two gonial cells. Whether
these processes provide the divisive force
in the separation of oocyte nuclei from the
main body of the oogonial syncytium could
not be confirmed.
During this time period, female worms
grew at' a greater rate than the males.
Copulation caps were encountered through
21 days, and all worms were confined to a
small area of the upper small intestine.
From 18-19 days, the ovarian 'balls con-
tinued to increase in length but were es-
sentially the same width (70 J.). The
19-day ovarian balls (fig. 15) were flat-
THE OVARIAN BALL AND OOGENESIS IN
tened in comparison with the plumper 21-
day specimens. By 21 days, the ovarian
balls averaged 85 ,am X 195 J.. During
this time span, the viscosity of the female
body fluid greatly decreased. At 21 days
some ovarian balls began to release shelled
acanthors, although there was great varia-
tion in the size and maturity of individual
ovarian balls. The acanthors were only
57 J.m long and lacked the outer envelope.
Isolated ovarian bals were very low in
mass, for even when fixed they would re-
main suspended in solutions for hours
and had to be centrifuged for reagent
changes. The ligament sac was highly
folded, and stained poorly with methylene
The matrix cell from 12-21 days mea-
The size of the matrix cell nucleus re-
mained about 7.5 J.m with a 2.8 J.m nucle-
olus. Oocyte nuclei were regularly 6.6 J.
in diameter with a 1.9 J.m nucleolus. At
19 days, great diversity in oocyte diameter
existed, ranging from 9.4-37.6 ,am; this
may signal production of new oocytes, pos-
sibly stimulated by increased space avail-
able in the ovarian ball and the imminence
of acanthor release. This diversity in
oocyte size remained until very late stages.
When oocytes reached the 37.6 J.m size
they were always filled with shell granules;
as shell was elaborated, the cell decreased
greatly in size until release.
Excepting gross morphology and acan-
thor production, the ovarian balls from
19-, 20-, and 21-day worms were similar
in ultrastructure, The matrix cell became
increasingly tenuous, and the oocytes were
spherical, providing the least surface area
and maximum volume. Small projections
were sometimes encountered near the dis-
tal end of the spindle axis. The matrix
cell, oogonium and oocytes were filled with
organelles, and oocytes rich in shell gran-
ules were noticeably denser even with the
light microscope. The oogonial cytoplasm
also contained many mitochondria and
dense inclusions, a characteristic useful
in distinguishing it from matrix cell cyto-
In early stages of shell formation (fig.
18), mass production of granules was seen
in the oocyte, with no visible congregation
near the periacanthor gap, and the matrix
1.0 J. at the peripheral radius.
cell and oocyte plasma membranes were
stil closely apposed. In the intermediate
stages (figs. 19, 20), few shell granules
remained in the germinal cell and it was
invested by the primary shell layer, while
the matrix cell began to elaborate micro-
villi into the periacanthor gap. The oocytes
had larger mitochondrial groupings than
at younger stages, at least when they as-
sumed the active p ripheral position.
Oogonia usually had mitochondria mixed
equally with dense inclusions. The matrix
cell had many lumina, often filled with a
filamentous material similar to that pres-
ent in the periacanthor gap (fig. 19). Mi-
crovili on the surface of the ovarian ball
were slightly more numerous than at
days, and were similar in number to later
stages but not as long. The presence of
pits and coated vesicles at the surface of
ovarian balls underlined the role of the
matrix cell in nutrition.
After a month of development in the
definitive host, female worms measured
10-12 cm and were located in the upper
small intestine. Males lagged in growth
and were found farther down the intestine
than the females. The female body fluid
was thin, and it remained so for the re-
mainder of the time periods studied.
At 36 days, the ovarian balls appeared
essentially mature, only increasing in
length during the following month. They
now measured 130 X 250 J.m. Light mi-
croscopy showed the outline of the ovarian
bal to be regular except where disturbed
by the eruption of a shelled acanthor.
There was more matrix cell cytoplasm be-
tween the oocytes so that they were no
longer crowded together, and oogonia were
diffcult to delineate in the core regions.
The breadth of the peripheral region of the
matrix cell increased to 1.5-
remained so through 106 days. The matrix
cell nuclei and nucleoli had the same di-
mensions as earlier. Released shelled
acanthors often appeared denser than at
earlier periods with light microscopy, and
had an extra shell layer enveloping them
which increased their length to 94 J.m (57
J.m before elaboration of the extra layer).
Electron microscopy showed that the
matrix cell cytoplasm was more vacuolated
0 J.m and
KRISTINE H. ATKINSON AND J. E. BYRAM
than previously. There were large lumina
more lipid droplets, and mitochondria
were plentiful. The envelopes of the ma-
trix cell nuclei were stil quite regular.
Oocyte and oogonial cytoplasm was iden-
tical with that of earlier stages. Matrix
cell surfaces surrounding cells elaborating
shell material manifested long microvill
and a filamentous coating, extending to-
ward the acanthor, which had the same
appearance as the contents of vesicles in
the periacanthor cytoplasm. Periacanthor
matrix cell cytoplasm was tenuous and
filled with microfilaments.
By 38 days , M.
have appeared in the host intestine:
Crompton et aI.
72). These investigators
showed egg production to peak or plateau
usually 60 to 80 days post-infection. The
morphology of the 60-day ovarian ball
typifies this period. The ovarian balls
were at the maximal size of this study,
ranging from 140 X 250 J.m to 150 X 335
J.m. The regular ellpsoids of earlier stages
were more often elongate shapes deter-
mined by the size and position of the
oocytes developing inside (fig. 1).
With light microscopy, the matrix cell
around the periphery of the ovarian ball
appears narrow and homogeneous having
the appearance of a simple .membrane
which was the interpretation of classical
cytologists. The pleomorphic envelopes of
the matrix cell nuclei (fig. 21) undoubt-
edly gave rise to the impression that cen-
tral ovarian ball nuclei fragment to form
oocytes, for without knowledge of the on-
togeny of the structure, the fragmentation
hypothesis seems tenable in a 60-day ovar-
ian ball viewed with light microscopy. The
matrix cell nuclei were slightly larger at
60 days than previously -- 9.4 J.m at the
widest point, with a 2.5 J.m nucleolus-
and remained so thereafter.
Electron microscopy revealed the ovar-
ian balls were packed with mitochondria
shell granules, and other organelles. Oocyte
ultrastructure remained similar to that of
earlier periods (fig. 22), but the succession
of one oocyte after another actively pre-
paring for release was impressive. Lipid
was commonly encountered.
In areas of imminent acanthor release
the matrix cell contained smooth endoplas-
mic reticulum with wide cisternae, but
otherwise few organelles. This is another
instance, as with elaboration of microvill
where periacanthor surfaces of the-matrix
cell assume the characteristics of the
peripheral region of the matrix cell prior
to acanthor release. There was often a
material present in the periacanthor gap
whose appearance resembled the contents
of the matrix cell vesicles. The periacan-
thor space arose before shell elaboration
began. Microvill on the matrix cell sur-
face appeared when the adjacent acanthor
was almost ready for release. Released
fully shelled acanthors were slightly larger
( 11 0 J.) than previously, and remained
so through 106 days.
The peripheral region of the matrix
cell was filled with microfiaments and
smooth endoplasmic reticulum (fig. 23).
The exterior surface, having few smooth
areas, was almost entirely elaborated with
tubular microvilli. Large protuberances
("knobs " see fig. 25) were remnants of
acanthor release, wherein a formerly inte-
rior surface was rendered exterior by evo-
lution of the periacanthor space. Some-
times smooth endoplasmic reticulum filled
the knob, another mark of periacanthor
cytoplasm. Enlarged lumina might also
have been an aftermath of acanthor dis-
charge. Spermatozoa were abundant in the
surrounding female body fluid, and large
cavities occasionally led down from the
The matrix cell contained huge fields
of elongate mitochondria, and in contrast
with earlier specimens, there were more
lipid droplets and lysosomes. The lyso-
somes were small, containing membranes
which were not thick and discrete as were
the myelin figures. Golgi complexes and
lipid were present sometimes even near
the periphery, and smooth endoplasmic
reticulum filled the matrix cell in the vicin-
ity of developing oocytes. The matrix cell
was tortuous at the center of the ovarian
ball, and a section would transect various
juxtaposed projections delineated from one
another by their contiguous plasma mem-
branes. The envelopes of the matrix cell
nuclei were more irregular at 60 days (fig.
23), and elongate patches of dense mate-
THE OVARIAN BALL AND OOGENESIS IN
rial appeared intermittently along the nu-
At 106 days after infection, the number
of adults recovered diminished to about
half of the 25 cystacanths initially admin-
istered, and males were few. The ovarian
balls decreased slightly in size, averaging
130 X 270 J.m. Although matrix cell nu-
cleus, oocyte, and oogonial dimensions
were the same as previously, there were
fewer oogonial nuclei and oocytes fillng
the ovarian ball. The matrix cell nuclei
were irregular in form and somewhat in-
The ovarian ball at this point was not
the highly effcient machine that it had
been at 60 days. There were fewer oocytes
and fewer shelled acanthors ready for re-
lease. The matrix cell cytoplasm was less
uniform than previously; elongate mito-
chondria and dense inclusions were stil
numerous; the number of lysosomes had
increased; and a multivesicular body,
which had smaller, rounder vesicles than
the structures occurring in oocytes, was
noted. The matrix cell at the periphery
was dotted with pits (fig. 24). Microvill
were more filamentous than previously
and were not as profuse as at 60 days (fig.
25), and microfilaments abounded in the
peripheral matrix cell cytoplasm. Surface
coats were not evident. Whorls of mem-
branes frequently occurred in the matrix
cell cytoplasm, and although these may be
fixation artifacts, they were never encoun-
tered in younger material. Lipid, especially
in oocytes, was particularly susceptible to
extraction during fixation.
The surface of the matrix cell surround-
ing zygotes undergoing shell formation ex-
hibited protuberances extending toward
the zygote. In more advanced cases, the
microvili became quite long, and were
comparable in appearance to the surface
elaborations of the 60-day martix cell. The
developing acanthors were similar in ultra-
structure to those observed at earlier and
later time periods.
In a rat examined 154 days after infec-
tion, male specimens of M.
entirely absent, and only four females were
recovered from an original infection of 25
cystacanths. The worms were yellowish
less plump than at earlier periods, and
were about 20 cm long. The amount of
body fluid and of ovarian balls and shelled
acanthors floating in the pseudocoel was
greatly reduced, and the ratio of ovarian
balls to shelled acanthors much higher
than in younger mature specimens. The
ovarian balls were shrunken in size, some
appearng quite shrivelled with light mi-
croscopy. The in vivo ovarian tissue was
not as brilliantly white as in younger
The ovarian balls were elongate in shape
with granular irregularities on the surface
and were reduced to 75 X 140 J.m; shelled
acanthors had decreased to 80 J.m in size.
Oogonia with more than one or two nuclei
(of previous dimensions) were rare, and
thus mostly oocytes, measuring 10-22 J.
even in early shell formation, remained.
Oocyte nuclei retained previous dimen-
sions, while the peripheral aspect of the
matrix cell was less than 1 J.m thick.
At this stage, a specimen was sectioned
for light microscopy containing a round
homogeneous object about 55 ,um in diam-
eter, similar to the objects seen at 18 and
19 days in situ. The structure was located
close to an ovarian ball and had a comet-
like appearance, with fibrous material issu-
ing from the compact head. The small
dense granules on the thin threads were
so reminiscent of spermatozoan conforma-
tion (fig. 25) that it is possible that this
was a spermatophore.
Electron microscopy showed that sper-
matozoa were present and presumably en-
tered the ovarian ball at 154 days. Since
males were absent, this observation implies
that the female has a means of sperm
storage. No worms had passed out of the
rat for at least three days prior to obser-
Surface microvill of the matrix cell
were not as plentiful as earlier, and were
absent in some areas (fig. 26). Surface
pits were stil present, although in reduced
numbers. Microfiaments were extensive
in the peripheral aspect of the matrix cell.
Large lumina perforated the matrix cell at
this stage (figs. 26, 27), often occupying
up to a third of the volume of the ovarian
ball. The number of lysosomes was greater
than previously, and they were occasion-
ally immense. Mitochondria were not as
plentiful as in stages of peak production
of offspring. Rough and smooth endoplas-
mic reticulum was uncommon, few Golgi
complexes of diminutive size and no annu-
late lamellae were encountered in this time
period. Some lipid was present, exhibiting
low osmiophila. Myelin figures were rare
inconspicuous, and only within lysosomes.
Multivesicular bodies (cf., 106 days) oc-
curred regularly in the matrix cell cyto-
Since the number of developing oocytes
was greatly reduced, tracing cell bounda-
ries and undulations of the matrix cell
throughout the ovarian ball was relatively
simple. The matrix cell nuclei were easily
located and were of a width similar to ear-
lier stages, but the nuclear envelope was
thrown into extensive contortions (fig.
26), folding back upon itself or projecting
far into the matrix cell cytoplasm. Mito-
chondria were concentrated in the peri-
nuclear area. Because the ovarian ball
was riddled with lumina and the amount
of matrix cytoplasm was scanty, the matrix
cell nuclei often looked like islands sus-
pended in a web of cytoplasmic strands.
Differences in the cytoplasm of the ger-
minal and somatic cells was less distinctive
at this point, since the matrix cell cyto-
plasm appeared more granular with less
electron-opaque ground substance. Oogon-
ial cytoplasm had fewer organelles and
dense inclusions compared to previous
stages, and all of the oocytes studied ap-
peared to be in interphase. Oocytes often
contained small lumina. Shelled acanthors
ready to be released were free in large
lumina surrounded by microvill of the
periacanthor matrix cell surface (fig. 27).
KRISTINE H. ATKINSON AND J. E. BYRAM
The classical concept of the acantho-
cephalan ovarian ball as a multinucleated
mass of syncytial cytoplasm surrounded
by developing oocytes was restricted by the
limitations of the light microscope (Meyer
51). What was viewed by
parasitologists as an enveloping membrane
is actually the peripheral portion of a sin-
gle syncytial cell, having an average of
three to five nuclei in a subperipheral to
central position. Entirely enclosed and
pervaded by this matrix cell is an oogonial
syncytium (syncytia?) and subsequent de-
velopmental stages up to and including
the shelled acanthor (fig. 28).
The fusion of somatic cytoplasm and
nuclei, originating from the ligament sac
primordium during ovarian ball morpho-
genesis, appears to determine the number
of matrix cell nuclei. The establishment
of a particular number of matrix cell nu-
clei early in development reflects the eutely
or cell constancy characteristic of acantho-
cephalans. This is typical also of the other
somatic tissues of
predetermined numbers of nuclei and show
no subsequent increase by fragmentation
as is seen in some members of this phylum
32). Although acantha-
cephalans are thought to have poor regen-
erative powers (Nicholas
tissue at least is highly plastic, and perhaps
inducible. To ilustrate, immediately prior
to acanthor release, the morphology of the
periacanthor surface of the matrix cell
undergoes a transformation and assumes
features normally associated with the outer
surface of this cell. This supportive cell is
highly elastic, adopting a variety of forms
like a skin, covering the protruding early
shelled embryos. This elasticity seems to
be an adaptation that minimizes cytoplas-
mic loss during acanthor release, which is
a definite asset considering the large num-
ber of embryos released from each ovarian
ball. The matrix cell cytoplasm pervading
the oogonial syncytium was termed ground
substance by Meyer (' 28); he designated
large, dense bodies of associated chromatin
as abortive embryos whose components
were thought to nurture developing 00-
cytes. These bodies were probably the
than germinal origin
nurse and follcle cells below) which we
suggest remain at a constant number.
The germinal tissue also appears to fol-
Iowa pattern of eutely, in that oogonial
proliferation seems to be accomplished
early in development (probably around 16
olas and Hynes
entiation, and growth then complete the
processes required for the production of
71), the matrix
matrix cell nuclei
of somatic rather
see discussion of
days in M.
THE OVARIAN BALL AND OOGENESIS IN
oocytes. It is very likely that little DNA
tissue after the major proliferation from
12-16 days; thus the increase in the over-
all amount of DNA in the body contents
of growing fertilzed female worms after
this time (Crompton
tirely accounted for by increased numbers
and growth of shelled embryos. The "divi-
sional figures" reported heretofore (Robin-
73) in older ovarian
balls must be carefully interpreted to avoid
confusion of nucleokinesis with true nu-
clear replication. This idea of early ter-
minal proliferation is supported by the
finding that Feulgen staining of germinal
nuclei was densest at 16 days (Atkinson
unpublished observation). The Feulgen
staining and the decreasing viscosity of
the body fluid after 16 days suggest at least
a partial role of hydration in subsequent
germinal tissue growth. The lengths of
the ovarian balls double from 14-18 days
and Feulgen staining of germinal nuclei
decreases rapidly after the 16-day peak.
Balinsky ('70) noted that because of nu-
cleic acid dispersion, germinal vesicles
(advanced oocyte nuclei bloated with nu-
clear sap) are more diffcult to stain with
the Feulgen reaction. We might assume
that an inverse relationship is true at 16
drated nuclei stain more intensely (cf.
71). A similar role of hydration
in the initial growth of the cystacanth after
entering the vertebrate host and being ac-
tivated may be inferred from the data of
Horvath ('69), where increased water per-
meabilty was identified as one of the
synthesis occurs in
72) should be en-
days in M.
physiological parameters of M.
velopment and growth leading to matura-
tion in the definitive host.
An ovary is an organ composed of ger-
minal tissue and supportive tissue (com-
monly nurse cells or follcle cells). Should
the process of initiation of de-
the matrix cell of M.
analogous to nurse cells or follcle cells?
For example, in the nurse cells of insects
molluscs, and annelids (Hughes and
Berry, '70; Balinsky, '70; King, '60), the cy-
toplasm serves to nurture the maturing
oocyte. The amplified surface area, caveo-
lae, and coated vesicles (Roth and Porter
64) of the acanthocephalan matrix syncy-
tium are suggestive of a similar nurturing
role. There are many decisive differences
however, in the nature of nurse and foll-
cle cells. Nurse cells arise from mitotic di-
visions of oogonial cells, and are siblings
of the oocytes (King, '60), whereas follcle
cells are of somatic origin (Balinsky, '70).
Several nurse cells are expended in nur-
turing a single oocyte, their cytoplasm
being engulfed or used up (Balinksy, '70),
while a group of follcle cells continuously
aids in the production of many offspring.
Lastly, an ovary may completely lack nurse
cells, but when present nurse cells are al-
ways accompanied by the somatic follcle
cells. The matrix cell of
sesses those properties common to follcle
cells in that: (1) the matrix cell and 00-
cytes of the ovarian ball differ in origin
and cytology; (2) a single syncytial matrix
cell supports the production of a large
number of shelled acanthors; and (3) al-
though the matrix cell conveys nutrients
from the female s body fluid and may fur-
nish such products as ribosomes to the
oocytes, it is not consumed by the oocytes
and does not seem to suffer any il effects
from this activity besides that of normal
aging. Thus the ovarian ball should be
considered to be an independent miniature
ovary, with the matrix cell functioning as
a syncytial follcle cell.
The primordial germ cells identified at
5 days of development in
are morphologically similar to germinal
anlagen of other systems (Spiegelman and
undifferentiated cells has been described
(King and Robinson
and the filipodial nature of the cells at 7.
days emphasizes the morphogenetic activ-
ity which is occurring. Similarity in dif-
ferential adhesiveness of matrix cells and
germ cells and the low cohesiveness of
germ cells are probably the basis of envel-
opment in this instance, as is the case with
the position adopted by vertebrate primor-
dial germ cells in relation to somatic meso-
derm (Steinberg, '62). In gonad forma-
tion, the spherical primordial germ cells
are interspersed among mesodermal cells
with those furthest from the site of release
remaining undifferentiated longest (Balin-
70). Migration of
KRISTINE H. ATKINSON AND J. E. BYRAM
sky, '70). The absence of any surface
elaboration on the cells, which could in-
crease the surface area for nutrient uptake
points to the precedence of organogenesis
over growth at this early stage.
The cytoarchitecture of ovarian ball
germinal cells at all stages reflects their
developing, embryonic nature, and the mor-
phological observations of subcellular dif-
ferentiation indicate intense developmen-
tal activity. Annulate lamellae (Kessel
72), multivesicular bodies (Calaro
72; N rrevang, '68; Anderson
64; Anderson and Beams
Golgi complexes (Mahowald and Hennen
71; N rrevang, '68) are present in the
maturing oocyte. The Golgi complex helps
to organize the mass production of mem-
brane-limited shell granules, a substance
required in quantity in initial development
(cf. other types of oocytes which are pro-
ducing yolk or cortical granules--Ander-
64; Brinton and Oliver
oli are dense and compact (Fawcett
64) and heterochromatin (Ca-
laro et aI.
tered, excepting that seen in condensed
chromosomes and the small amount occur-
ring in interphase nuclei. Ribosomes are
siton from unaggregated individuals in
dividing cells to polyribosomes in actively
synthesizing cytoplasm (Monroy and Ty-
63) is striking. The abundance of
ribosomes in the matrix cell in the vicinity
of oocytes, and the blebbing of their neigh-
boring plasma membranes suggest the
matrix cell as a source of ribosomes which
are crucial to early embryonic develop-
ment. Maternal contribution of ribosomes
is often encountered in the animal king-
65; Hughes and Berry, '70),
and ribosome uptake would be faciltated
by the extensive interdigitation of gonial
and matrix cells. The enlarged nucleoli
of the matrix cell are in harmony with
this hypothesis (Attardi and Almaldi
By means of transplantation studies
Crompton ('74) found that male worms
were incapable of successfully inseminat-
ing females prior to between 15 and 16
days post-infection. Worms transplanted
after 16-19 days showed a progressively
higher frequency of successful insemina-
tion. Our findings of copulation caps
61) is rarely encoun-
58) and their tran-
to 21 days, of males with extended copula-
tory bursas on day 16, and observations of
acanthor release from ovarian balls are
direct evidence supporting Crompton s es-
timation of the timing of initial insemi-
The events and timing of meiosis and
fertilzation must be clarified, with due
care for differing tissue types, changes dur-
ing the sequence of development, and
substantiated proof of the identity of
structures. Marshall et aI. ('73) reported
Feulgen staining of haploid polar bodies
51: pp. 21, 23) from
in the ovarian tissues of M.
ever, these intensely staining bodies as
seen with the light microscope proved to
be dense, myelin structures bearing little
resemblance to nucleic acids when
studied them with the electron microscope.
Schmidt ('73) stated " the polar bodies ap-
pear to mark the anterior end of the future
acanthor." The myelin figures appear in
this position and there is definite polarity
in oocyte development, but "polar bodies,"
by definition discarded meiotic chromo-
some sets, have not been identified. Be-
cause of such similarities in ovarian and
testicular ontogeny as syncytiality, dense
inclusions and original absence (persisting
in ovarian balls) of centrioles in the ger-
minal tissues (Whitfield
that acanthocephalan testicular develop-
ment would parallel this unique pattern of
The acanthocephalan ovarian ball of-
fers many opportunities to developmental
biologists. In vitro organ culture of this
tissue would facilitate the study of ovarian
development and differentiation; oogenesis
and polar body formation; spermatozoan
entry into the ovarian ball; fertilzation;
nutrition of the ovarian ball; matrix cell-
oocyte interactions; synthesis, storage and
deposition of shell proteins; and ovarian
71), we expect
The authors would like to express their
gratitude to Professor Robert B. Short for
his careful criticism of the manuscript.
The senior author is indebted to the De-
partment of Zoology of the University of
Western Ontario for the use of its electron
microscopy unit in the final stages of this
THE OVARIAN BALL AND OOGENESIS IN
study, and to Dr. Burr Atkinson for his
assistance in manuscript preparation.
Anderson, E. 1964 Oocyte differentiation and
vitellogenesis in the roach
J. Cell BioI., 21: 131-155.
Anderson, E., and H. W. Beams 1960 Cytologi-
cal observations on the fine structure of the
guinea pig ovary with special reference to the
oogonium, primary oocyte and assocIated foI-
licle cells. J. UItrastruc. Res., 3: 432-446.
Attardi, G., and F. Amaldi 1970 Structure a
synthesis of ribosomal RNA. Ann. Rev. BIO-
chern., 39: 183-226.
Balinsky, B. I. 1970 Introduction to Embryol-
ogy. Second ed. W. B. Saunders, Philadelphia,
pp. 60, 68-70, 483-487.
BIackler, A. W. 1958 Contribution to the study
of germ-cells in Anura. J. Embryol. Exp. Morph.,
1970 The integrity of the reproductive
cell line in the amphibia. In: Current Topics
in DevelopmentaI Biology. Vol. 5. A. Moscona
and A. Monroy, eds., Academic Press, New
York, pp. 71-87.
Brinton, L. P., and J. H. Oliver 1971 Fine
structure of oogonial and oocyte development
dae). J. Parasit., 57: 720-747.
Calaro, P. G., R. P. Donahue and D. Szollosi
1972 Heterochromatin during oogenetic de-
velopment. J. Cell Sci.,
Colwin, A. L., and L. H. Colwin 1957 Mor-
phology of fertilization: Acrosome filament for-
mation and sperm entry. In: The Beginnings
of Embryonic Development. A. Tyler, R. C.
von Borsteil and C. B. Metz, eds. Publication
No. 48 of the American Association for the
Advancement of Science, pp. 135-168.
Crompton, D. W. T. 1970 An Ecological Ap-
proach to Acanthocephalan Physiology. Cam-
bridge Monographs in Experimental Biology.
Vol. 17. Cambridge University Press, London
125 pp.1972 The growth of
(Acanthocephala) in the intestine of male
rats. J. Exp. BioI., 56: 19-29.
1974 Experiments on insemination in
sitology, 68: 229-238.
Crompton, D. W. T., S. Arnold and D. Barnard
1972 The patent period and production of
in the small intestine of male rats. Int. J.
Parasit., 2: 319-326.
Ebert, J. 1965 Interacting Systems in Develop-
ment. Holt, Rinehart and Winston, New York
pp. 75-80, 117-122.
Fawcett, D. W. 1966 The Cell. Its Organelles
and Inclusions. W. B. Saunders, Philadelphia
Horvath, K. 1969 The Physiology of Activation
ala). Ph.D. Dissertation, Rice University,
Houston, 75 pp.
Hughes, M., and S. J. Berry 1970 The synthe-
sis and secretion of ribosomes by nurse cells
Stiles (Acari: Ixodi-
Hyman, L. H. 1951 The Invertebrates. Vol. 3.
Acanthocephala, Aschelminthes and Entoproc-
ta. McGraw-Hil, New York, 572 pp.
Kaiser, J. E. 1898 Die Acanthocephalen unde
ihre Entwickelung. Bibliotheca Zoologic a 2
Kessel, R. G. 1968 Annulate lamellae. J. UI-
trastruc. Res., 24 (suppl. 10): 1-82.
King, D. E., and E. S. Robinson 1967 Aspects
of the development of
Parasit., 53: 142-149.
King, R. C. 1960 Oogenesis in adult
IX. Studies on the cytochem-
istry and ultrastructure of developing oocytes.
Growth, 24: 265-323.
Lyon, M. F. 1961 Gene action in the X-chro-
mosome of the mouse
Nature, 190: 372-373.
Mahowald, A. P., and S. Hennen 1971 Ultra-
structure of the "germ plasm" in eggs and
Marshall, J., R. N. Call and W. L. Nicholas 1973
A microspectrophotometric study of the DNA
of the embryonic and larval nuclei of
(Acanthocephala). J. Parasit.
Meyer, A. 1928 Die Furchung nebst Eibildung,
Reifung und Befruchtung des
Zool. Jb. Anat., 50: 117-218.
active ribosomal aggregates (polysomes) upon
fertilzation and development of sea urchin
eggs. Arch. Biochem. Biophys.,
Nicholas, W. L. 1971 The evolutionary origins
of the Acanthocephala. J. Parasit. , 57 (4, sect.
II, part II): 84-87.
Nicholas, W. L., and H. B. N. Hynes 1963 Em-
bryology, post-embryonic development, and
phylogeny of the Acanthocephala. In: The
Lower Metazoa. E. Dougherty, Z. Brown, E.
Hanson and W. Hartman, eds., University of
California Press, Berkeley, pp. 385-402.
1965 The embryology of
(Acanthocephala). Proc. Zool. Soc.
(London), 141: 791-801.
Nj'rrevang, A. 1968 Electron microscopic mor-
phology of oogenesis. Int. Rev. Cytol., 23: 113-
Read, C. P., A. H. Rothman and J. E. Simmons,
Jr. 1963 Studies on membrane transport,
with special reference to parasite-host integra-
tion. Ann. N. Y. Acad. Sci., 113: 154-205.
Richardson, K., L. Jarett and E. Finke 1960
Embedding in epoxy resins for ultra-thin sec-
tioning in electron microscopy. Stain Tech.
Robinson, E. S. 1965 The chromosomes of
Parasit., 51: 430-432.
Roth, T. F., and K. R. Porter 1964 Yolk protein
uptake in the oocyte of the mosquito
L. J. Cell BioI. 20: 313-332.
Schmidt, G. D. 1973 Early embryology of the
Cleave, 1916. Trans. Amer. Microsc. Soc., 92:
Devel. BioI., 23:
Develop. BioI. , 24:
A., and A. Tyler 1963 Formation of
KRISTINE H. ATKINSON AND J. E. BYRAM
Spiegelman, M., and D. Bennett 1973 A light-
and electron-microscopic study of primordial
germ cells in the early mouse embryo. J. Em-
bryol. Exp. Morph., 30: 97-118.
Steinberg, M. S. 1962 Mechanism of tissue re-
construction by dissociated cells. II: Time
course of events. Science, 137: 762-763.
Van Cleave, H. J. 1932 Eutely or cell con-
stancy in its relation to body size. Quart. Rev.
BioI., 7: 59-67.
Whitfield, P. J. 1971 Spermiogenesis and sper-
matozoan ultrastructure in
(Acanthocephala). Parasitology, 62: 415-
Wolfe, S. L. 1972 BioIogy of the Cell. Wads-
worth, Belmont, California, p. 453.
, Ligament sac
mc, Matrix cell
mcn, Matrix cell nucleus
, Body wal
, Dense bodies
, Myelin figure
g, Golgi complex
gc, Gonial cell
ob, Ovarian ball
pag, Periacanthor gap
pgc, Primordial germ
sg, Shell granules
sp, Spindle apparatus
EXPLANATION OF FIGURES
Epon-embedded whole mount of a 60-day ovarian ball of
The tiny nuclei of the central oogonial syncytium contrast
with the large oocytes maturing at the periphery. X 900.
The ovarian rudiment after 7.5 days of development in the definitive
host. Filpodia characterize the morphogenetic movements of the cells
at this time. Epon thick section. X 2,800.
Ovarian ball formation after nine days of development (advanced
specimen). This micrograph shows the ovarian ball fully formed with
the matrix cell nuclei in a central position (arrow), while other sec-
tions show the presumptive matrix cell and germinal cells stil in the
process of coalescence. Gonial cells are increasing in size. Epon thick
section. X 2,800.
Ovarian balls in situ at 12 days. The staining intensity readily distin-
guishes germinal from matrix cytoplasm. Some gonial cells have smal
dense bodies near the nucleolus (arrow). Epon thick section. X 2,500.
EXPI,ANATION OF FIGURES
Envelopment of primordial germ cells by somatic tissue at 7.5 days.
Cell surfaces are very regular. Close junctions of the plasma mem-
branes probably are involved in morphogenetic movements. The ex-
tension of somatic cytoplasm at x is shown in adjacent micrographs
to he enveloping the germinal cell at left. X 10500.
Interaction of somatic tissue and germ cells at 7.5 days. The somatic
tissue (X) is cxtending a long tendril of cytoplasm to envelop a pri-
mordial germ cell; some sections show envelopment of several germ
cells in a row by one tendril. At areas of cell contact, the plasma
membranes become indistinct. The cytoplasm of the two cell types is
very similaT. X 10 500.
EXPLANATION OF FIGURES
Mitosis in 12~day ovarian balls. The densely staining matrix cell nuclei
(x) are probably what Meyer ('28) termed abortive embryos. Gonial
nuclei are rather homogeneous, and the appearance of the nucleus at
the arrow may indicate the early developmcnt of an oocyte. Paraffn
section of whole worm staincd with hematoxylin. X 2 900.
Cytoplasmic features of the 12-day oVaIian ball. Early chromosome
condensation is seen in the germinal cell as well as the microtubule
aggregation suggestive of spindle formation. Note the extracellular
myelin figure between the matrix cell and the germinal cell. X 16 000.
Ultrastructure of an ovarian ball-ligament sac interface at 12 days.
The cytoplasmic nature of the ligament sac is evident, as well as its
surface coating. Early development of matrix cell surface elaboration
is evidenced by microvili and pits (arrows). Note the presence of
shell granules in the germinal cell at this early point in time. X 10 000.
EXPLANATION OF FIGURE
Cytoarchitecture of the ovarian ball prior to oogonial proliferation
(12 days). This matrix cell shows little cytoplasmic diversity and only
minor interdigitation with the gonial cells. Take particular note of
the extracellular myelin figures adjacent to the germinal cells. These
structures are located in the same position as the polar bodies re-
ported by various authors. X 10 500.
EXPLANATION OF FIGURES
Ultrastructure of the ovarian ball-ligament sac interface at 12 days
of development. Arrows indicatc multilaminar elaborations of the liga~
Ilcnt sac surface. The tubular core structure of the matrix cell micro-
vili can be seen. X 32 500.
Incipient cytoplasmic differentiation of a germinal cell. Twelve days
post-infection. X 29 500.
EXPLANATION OF FIGURES
The matrix cell and a gonial cell at 14 days. The absence of shell
granules in a cell as large as this indicates that it is a gonial cell
rather than an oocyte. This idea is supported by the lack of subcellular
differentiation fiuch as dense bodies, a Golgi complex and extensive
rough endoplasmic reticulum. Caveolae indent the matrix cell sur-
face (arrow). X 32500.
The ovarian ball 15 days after infection of the rat. Numerous mito-
chondria and dense inclusions dot the cytoplasm of the oogonial syn-
cytium. Epon thick section. X 2,900.
Lengthening of the ovarian balls at 19 days. Note particularly the
increase in size and the number of oocytes. When isolated, ovarian
balls were flattened at tbis time. Epon thick section. X 2000.
EXPLANATION OF FIGURES
The matrix cell surface at 16 days, Microvilli are longer and more
abundant than earlier. The lumen is a section through a large cavity
leading into the interior of the ovarian ball. X 29,000.
Relationship of the interior matrix cell and gDnial tissue at 16 days.
The extension of the matrix cell cytoplasm projects between two
nuclei of the oogonial syncytium. Microfilaments are often found in
the projecting tip of the matrix cell; vesicles preceding these projec.
tions are commonly observed. It is during this period of development
that the gonial cells become syncytial. X 19500.
EXPLANATION OF :FIGURES
Early shell formation in a 21.day oocyte. This oocyte is at almost maxi~
mal size and at the height of shell granule production. The matrix cell
stil closely invests the oocyte. X 15 000.
Intermediate shell formation in an oocytc of a 21-day ovarian ball.
The matrix cell is now separated from the zygote by the periacanthor
gap, which is filled with fiamentous material. The pcriacanthor matrix
ccll surface has begun claboration of microvili. Many shell granules
have disappearcd from the oocytc cytoplasm. X 15 000.
Jntermediate shell formation in a 21-day ovarian ball. The periacanthor
gap forms as the matrix surface recedes, but microvill have not yet
begun to form. Shell granules are concentrated at the periphery of the
new acanthar. X 18,750.
EXPLANATION O:F FIGURES
The matrix cell nucleus at 60 days. The highly folded nuclear en.
vclope has patches of dense material along the edges. A possible inter-
pretation of the patches is that they are oblique sections of the nuclear
envelope, an idea favored by the erratic conformation of the envelope.
X 18 300.
Substructure of the oogonial syncytium at 70 days of development.
The annulate lamellae, the Goigi complex and the rough endoplasmic
reticulum characterize this tissue. Note extcnsions of the matrix cell
in section at me. These extensions may playa role in the separation
of individual oocytes from the oogonial syncytium. X 7,600.
Matrix cell nucleus in subperipheral position at 70 days. The incidence
of matrix cell nuclei other than in the interior of the ovarian ball is
unusual at this time period. X 23250.
Sperm entry into a lOG-day ovarian ball. Note the intimate relation-
ship betwecn the spermatozoan tails and the matrix cell microvilli.
The spermatozoan seen in longitudinal section suggests that the mi-
crovili cnvelop and fuse with the spermatozoan plasmalemma. This
is reminiscent of a fertilization "cone" which draws down the sper-
matozoan as the cell regains its shape, in the manner of a cone
formed by a bulgc of cytoplasm (Colwin and Colwin
of passage of the spcrmatozoan through the matrix cell and entry into
the oocyte remain unknown. X 10500.
57). The means
EXPLANATION OF FIGURE
face, 106 days after infection of the definitive host. The cloud of
extracellular fibrous material is always found associated with the
spermatozoa. The membrane-bound dense bodies and the reticulate
condensation of nuclear chromatin (arrows) are described by Whit~
field ('71). A knob of the peripheral matrix cell remnant of ar.anthor
release is seen at lower left. X 17,000.
adjacent to the matrix cell sur~
EXPl.ANATION OF FIGURES
The external surface of a 154-day ovarian ball. The ovarian ball is
highly vacuolated, and the matrix cell nucleus is contorted. The
lumen (e) is one of the large cavities which occasionally lead to the
interior of the ovarian ball, and in which spermatozoa are often con
grcgated. The germinal cytoplasm at this point in time remains nor-
mal in appearance. X 12 000.
Interior of the ovarian ball at 154 days. Vacuolization of the matrix
cell is extreme, and the periacanthor gap is much wider than previ-
ously. X 12 000.
THE OVARIAN BALL AND OOGENESIS IN Download full-text
Kristine H. Atkinson and J. E. Byram
EXPLANATION OF FIGURE
A schematic representation of the acanthocephalan ovarian ball. This
figure is a composite of the morphological features demonstrated by
light and electron microscopy in the course of this investigation. The
relationships between cells are simplified so that basic concepts may
be easily grasped.