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Electron microscopic observations on the yolk sac of the Indian fruit bat Rousettus leschenaulti (Desmarest) (Pteropidae).

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Electron Microscopic Observations on the Yolk Sac
of the Indian Fruit Bat, Rousettus leschenaulti
(Desmarest) (Pteropidae)
K. B. KARIM,' W. A. WIMSATT,' A. C. ENDERS AND A. GOPALAKRISHNA
'Department of Zoology, Institute o f Science, Nagpur 440001, India; 'Section o f
Botany, Genetics and Development, Division of Biological Sciences, Cornell
Uniuersity, Ithaca, New York 14853 and "Department o f Human Anatomy,
Uniuersity o f California, Dauis, California 95616
'
ABSTRACT
The yolk sac of the Indian fruit bat Rousettus leschenaulti is
unique since during the course of development it becomes converted into a
solid, richly vascular endocrine gland-like structure with both the endodermal
and mesothelial cells undergoing substantial hypertrophy. The yolk sac is progressively drawn from the abembryonic (antimesometrial side) to the embryonic pole (mesometrial side) of the chorionic sac where in late stages i t comes
to rest against the placental disc. The endodermal cells become grouped into
clusters of acinus-like structures surrounded by the columnar mesothelial cells;
the yolk-sac lumen is in most instances obliterated. Individual endodermal cells
are large in comparison to mesothelial cells. The endodermal cell population
varies between cells with abundant agranular ER and areas devoid of organelles to others with dense cytoplasm containing stacks of granular ER. All endodermal cells have numerous mitochondria and a few lipid droplets.
The mesothelial cells are columnar with either dome-shaped, pointed or flattened apices bearing numerous elongate microvilli; within these are parallelarranged microfilaments. While the apical cytoplasm shows the presence of absorptive tubules, coated vesicles and caveolae, the basal cytoplasm contains
a few small mitochondria. Some mesothelial cells contain lipid droplets in
their basal cytoplasm. On structural bases i t is postulated that the mesothelial
cells are absorptive in function while the endodermal cells are synthetic and
secretory.
In bats unlike many other mammals the
yolk sac persists throughout pregnancy as a
functional entity, but the pattern of its differentiation and presumably its functions differ
profoundly among the major groups. In all the
Megachiroptera (Robin, 1881; Selenka, 1892;
Wimsatt, '54; Gopalakrishna and Karim, '72)
and in Tadarida brasiliensis cynocephala
(Stephens, '62) among the Microchiroptera
the yolk-sac splanchnopleure becomes completely separated from the chorion, shifts its
location towards the placental disc and undergoes progressive collapse with a near total
obliteration of the yolk-sac lumen. This is accompanied by an extensive hypertrophy of the
endodermal and mesothelial cells. Thus during the third trimester of pregnancy the yolk
sac comes to lie adjacent to the foetal surface
ANAT. REC. (1979) 195: 493-510.
of the placenta and has the form of a solid
gland-like structure. As stated by Mossman
('37) this unique modification of the yolk sac
is "not even suggested in any other known
group of mammals."
Information concerning morphological and
histological changes in the yolk sac of a few
Megachiroptera has been .provided through
the works of M. A. Moghe ('51, '561, S. Moghe
('561, and Karim ('72) but to date i t has not
been examined at the ultrastructural level.
This report provides an ultrastructural characterization of this uniquely modified yolk sac
in the Indian megachiropteran Rousettus
leschenaulti (Desmarest).
Received Jan. 22, '79. Accepted May 16, '79
493
494
K. B. KARIM, W. A. WIMSATT, A. C. ENDERS, A. GOPALAKRISHNA
MATERIALS AND METHODS
Near term specimens of Rousettus Zeschenaulti were collected from an abandoned
manganese mine tunnel a t Kandri, Ramtek,
India on 18th and 20th March 1977 and 5th
and 28th March 1978 and from Chandrapur,
Central India on June 29th, 1977. They were
brought to the laboratory and were killed with
ether. The uteri were removed and portions of
the yolk-sac gland were fixed in 3% glutaraldehyde in 0.1 M phosphate buffer (pH 7.2) for 3
hours, rinsed in phosphate buffer overnight in
the refrigerator and post fixed in 1%osmium
tetroxide in 0.1 M phosphate buffer (pH 7.2)
for one and one half hours. The tissues were
dehydrated in graded concentrations of cold
ethyl alcohol, passed through propylene oxide
and embedded in either Araldite (Durcupan),
or Epon 812 and Araldite 506 mixture. Thin
sections were stained with uranyl acetate for
30 minutes and 4 minutes in lead citrate prior
to examination in a Philips 200 electron microscope. For orientation and light microscopic study, thick (1-2 pm) sections of plastic
embedded material were stained with azure B.
Eighteen bats were used for this study.
For examination of surface topography, portions of the yolk-sac gland were fixed as for
TEM, then placed in acetone and critical point
dried from liquid CO,. The tissues were subsequently sputter coated with gold and examined in a Cambridge Stereoscan or Philips 501
scanning electron microscope.
OBSERVATIONS
Summary of yolk sac development
The morphological and histological changes
in the yolk sac during gestation in Rousettus
leschenaulti have been described by Karim
('72). To orient the reader it is pertinent to
review briefly these changes, which are summarized in figures 1-5 inclusive.
At the earliest stage (bilaminar blastocyst)
the endodermal layer consisted of flat squamous cells (fig. 2), joined to one another by
thin cytoplasmic processes. By the late limbbud stage the formation and expansion of
the exocoelom had not only separated the
Fig. 1 Semidiagrammatic representation of the stages in the morphogenesis of the yolk sac into a unique gland-like
structure in Rousettus. A, Bilaminar blastocyst stage; B, Late limb-bud stage; C, Mid-pregnancy stage; D, Definitive organization as seen during the third trimester of pregnancy. en, endoderm; mes, mesothelium.
ULTRASTRUCTURE OF YOLK SAC, FRUIT BAT
yolk-sac splanchnopleure from the chorion
over the entire circumference of the yolk sac,
but the endodermal cells had hypertrophied
and become columnar (fig. 3). By mid-pregnancy the splanchnopleuric wall had become
markedly folded or pleated (secondary folds).
A small crypt-like extension of the yolk-sac
lumen was incorporated within each fold (fig.
4). Progressively as development proceeded,
these endodermal crypts became detached and
their endodermal cells became arranged into
isolated acinus-like aggregates with small
central cavities embedded within the mesenchymal stroma of the yolk-sac wall. During
the final quarter of pregnancy a central yolksac cavity had completely disappeared and
most of the isolated lumina within the endodermal acini had also been obliterated by continued hypertrophy of the endodermal cells
(fig. 4).In consequence the solid yolk sac had
now assumed a gland-like appearance. In the
final quarter also the originally fusiform
mesothelial cells facing the exocoelom likewise hypertrophied and assumed a columnar
form (fig. 5). They not only invested the yolksac as a whole but also formed invaginations
which penetrated deeply between the endoderma1 cell clusters. The yolk-sac wall a t this
final stage was still richly vascularized.
Endodermal cells
Scanning electron microscopy
The acinar clusters of endodermal cells
invested by mesothelium and connective tissue were exposed by breaking small blocks of
yolk sac after fixation but prior to processing
for SEM. The “acini” were distinct, spherical
structures surrounded by fibrous elements of
the connective tissue (fig. 6).The endodermal
cells had relatively smooth lateral surfaces,
with a distinct amplification a t the apical borders where a series of small microvilli marked
the transition to the apical end of the cell (fig.
7).The basal surface was more irregular. The
cells were markedly prismatic. Fetal capillaries often lay close to the endodermal acini.
Transmission electron microscopy
Preservation of the yolk sac in all of the
blocks was poor, limiting the observations
that could be made by high magnification
transmission electron microscopy. Nevertheless, many of the aspects of the cytological organization of the endodermal cells were discernable. The individual endodermal cells
495
were much larger than the associated mesothelial cells, and had a large nucleus with
relatively little heterochromatin which was
bounded by a fenestrated nuclear envelope
and contained a distinct nucleolus. Occasional
endodermal cells had two nucleoli. Central
remnants of the original yolk-sac lumen occurred in the midst of quite a few “acini,” and
i t contained a n electron dense homogeneous
coagulum. In “acini” lacking a central lumen,
the apical ends of the cells nevertheless
showed junctional complexes, and intercellular spaces studded by small microvilli were
common. The lateral margins of the endoderma1 cells had a few blunt microvilli but were
otherwise relatively smooth. The basal surface of the endodermal cells abutting the
mesodermal stromal tissue had regions of appreciable folding adjacent to the basal lamina
(fig. 8).
The internal structure of the endodermal
cells ranged between two extremes. The
lighter cell tended to have large amounts of
agranular endoplasmic reticulum (ER) and
areas of cytoplasm devoid of most organelles.
In a few instances it appeared that glycogen
had been extracted from these regions. At the
other extreme, the darker cells had much
more granular ER rather than agranular ER,
and the granular ER was arranged in groups
of parallel cisternae. In all endodermal cells
the mitochondria were large with cristae that
did not extend across the individual mitochondrion. Most endodermal cells had whorls of
agranular ER arranged in concentric layers,
often surrounding one or more mitochondria.
Mesothelial cells
Scanning electron microscopy
When the surface topography of the mesothelial cells was examined in a scanning microscope a t lower magnifications it appeared
to be irregularly lobulated (fig. 10). The exocoelom extended into the crypts separating
the lobules. The surface of individual lobules
was covered by numerous mesothelial cells of
varied shapes and sizes. Conspicuous intercellular clefts separated the individual cells
from one another. The surface of the cells had
a warty appearance a t low power but when observed at higher magnifications (fig. 11)
showed the presence of numerous elongate,
irregular shaped microvilli projecting from
the apices and lateral margins of the cells. The
microvilli from the individual cell surfaces
496
K. B. KARIM, W. A. WIMSATT, A C. ENDERS, A. GOPALAKRISHNA
and those from adjacent cells intermingled
with one another and formed a delicate meshwork in the region of the intercellular clefts.
distributed throughout t h e cytoplasm (fig.
15).
The exocoelomic spaces projecting into the
consolidated tissue often contained a n electron dense coagulum and remnants of degenerating or lysing mesothelial cells (fig. 14).
Transmission electron microscopy
In sections the mesothelial cells facing t h e
exocoelomic surface were tall columnar with
DISCUSSION
e i t h e r dome-shaped, pointed, or flattened
Organogenesis of t h e yolk sac in bats disapices t h a t protruded into t h e exocoelom
above t h e level of t h e apical junctional com- plays three main trends: (1) The abembryonic
plex (fig. 9 ) . While intercellular spaces sur- segment of t h e yolk sac remains permanently
rounded t h e apical ends of most mesothelial bilaminar or trilaminar as in Desmodus rotuncells, extensive areas of membrane contact oc- d u s murinus (Wimsatt, '541, Noctilio labialis
curred along the lateral margins of some of minor (Anderson and Wimsatt, '631, Artibeus
t h e cells (figs. 12, 15). Where present the in- jamaicensis parvipes (Wislocki and Fawcett,
tercellular spaces reduced the area of lateral '411, Megaderma lyra lyra (Gopalakrishna,
intercellular association between t h e junc- '50b; Gopalakrishna a n d Khaparde, '781,
tional complex and the base of t h e cells. The Thyroptera tricolor (Wimsatt and Enders, '79)
cells bore numerous elongate microvilli of var- and all t h e vespertilionid bats (Ramaswami,
iable lengths protruding into t h e exocoelom '33; Wimsatt, '45; Gopalakrishna, '50a; Phanand into the intercellular spaces (figs. 11-14, salkar, '72; Gopalakrishna and Sapkal, '74;
16).The microvilli contained numerous micro- Karim, '76; Ramakrishna and Madhavan,
filaments arranged in parallel within their in- '77). (2) The yolk-sac splanchnopleure beterior; basally these filaments blended into a comes completely separated from the chorion,
zone of similar filaments forming a n irregu- progressively undergoes collapse, and is withlarly thickened terminal web in t h e apical cy- drawn from its original position and finally
toplasm of t h e mesothelial cells. The micro- comes to lie adjacent to t h e chorio-allantoic
villi had in addition a prominent glycocalyx. placental disc. The yolk-sac lumen persists,
The basal segments of the mesothelial cells however, as intercommunicating narrow
were highly folded (fig. 14) and t h e basal lami- streak-like spaces. The endodermal cells, and
na followed t h e contours of these folds. The sometimes also t h e mesothelial cells of t h e
nuclei of t h e mesothelial cells were highly separated yolk-sac splanchnopleure undergo
lobulated a n d nuclear fenestrations were hypertrophy, thereby giving the collapsed
prominent. D a r k aggregations of hetero- yolk sac a somewhat consolidated gland-like
chromatin lay against t h e nuclear membrane. appearance. This condition has been reportIn occasional sections a nucleolus was seen ed in Rhinopoma kinneari (Srivastava, '52;
within the nucleus. At some places, due to t h e Gopalakrishna, '581, Taphozous longimanus
crowding of the cells, the nuclei appeared to (Gopalakrishna, '581, Hipposideros bicolor
lie a t different levels within t h e epithelium. pallidus (Gopalakrishna, '58; Gopalakrishna
At many places the mesothelium was infolded and Moghe, '601, Hipposideros speoris (Jeebetween t h e endodermal acini, displacing t h e vaji, '731, Hipposideros fulvus fulvus (GOstromal connective tissue and t h e vitelline palakrishna and Karim, '75) and Rhinocapillaries. The cells assumed varied shapes, Zophus rouxi (Bhiwgade, '77). (3) The yolkand because of t h e limited space there was in- sac splanchnopleure becomes completely
termingling of t h e microvilli from adjacent separated from t h e chorion and shifts its locacells.
tion towards t h e placenta a s in 2 above, and
The apical cytoplasm of t h e mesothelial there is a complete collapse of the yolk sac.
cells contained absorptive tubules, coated ves- The yolk-sac lumen is in most instances comicles and caveolae (fig. 16). The basal cyto- pletely obliterated, the hypertrophied endoplasm was characterized by the presence of a dermal cells a r e rolled up into isolated acinusfew small mitochondria with lamellar cristae. like complexes, and the investing mesothelial
Occasional mesothelial cells also contained cells also hypertrophy in later stages. Thus,
lipid droplets in their basal regions. A small during t h e last quarter of pregnancy the yolk
Golgi complex was usually located lateral to sac acquires t h e form of a solid, vascular,
t h e nucleus. Numerous free ribosomes, micro- gland-like structure lying at t h e foetal face of
filaments and microtubules were eenerallv t h e placental disc. This apparently occurs in
-
ULTRASTRUCTURE OF YOLK SAC, FRUIT BAT
all the Megachiroptera (Robin, 1881; Selenka,
1892; Gohre, 1892; Sprenkel, ‘32; M. A.
Moghe, ’51, ’56; Wimsatt, ‘54; Gopalakrishna
and Karim, ’72; Karim, ’721, and among
Microchiroptera i n T a d a r i d a brasiliensis
cynocephala (Stephens, ’62).
Ultrastructural studies of the chiropteran
yolk sac have been limited to the microchiroptera species Tadarida brasiliensis cynocephala (Stephens and Easterbrook, ’68, ’69, ’71;
Stephens and Cabral, ’71) and Myotis lucifugus lucifugus (Enders et al., ’76).Stephens and
Easterbrook (’68, ’69, ’71) have shown that a
“membranous organelle” in the endodermal
cells of the yolk sac of Tadarida brasiliensis
cynocephala develops directly from the rough
endoplasmic reticulum and have suggested
that i t may be involved in glycogen and lipid
metabolism. Glycogen and lipid accumulate in
the endodermal cells of the yolk sac until late
stages of pregnancy but are depleted just prior
to parturition (Stephens and Easterbrook,
’69).
Stephens and Cabral (‘71) showed that the
mesothelial cells of the yolk sac develop an
“absorptive apparatus” and contain numerous
crystalloid-containing vacuoles which disappear near term. They postulated that the
mesothelium is involved in the absorption and
storage of proteinacous material from the
exocoelom for use by the embryo.
Enders et al. (’76) have shown that the en.
dodermal cells of the yolk sac of Myotis
lucifugus lucifugus develop an extensive system of agranular endoplasmic reticulum, numerous lipid droplets and unusual “giant” mitochondria. The mesothelial cells develop an
extensive “absorptive apparatus” in their apical regions and have numerous crystalloidcontaining granules in the basal cytoplasm.
These cells contain large deposits of glycogen
during mid-gestation, but few mitochondria
and little agranular endoplasmic reticulum a t
this time. The uptake of marker protein
(horseradish peroxidase) and possibly other
substances by these cells from the exocoelomic
fluid indicated that absorption is a major
function of the hypertrophied mesothelial
cells. They concluded further that a major
function of the hypertrophied endodermal
cells may be synthesis and secretion of substances into the foetal circulation.
As shown here the yolk sac of Rousettus
leschenaulti becomes converted into a solid,
vascular gland-like structure, with both the
endodermal and mesothelial cells undergoing
497
hypertrophy. The endodermal cells become
grouped into isolated acinus-like masses,
while the mesothelial cells retain their epithelial continuity. Thus the yolk sac of Rousettus,
typical in its definitive form of the Megachiroptera, most nearly resembles t h a t of
Tadarida brasiliensis cynocephala among the
Microchiroptera (Stephens, ’62).The mesothelial cells in Rousettus, as in Tadarida and
Myotis, develop an “aborptive apparatus” in
the apical cytoplasm and are similarly provided with elongate microvilli. However, the
mesothelial cells of Rousettus lack the crystalloid-containing vacuoles in the basgl cytoplasm described in Tadarida and Myotis.
The endodermal cells of Rousettus resemble
those of Myotis in bearing microvilli on any
free apical regions of the cells, presence of
smooth endoplasmic reticulum, stacks of
granular endoplasmic reticulum and large mitochondria. They differ, however, in t h e
possession of microvilli in lateral and basal regions of the cells and in the variation in cell
morphology to “light” and “dark” cell types.
The unusual transformations of the yolk sac
described here in a megachiropteran presumably signalize a physiological role(s) for the
organ during pregnancy which is probably different in some respects from the same organ in
other bats and it deserves further histophysiologic and biochemical analysis.
ACKNOWLEDGMENTS
Dr. (Miss) K. B. Karim wishes to thank the
Ministry of Education and Social Welfare,
Government of India for an award of a
National Scholarship for Post Doctoral Research in the United States.
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(Temminck). Proc. Indian Acad. Sci., 86: 61-72.
Enders, A. C., W. A. Wimsatt and B. F. King 1976 Cytological development of the yolk sac endoderm and protein-ahsorptive mesothelium in the little brown hat, Myotis
lucifugus lucifugus. Am. J. Anat., 146: 1-30.
Gohre, R . 1892 Dottersack und Plazenta des Kalong
(Pteropus edulisi. In: Selenka’s Studien uber Entw. d.
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Microchiroptera. Part V. Placentation in the vespertilionid hat, Scotophilus Lvroughtoni (Thomas). Proc.
Indian Acad. Sci., 31: 235-251.
1950h Studies on the embryology of Microchiroptera. Part VI. Structure of the placenta in the Indian
498
K. B. KARIM, W. A. WIMSATT, A. C. ENDERS, A. GOPALAKRISHNA
vampire bat, Lyroderma lyra lyra (Geoffroy) (Megadermatidae). Proc. Nat. Inst. Sci. India., 16: 93-98.
1958 Foetal membranes in some Indian Microchiroptera. J. Morph., 102: 157-197.
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gland of the lndian fruit-bat, Rousettus leschenaulti
(Desmarest).Curr. Sci., 41: 539-541.
1975 Development of the foetal membranes in
the Indian leaf-nosed hat, Hipposideros fuluus fuluus
(Gray). 11. Morphogenesis of the foetal membranes and
placentation. Rev. Roum. Biol., 20 (4): 257-267.
Gopalakrishna, A., and M. S. Khaparde 1978 Development
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false vampire bat, Megaderma lyra lyra (Geoffroy). Proc.
Indian Acad. Sci., in press.
Gopalakrishna, A,, and M. A. Moghe 1960 Development of
the foetal membranes in the Indian leaf-nosed bat, Hipposideros bicolor pallidus. Z. Anat. Entwl., 122: 137-149.
Gopalakrishna, A., and V. M. Sapkal 1974 Foetal membranes in the Indian pipistrellid, Pipistrellus dorrneri
(Dobson) J. Zool. SOC.India., 26: 1-9.
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Thesis, Institute of Science, Nagpur, Nagpur University,
Nagpur. India.
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Indian fruit bat, Rousettus leschenaulti (Desmarest). J.
Zool. SOC.(India), 24 (2): 127-147.
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S. Thesis, Institute of Science, Nagpur, Nagpur University, Nagpur, India.
Moghe, M. A. 1951 Development and placentation in the
Indian fruit bat, Pteropus giganteus giganteus (Brunnich). Proc. Zool. SOC.(London), 121: 703-721.
1956 On the development and placentation of
the megachiropteran bat, Cynopterus sphinx gangetrcus.
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gland in Chiroptera. Proc. Nat. Inst. Sci. India: B. Biol.
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the foetal membranes and accessory uterine structures.
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127-246.
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chrysothrix. Ph.D. Thesis, Institute of Science, Nagpur,
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edulisi. In: Studien uber Entwl. der Tiere, Heft 6.
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-in den Embryonen der Fledermause und ihre Ursiche. Z.
mi&.-anat. Forsch., 28: 185-268.
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bat, Rhinopoma kinneari. Proc. Zool. SOC.(Bengal), 5:
105-131.
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Stephens, R. J., and L. J. Cabral 1971 Cytological differentiation of the mesothelial cells of the yolk sac of the bat,
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292-312.
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1969 A new cytoplasmic organelle, related to
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Anat., 124: 47-55.
1971 Ultrastructural differentiation of the endodermal cells of the yolk sac of the bat, Tadarida brasiliensis cynocephala. Anat. Rec., 169: 207-242.
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1-51.
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PLATES
PLATE 1
EXPLANATION OF FIGURES
2 Free uterine blastocyst at the bilaminar stage of development. Note the cubical cells
of the trophoblast (tr) and the flat squamous endodermal cells (en) which are joined
to one another by thin cytoplasmic processes. X 250.
3 Part of t h e separated splanchnopleure of the yolk sac a t t h e late limb-bud stage.
Note t h a t t h e endodermal cells (en) have hypertrophied and become columnar. The
mesothelial cells (arrow) are still fusiform. x 560.
4
Part of the collapsed yolk-sac splanchnopleure a t mid-pregnancy. Note the marked
folding of the wall (secondary folds) and the inclusion of crypt-like extensions of the
yolk-sac lumen within each fold (arrow). x 80.
5 Thick section of part of the yolk sac during the final quarter of pregnancy to show
the acinar arrangement of the endodermal cells, “light” and “dark’ cells within t h e
endodermal acini, small remnants of the original yolk-sac cavity within some of the
endodermal acini (small arrows) and the hypertrophied mesothelial cells (long
arrows). Azure B. x 1.200.
500
ULTRASTRUCTURE O F YOLK SAC, FRUIT BAT
K B Karim, W A Wimsatt, A C Enders, A Gopalakrishna
PLATE 1
501
PLATE 2
EXPLANATION O F FIGURES
6
SEM view showing fold of yolk sac broken to reveal the isolated clusters of endoderma1 cells, extending from the lower left to right center. Note t h e large size of the
endodermal cells (short arrows) as opposed to the mesothelial cells (long arrow).
x 850.
7 A higher magnification of t h e “acinus” seen in t h e lower left of figure 6. Note the
prismatic nature of the cells, the microvilli a t the apical ends of the cells (arrow),
the smooth lateral walls and the irregularity of the basal surface. Connective tissue,
CT. X 1,700.
502
ULTRASTRUCTURE OF YOLK SAC, FRUIT BAT
K B Karim. W A Wirnsatt. A C Enders, A Gopalakrishna
PLATE 2
PLATE 3
EXPLANATION OF FIGURES
8 TEM view showing basal region of an endodermal cell and part of the connective
tissue (ct). Note the presence of a few protrusions and short blunt microvilli
(arrow) facing the connective tissue. bl, basal lamina. x 14,000.
9 TEM section through the mesothelial cells. Note the prominent intercellular
spaces separating the apical segments of the cells and the numerous elongate microvilli extending from the cell surfaces into these spaces and the exocoelom.
x 9,000.
10 Scanning electron micrograph showing the irregularly lobulated mesothelial cell
surface. The exocoelom (x) extends into the crypts separating the lobules. Note the
warty appearance of the mesothelial cell surfaces. x 500.
11 Scanning electron micrograph of the mesothelial cells at higher magnification.
Note the abundance of irregular shaped microvilli projecting from the apices and
lateral margins of the cells. x 5,000.
504
ULTRASTRUCTURE OF YOLK SAC, FRUIT BAT
K B Karirn, W A Wimsatt, A C Enders, A Gopalakrishna
PLATE 3
505
PLATE 4
EXPLANATION OF FIGURES
12 Electron micrograph of junction between two mesothelial cells not separated by an
intercellular cleft. Note the close apposition of t h e membrane contact between
them (arrows). x 14,000.
13 A close up of the microvilli protruding from the apex of a mesothelial cell. Note the
presence of microfilaments arranged in parallel within their interior. x 40,000.
14 Electron micrograph of mesothelial cells and part of t h e exocoelomic space. The
basal region of the cells is highly folded (arrow) and fragments of lysing cells (x)
lie within the exocoelomic space. fc, foetal capillary in the stromal conective tissue.
x 9,000.
ULTRASTRUCTURE OF YOLK SAC, FRUIT BAT
K B Karim. W A Wimsatt, A C Enders, A Gopalakrishna
PLATE 4
507
PLATE 5
EXPLANATION O F FIGURES
15 P a r t of two mesothelial cells magnified to show the distribution of free ribosomes,
microfilaments (long arrow) and microtubules (short arrow) within the cytoplasm.
Note the intimate membrane contact between cells (arrows) and a few coated vesicles (cv) in the apical cytoplasm. n, nuclei. x 30,000.
16 Mesothelial cell a t lower power showing coated vesicles and caveolae in the apical
cytoplasm and t h e basally situated mitochondria (which exhibit fixation damage).
The arrow indicates the Golgi complex. x 17,500.
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ULTRASTRUCTURE OF YOLK SAC, FRUIT BAT
K B Karim. W A Wimsatt, A C Enders, A Gopalakrishna
PLATE 5
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pteropidae, desmarest, bat, fruits, observations, microscopy, leschenaultii, indian, sac, electro, rousettus, yolk
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