THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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ce11s usually contaln either numerous membrane-bound par cles of
varying osmophì1ia or numerous rosettes of glycogen. Binucleate cells
in the 70 day trophoblast exhibit polarity; majority of their mito-
chondria and a small but often complex Golgi body are situated in that
part of the ce]1 nearest to the maternal tissues, smaì1 clear, membrane-
bound vesicles are scattered throughout the cytopìasm, and sone cells
are, in addition, filled with mu'ltivesicular bodies of varylng size
and density. Mitochondria wlth tubular or veslcular cristae, and
numerous dilated irreguiar cisternae and tubules of endoplasmic reticulurn
filled with a f'locculent material of varying densìty, are also present
ln the cytop'lasm. Aìthough cells conta.ining denseìy osmophilic membrane-
bound part'icles like those of the older cells are not present at the
70th day there are a few gl ycogen -contai ni ng cells. The binuc.leate
trophobìasts are identified by their pAS-positive properties.
The first signs of the interdigitation (implantation)
or embryonic and maternal tissues appear ear'ly in the 4th week (28 days)
of gestation. A series of ridges and grooves in which there is a close
association between the chorionic and the endometri um develops on the
maternal caruncular surface. These endometrlaì grooves, which deepen
and branch as development proceeds, are ìlned in some area by flattened
multinucleated syncytìaì mass, while other areas appear to have an
attenuated cytopìasmic covering. The syncyti al rnass was nonnaììy pAS-
positlve in appearance, aìthough not as strongly as the binucleate cells
located within the trophoblast.
At alì stages the chorionic vJlti contain vascu.larlzed
mesenchyme and are compìetely covered by cuboidal un.lnucreate trophobrastic