THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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which contain' as lvell as the organeì'les descrlbed above, elongated
cisternae of granu'lar endop'lasmìc retìculum located in the lateral
regions of the cel'rs. At the other, are smaì r numbers of cefis, usuaìry
arranged in cìumps, containing fewer shorter cisternae of granular
endoplasmic retjculum and numerous darkl y-s taì n.i ng granules, whÍch vary
in sjze, are pleomorphic in forn, and appear in some cels to be undergoìng
degenerative changes. Large granuìes may distort the nucleus. Between
these tvlo extreme cell types are found intermediate forms. At 70 days
of gestation , onìy one form of cuboidal ep.ithelial cel.l is
present. It differs from those described above in havrng numerous free
rlbosomes, short dirated clsternae of agranurar endoplasmic reticurum.
Ocassionaìly a small Golgi complex is seen, but neither the darkly_
staining granules nor the elongated clsternae of granular endopiasmic
reticulum characteristic of the mature cuboidar cens are present.
The binucleate giant cel.ls, which constitute about one_
fifth of the total trophob'last tissue, are found, usual .ty sìngly, among
the cuboida'l epithelial cells. These cells neither rest on the basement
membrane nor cont.rbute to the fetar -maternal junction. Their two rarge
rounded, nuclei have one or two smal t nucleol i and ciumped chromatin.
Mitochondria, similar to those of the cuboida.l epíthelium, are spread
throughout the cytoplasm, arthough they usualry are ress numerous in the
'lateral regions of the ceÏrs. The cytop'lasm which is denser than that
of the cuboidaì cells, contains numerous short, di.lated cisternae of
granular endoplasmic reticulum, and a large, conplex Golgl apparatus.
The plasma membrane of these ce s does not show the compìex interweavinq
or obvious desmosomes typical of the cuboldal cells. The blnucleate