THE GASTRULATION OF MONGOLIAN SHEEP EMBRYOS / 解剖学报

ABSTRACT

The Mongolian sheep embryo develops into gastrula from 8 days 17 hours 10 minutes to 12 days 14 hours 30 minutes after coitus. The blastocyst is spherical in shape about 266—972?m in diameter. The zona pellucida has disappeared. The trophoblast consists of simple flat epithlium or simple cuboidal epithelium. About 8 days 17 hours 10 minutes to 9 days 15 hours 18 minutes after coitus the embryonic knot becomes spheroid, about 70—72?m in diameter. The embryonic knot is slightly protruding from The surface of the blastocyst and is covered by the trophoblast, the ectodermal cells of the dorsal portion of the embryonic knot form a mass. The lower surface of the embryonic knot has differentiated into the endoderm. The extraembryonic endoderm extends to the inner surface of the trophoblast from the periphery of the embryoblast. About 10 days 16 hours to 10 days 17 hours 20 minutes after coitus, in the dorsal portion of the embryonic knot forms a vesicle which is known as the primitive amniotic cavity about 40?m in diameter. The bottom of the primitive amniotic cavity has differentiated into the ectoderm, about 72—90?m in diameter. The endoderm of the lower surface of the embryonic knot continues to develop along the inner surface of the trophoblast to the equator. The developmental process of the primitve amniotic cavity of Mongolian sheep embryos is different from rabbit、guinea pig and human embryos, but it is similar to the mole embryos. About 11 days 16 hours 5 minutes to 12 days 14 hours 30 minutes after coitus, the embryonic knot becomes discal in shape and is fully developed, about 252—396?m in diameter. The primitive amniotic cavity of the dorsal portion of the embryonic disc has disappeared. The ecitoderm is exposed to the surface of the blastocyst, it consists of stratified columnar epthelium. The endoderm of the lower surface of the embryonic disc consists of the simple flat epithelium, it forms a spherical primitive gut cavity along the inner surface of the trophoblbst.