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Stage 5c specimens have an estimated postfertilization age of 11 to 12 days and a conceptus diameter of approximately 0.15 to 0.2 mm. The distinguishing characteristic at this substage is the presence of large, irregular, intercommunicating lacunar spaces that contain enough blood to form a discontinuous red circle about one mm in diameter that is visible on the endometrial surface. The rostral and caudal ends of the embryonic disc can be identified for the first time as well as the right and left sides.


Section 70

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