1. Carnegie Inst, Wash. Pub. 525;Heuser;Contrib. Embryol,1941
2. Carnegie Inst. Wash. Pub. 363;Streeter;Contrib. Embryol,1926
3. Zur Kenntnis der Trophoblastschale bei jungen menschlichen Eiern
4. An Early Ovum Imbedded in the Decidua;Bryce,1908
5. Carnegie Inst. Wash. Pub. 525;Hertig;Contrib. Embryol,1941