Early eccentricity in gravitationally oriented quail germs.

Germs in extracted white shelled quail eggs were obliquely or vertically oriented by air-bubble method (Callebaut, 1991) and further incubated. After their bilateral symmetrization we observed a parallelism between the eccentricity of the area pellucida, the aspect of the subgerminal cavity and the subgerminal yolk. Our observations suggest that at that moment the subgerminal yolk has tendency to rotate (symmetrization rotation) under the germ in a topwards direction. The subgerminal cavity extends below the lower germ wall and so the contact of the germ with the underlying yolk is disrupted in its central lower (cranial) part and there numerous free yolk masses (forming the "anti-sickle") were seen. By contrast at the upper (caudal) part of the germ no such tearing occurs. There the original subgerminal cavity ends abruptly against the anlage of Koller sickle. The Koller sickle thus develops where the most central direct contact of the germ with the subgerminal yolk persists for longer periods.