Unequal caudocephalic ooplasmic uptake and eccentric formation of the subgerminal space below unincubated quail blastoderms presenting a Koller's sickle.

By radioactive ooplasmic yolk layer labeling during late oogenesis, we demonstrated that below unincubated quail blastoderms the subgerminal space extends much more peripherally in the cranial then in the caudal direction, where it ends abruptly against Koller's sickle. Our autoradiographic and histochemical investigations indicate that Koller's sickle develops by a progressive local colonisation of the centro-caudal subgerminal ooplasm, which does not take place in the cranial diametrically opposite anti-sickle region. The deep paracentral uptake of voluminous ooplasmic areas by large encircling extensions of its cells is a characteristic feature of the sickle region.