Ultrastructure of the ovarian germ cells in the quail embryos, with special reference to the oocytes

Developing germ cells from oogonia to oocyte stages in embryonic quail ovaries were observed ultrastructurally. In contrast with those of chicks, quail oocytes showed some conspicuous structures. Typical feature of the Balbiani body, which was constructed by eccentrical concentration of whole organelles, was observed through the oocyte stage, although loose aggregations of organelles were found even at the oogonial stage. Such striking feature of Balbiani body was not observed as yet in any animal species. Golgi apparatus, which occupied the center of a Balbiani body, was often found attaching with the nuclear membrane. This finding suggests that the Balbiani body play some role for the oocyte maturation. Upon the nuclear membrane of oocytes, a great number of electron dense structures were found. They were thought to be a kind of nuclear pore complexes. Such abundance of the nuclear pore complexes was another structural characteristic of quail oocytes. They increased in number according to the progress of embryonic development, although small numbers were also seen even at the oogonial stage.