Morphological and histochemical obervations on the ovarian balls of Centrorhynchus corvi (Acanthocephala)

Unlike in other acanthocephalans, the overian balls of Centrorhynchus corvi are complex and are composed of 24–30 ovarian ball units. Each ovarian ball unit consists of three structural and functional units – the oogonial syncytium, developing oogenetic cells and the supporting syncytium – complementary to the ovarian balls of other acanthocephalans. Three metamorphic stages of the nuclei in the oogonial syncytium are described, depending on the nuclear morphology, chromatin structure and appearance of the nucleolus. Third-stage nuclei bulge out at the periphery of the oogonial syncytium and are surrounded by its cytoplasm and a thin membrane. Ultimately these are separated from the oogonial syncytium to from oogonia containing small amounts of cytoplasmic components derived from the oogonial syncytium. Nuclei of the young oogonia, oognia at the budding stage, and 3rd-stage nuclei of the oogonial syncytium all possess nucleoli and are similar also in their nuclear dimensions and cytochemical affinities. Nuclear resemblances, and cytoplasmic similarities of the oogonia and oogonial syncytium with regard to the presence of lipids, RNA and proteins support the concept of the origin of oogonia from the oogonial syncytium.The free oogonia divide mitotically in the cellular zone where they undergo a single mitotic division and the resulting oocytes enter the prophase of meiosis. I. The meiotic primary oocytes in contrast to the permeiotic primary oocytes of other acanthoscephalans enter the growth phase which is closely accompanied by the accumulation of various ooplasmic components such as basophilic yolk nucleus which is composed of RNA, proteins, lipoproteins and phospholipids. Histochemical features of the oogonial and supporting syncytium are described.

Der Dotterkern in jungen Oocyten von Noemacheilus barbatulus (L.) (Teleostei, Cobitidae) / The Yolk Nucleus in Young Oocytes of Neomacheilus barbatulus (L.) (Teleostei, Cobitidae)

The Yolk Nucleus in Young Oocytes of Neomacheilus barbatulus (L.) (Teleostei, Cobitidae) Yolk Nucleus, Oocytes, Electron Microscopy, Noemacheilus barbatulus The yolk nucleus in the young oocytes of the freshwater teleost Noemacheilus barbatulus (L.) was investigated by electron microscopy. Yolk nuclei are only found in stage I. They consist of nucleolar substance, mitochondria and partly of dictyosomes. The nucleolar material leaves the nucleus through the pores of the nuclear membrane and gets into the juxtanuclear cytoplasm. It mainly consists of ribonucleic acid. The yolk nuclei of Noemacheilus doesn’t have any relations to the formation of yolk.

The fine structure of the yolk nucleus in oocytes of Antedon bifida (Pennant) (Echinodermata: Crinoidea)

The yolk nucleus of Antedon bifida is a large, intensely basophilic structure located in the cytoplasm of small to medium-sized oocytes. Electron microscopy reveals that this yolk nucleus is a conglomeration of hundreds of dense clumps. Each clump, which is a micrometer or two in diameter, consists of finely fibrogranular material in which are embedded ribosome-like particles. Also present in the oocyte cytoplasm are perinuclear dense granules, which may well be the precursors of the clumps making up the yolk nucleus. The yolk nucleus does not appear to participate directly in the elaboration of the yolk granules.

Aspects of the development of yolk spheres in the hen's oöcyte, studied by electron microscopy

The yolk of the hen's egg is composed mainly of proteins, lipids and water (see reviews by Bellairs, 1964; Williams, 1966). It consists essentially of yolk spheres floating in an aqueous protein medium (Grodziński, 1939; Bellairs, 1961). The raw materials from which the yolk is formed are synthesized in the liver of the laying hen and pass from there in the blood to the ovary (see reviews by Romanoff, 1960; Bellairs, 1964). Each oöcyte is enclosed in a capsule of follicle cells, and all the raw materials pass through this capsule before they enter the oöcyte. The morphological changes that take place within the oöcyte as the yolk spheres form have been described previously by light microscopists who have produced a variety of theories to explain their observations. Formerly, it was supposed that yolk arose in the so-called ‘yolk nucleus’, or Balbiani body, which lies alongside the cell nucleus, but few would subscribe to this theory now.