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Formation of germinal granules during oogenesis was studied in sea cucumbers, Apostichopus japonicus, Selenka, 1867, using transmission electron microscopy. It was found that within the early oogenesis mitochondria interact with a Balbiani body, gradually become immersed into its substance and transformed into electron-dense structures, which are similar to the germinal granules of metazoans. In late oogenesis, formed germinal granules lose their contacts with a Balbiani body and are localized in the cortical portion of the oocyte, near the cell membrane. Vestigial mitochondrial cristae are a typical feature of germinal granules. The obtained data suggest that the process of transformation of mitochondria into germinal granules is one of the functions of the Balbiani body, whose role still remains unexplained.

This study examines the effects of selenium in concentrations of 0.01, 0.5, 1, 5, and 10 mg/liter on the growth and ultrastructure of the microalga Dunaliella salina. Selenium in concentrations of 0.01 and 0.5 mg/liter stimulated cell population growth, while the number of ultrastructural alterations was the same as in the control cells. At a selenium concentrations of 1 mg/liter, cell population growth slightly decreased by the end of the experiment, and there was some increase in the number of cells with damaged organoids and in the number of completely destroyed cells. As well, the excretory function of cell vacuoles was suppressed, and the autophagic activity of these vacuoles was activated to destroy the cytoplasm and nucleus. Concentrations of 5 and 10 mg/liter were toxic to D. salina, suppressing cell population growth and promoting extensive destructive changes. The threshold concentration of selenium for D. salina was 1 mg/liter, which is 1000 times greater than the maximum permissible concentration (MPC). The fact that the microalga was able to survive for several days in this concentration is indicative of its high resistance to selenium.

The ultrastructural mechanism of postspawning sperm resorption in the testes of the sea urchin Strongylocentrotus nudus is described. Two types of phagosomes (containing sperm and containing residual bodies) are formed in the cytoplasm of nutritive phagocytes. The phagosomes fuse with electron-dense globules, and their contents are gradually destroyed. Afterward, phagosomes are transformed into electron-transparent vacuoles, which are finally compressed by the surrounding cytoplasm.

The process of the destruction of nonreleased spermatozoa was studied using TEM in the postspawning gonads of the chum salmon Oncorhynchus keta and the pointhead flounder Cleisthenes herzensteini, as representatives of monocyclic and polycyclic fishes respectively. It was shown that in both species residual sperm cells are destroyed through fragmentation of chromatin and the entire cell. It is supposed that the process of destruction in this case is connected with autolytic disintegration known in some multicellular animals, but never described for Teleostei.

The process of resorption of spermatozoa is described in the testes of the starfish Asterina pectinifera. It is shown that the mode of resorption of the male gametes in this species is different from that in the starfish Asterias vulgaris (see Walker [17, 18]), A. amurensis, and Aphelasterias japonica (see Kas’yanov et al.

The development of male gametes (spermacia) in the red alga Gracilaria verrucosa has been studied using methods of transmission electron microscopy. Early spermatangia located along the wall of the conceptacle show an elongated shape in the thin sections. In the central part of the electron-dense cytoplasm of these cells there is a nucleus; numerous fibrous vesicles are arranged in the periphery. During the process of differentiation, the spermatangia become more rounded in shape and a large spermatangial vesicle is developed. The subsequent development of spermatium is accompanied by polarization of the spermatangium and the subsequent excretion of the spermatangial vesicle. The spermatia are oval cells containing a nucleus and fibrous vesicles. The process of differentiation of male gametes in G. verrucosa does not differ from that in five species of the genus Gracilaria, where it has already been studied. However, any conclusions about the degree of similarity between the spermatia in all the studied species can be made only after a detailed comparative analysis of the ultrastructural characteristics of these gametes.

Literature data on the structure and origin of material of the germ cell line determinants and on the presence of products of nuclear and mitochondrial genomes in the structured germ determinants (nuage) are reviewed. The personal data, obtained on spermatogenic cells of sea urchin and of other marine invertebrates, evidence the transformation of the mitochondrial matrix into the nuage material. The presence of matrix structures of mitochondrial origin in the germ plasm, which ensure reproduction and the function of the structured macromolecular complex of germ determinants relatively independent from the nuclear genome, is suggested.

The relationships between germinal bodies and mitochondria were studied in the holothurian Apostichopus japonicus and the flounder Pleuronectes asper using TEM. In the gonial cells of both species the mitochondria are arranged around germinal bodies and are in contact with the latter. A gradual disappearance of the outer membrane is found in the mitochondria that interact with the germinal substance. Later on, dispersion of the globules of the mitochondrial matrix containing mitochondrial cristae occurs. It is supposed that the substance of the mitochondrial matrix takes part in the development and functioning of the germinal plasm in both invertebrates and vertebrates.