Abstract Eggs and oocytes from the sea urchin Brissopsis lyrifera were examined with the electron microscope. In the cytoplasm of the female gametes new types of granules were observed. The possible role of these granules is discussed.
Abstract A survey has been made of the fine structure of the mesenterial filaments of starved specimens of Bolocera tuediae, a large macrophagous sea anemone; both histochemical and electron microscopical methods have been used. The cnidoglandular tract is dominated by nematocysts and by several types of granule-containing secretory cells, which are described and illustrated. The results are compared with conditions in the gastroderm of the class Hydrozoa.
Abstract Experiments in which oocytes were inseminated with heterologous spermatozoa showed that Qocytes are susceptible to the same species of sperm, as are the ripe eggs. Immediately after the spermatozoon has entered an egg or an oocyte, material appearing dark in the phase contrast microscope is ejected from the maternal nucleus; a ring-shaped corona is formed around the nucleus. No aster formation takes place in oocytes which have not yet developed the cortical reaction.
The effects of mono-, di-, and tricycfic aromatic hydrocarbons on the early development of Paracentrotus lividus were studied. In the light microscope effects were registered as inhibition of differentiation and formation of abnormal larvae with excess mesenchyme. With benzene, acridine, and aminoacridine cell separation and rapid disintegration of the embryos were observed, whereas with acridine orange the embryos developed into active larvae with a characteristic abnormal appearance. In the electron microscope weak effects were studied such as more distinct yolk granules than in the control. An increase in the number of lipid droplets was observed after treatment in phenanthrene and low concentrations of acridine orange. In the presence of acridine orange and Azur A the yolk granules appeared as more or less empty vesicles.
Abstract Eggs from 16 species of sea urchins were studied in the electron miscroscope. The jelly coat was present in several of the species, and a hyaline layer was observed between the jelly coat and the actual surface of the egg. As an inner boundary of the jelly coat a membrane was often present. The structure of the cortical granules appeared to be species-specific, and its possible use as a taxonomic character is discussed. At insemination the cortical granules were observed to break down completely before the formation of the hyaline layer and the fertilization membrane. As the events following insemination seemed to be the same for all the species studied, the actual structure of the cortical granules cannot be of importance for these processes.
Abstract Isolated blastomeres from young larvae of Echinocyamus pusillus and Psammechinus miliaris were studied by means of time-lapse cinematography. The isolated mesomeres and macromeres cleave at about the same rate as in situ in intact larvae. It was found that single meso- and macromeres were able to develop into blastulae. Isolated micromeres cleave somewhat more slowly than the micromeres in situ and as isolated cells they were not able to pass through more than three cleavages. They are characterized by the sending out of cytoplasmic protrusions. The rate of cleavage is different for meso-, macro- and micromeres and the meso- and macromeres cleave, both in situ and as isolated cells, considerably faster than the micromeres. Owing to the different rates of cleavage during the blastula stage the cells of the prospective ectoderm multiply more rapidly than the cells, which later form the endoderm and mesoderm and therefore the early development is characterized by an “animal” trend. Even minor changes in the rate of cleavage, for instance a retardation of the mesomeres, may therefore later on in the course of differentiation result in so-called vegetalization.
