The ultrastructure of spermatozoa and the changes through which they are differentiated during sperm formation in an echiuroid were observed under the electron microscope., Many spermatids are connected to one central cytoplasmic mass and the sperm differentiation proceeds synchronously in one sperm-ball. Dense platelike structures appear in the cytoplasm of early spermatids and disappear soon. In the process of nuclear condensation, many electron-dense aggregates appear in homogeneously textured chromonema and the aggregates are packed together to form a uniformly dense nucleus. Near the centriole at the opposite side from the central mass, the mitochondria fuse together to form one large middle-piece mitochondrion and the acrosomal vesicle is formed from the Golgi-complex. The differentiating acrosome in the late spermatid moves to the anterior tip of the head. In the completed acrosome, a flocculent substance accumulates in the conspicuously expanded invaginated pocket of the acrosomal vesicle and two kinds of material of different electron density fill the inside of the acrosomal vesicle. The spermatozoa remain connected to the central mass at the lateral side of the head until they become fully mature and are packed into the nephridia before spawning.In the phylum Annelida, the ultrastructural changes in spermiogenesis have been reported in some species of Oligochaeta by GATENBY and DALTON (1959), FERRAGUTI and LANZAVECCHIA (1971), ANDERSON et al. (1967ANDERSON et al. ( , 1969, and SHAY (1 972). In the class Echiuroidea, TYLER (1 965) reported briefly the ultrastructure of the spermatozoa of Urechis caupo and its changes in fertilization, but no electron microscope study has yet been performed on sperm formation in echiuroid worms.We intend to investigate the ultrastructural changes in gametogenesis of various marine Annelida, and in the present paper, we will report the process of the sperm formation as revealed by the electron microscope in an echiuroid species, Ikedosoma gogoshimense.As we reported previously (1962), the germ cells develop floating in the coelomic fluid in this worm. Male sexual cells make a cluster from the early stage 77
The age distribution of Cynops pyrrhogaster was studied by skeletochronology on 12 breeding populations inhabiting altitudes ranging from 120 m to 1140 m on Shikoku Island, Japan. In populations inhabiting altitudes 500 m or less, the mean SVL were smaller than in those that lived at higher altitudes. In populations inhabiting altitudes less than 500 m, minimum age at maturation was three years. In populations inhabiting altitudes of 500 m or more, the minimum age at maturation was four to seven years. The number of testes lobes was influenced by age and body size and was variable among populations.
In an attempt to elucidate the mechanism of production of macrocytosis in acute anemia, we studied changes in red cell volume and hemoglobin content, the RNA level of normoblasts and reticulocytes and RNA synthesis in reticulocytes of rabbits made anemic by blood loss or phenylhydrazine administration. The results were as follows:
(1) In severe phenylhydrazine anemia, red cell volume and hemoglobin content per cell increased to twice the normal values.
(2) The RNA level of normoblasts decreases with the maturation of the cells and reaches a minimum at the orthochromatic stage. The decrease is similar in the normal and anemic rabbits.
(3) The RNA level of reticulocytes in the bone marrow is higher in anemic than in normal rabbits. In general, the RNA level of reticulocytes of anemic rabbits is comparable to that of the polychromatic normoblasts, while in normal rabbits this value is comparable to that of orthochromatic normoblasts.
(4) Autoradiographs of reticulocytes incubated with H3-uridine indicate that the increased level of reticulocyte RNA of anemic rabbits is not due to newly synthesized RNA.
From these results, we conclude that in an "emergency" situation of erythropoietic stimulation denucleation of normoblasts occurs at the polychromatic stage of red cell maturation, with skipping of the terminal cell division to orthochromatic cells and formation of macrocytic reticulocytes and red cells.
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