A modified freeze-substitution process is described which gives a low percentage (less than 5 per cent) of preparations of invertebrate eggs which appear to be ice crystal-free at the resolution of the electron microscope. The mitochondria show no membranes in these preparations but can be recognized by internal spaces with the size and the distribution of the cristae. The Golgi bodies resemble those seen with diffusion fixatives, but the limiting membranes are here double; that is, they appear to be a triple-layered sandwich with two outer dark approximately 25A layers and an inner light layer of the same thickness. The endoplasmic reticulum is clearly present and resembles that seen with diffusion fixatives. Here again, the limiting membranes are double with the same dimensions as those in the Golgi bodies. The membranes of the Golgi bodies and ER are seen after permanganate but not lead hydroxide staining. The hyaloplasm (or "cell sap") is crowded with 150 to 200A particles and these are also seen lining the ER membranes. In general, the structures as seen with the present technique show considerable similarity to those seen with diffusion fixatives.

Animals↗

PubMed1960

Aster-associated particles in the cleavage of marine invertebrate eggs.

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Animals↗

PubMed1957

Nuclear changes during spermiogenesis in a pulmonate snail.

Changes in both external form and internal arrangement of nuclear material have been investigated in the differentiation of the sperm of the pulmonate snail, Otala lactea. Sperm head differentiation begins with a flattening of the previously spherical nucleus and a thickening of the nuclear envelope covering the anterior and posterior surfaces of that nucleus. Tail filaments can be seen in the cytoplasm at this time. At a slightly later period the mitochondria begin to form the tail filament sheath and at this time the nucleus begins to elongate in a direction parallel to the future axis of the sperm. At the same time the nuclear material begins to orient itself at right angles to the nuclear surface which lines the pit occupied by the centriole. As nuclear elongation proceeds, this orientation of nuclear substance takes on the appearance of 60 A thick sheets bent in a direction parallel to the sperm axis. Soon the sheets fill the entire nucleus. The nucleus then begins to twist along its axis so that it starts to take on the mature, flame-shaped form. At this time the flat sheets begin to disappear and in the mature sperm head they are no longer visible (see Text-fig. 2 B).

Animals↗

PubMed1956

Electron microscopy of basophilic structures of some invertebrate oocytes. II. Fine structure of the yolk nuclei.

RNA containing yolk nuclei from the surf clam Spisula solidissima have been studied with the light microscope and with the electron microscope. A variety of structures can be seen with both and a correlation can be made between bodies studied with the electron microscope and those studied with the light microscope. The electron microscope shows many of these structures to be composed of double walled lamellae arranged in space, in various ways. The variety of patterns seen with the electron microscope can be satisfactorily explained on the basis of a hypothetical model. The presence of yolk platelets within the yolk nuclei lends support to classical observations on the synthesis of yolk within yolk nuclei or yolk nuclei derivatives. Small granules (about 100 A) are included within the double walled lamellae and their presence probably accounts for the basophilic nature of the entire body. The presence of small granules attached to electron-dense layers relates the yolk nuclei described here to ergastoplasm discussed by others.

Animals↗

PubMed1956

Electron microscopy of basophilic structures of some invertebrate oocytes. I. Periodic lamellane and the nuclear envelope.

Highly basophilic plate-shaped regions from oocytes of the surf clam have been examined with the electron microscope. The regions are composed of flat, hollow vesicles perforated by pores arranged, in surface view, in a hexagonal pattern. Cross-sections of this structure show a periodicity consisting of loops (cross-sections of the continuous space within the vesicle) alternating with spaces partly filled with dense material (pores). These structures are shown to resemble closely, the nuclear envelope. Similarities to and differences from basophilic regions of other cells are discussed and it is suggested that the small granules of Palade (38) are represented by granules composing the walls of the annuli of the nuclear envelope and assumed to be present in the annuli of the vesicles. Because of differences in the structure of these regions from basophilic regions of other cells, the name periodic lamellae is suggested since the structures show periodically repeating substructures (annuli) in both cross-sections and surface views.

Animals↗