The locus coeruleus (LC) of rats at different ages was studied in sections stained by the Golgi-rapid method. The LC is composed of two types of neurons, medium-sized (20μ×35μ) and small cells (10μ×15μ). The medium-sized cells are mainly fusiform in shape and occupy the dorso-caudal part of the nucleus, while pyramidal or multipolar cells frequently occur in the ventral part. Both types of cells bear a moderate to large number of spines on the surface of their soma, which form the main criterion for identifying the LC neurons. Though they radiate several relatively short dendrites in different directions, which bifurcate once or twice, the medio-ventral ramification is prevailing, extending beyond the limit of cells to the pontine central gray adjacent to the LC. The latter region might constitute the principal receptive sites of LC for inputs from various origins. Axons of LC neurons take their initial course either latero-rostral- or latero-caudalwards, while some axons divide dichotomously rostral- and caudalwards. Fine axon collaterals are frequently demonstrated within the LC and sometimes seem to contact with dendrites of LC neurons. Besides this, two kinds of afferents of unknown origins are observed between LC neurons. At least three kinds of small oval neurons are occasionally impregnated, though their axonal distributions cannot be demonstrated.

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The livers from normal bats captured in summer and autumn (active period) and in winter (hibernating period) were electron microscopically examined with reference to the worm-like bodies.
1) The worm-like bodies were numerous in bats captured in the active periods, while they were few in hibernating bats. The development of this body varied considerably from cell to cell.
2) The worm-like body seemed to develop from a short and straight tubular invagination of the plasma membrane, whereas the fully developed unit of the body comprised a twisted and complicatedly branching tubule extended in the cytoplasm, the end of which seemed to be retained as the orifice to the extracellular space. The contents of the tubule continuous with the cell coat showed faint transverse striation and a median dense line. A large worm-like body was presumably composed of a number of the units tangled complicatedly with each other, showing a large accumulation of abundant profiles of closely packed tubules. In some Kupffer cells a long tortuous tubule with a median dense line penetrated the cytoplasm transversely and communicated at both ends with two opposite surfaces facing the sinusoid.
3) The cytoplasmic area of the worm-like bodies was almost completely devoid of organelles; no communication between the worm-like bodies and other organelles was recognized. This finding suggested the resemblance of the area of the worm-like bodies to the ectoplasm. This assumption also was supported by frequent occurrence of large coated vesicles along the worm-like bodies often communicating with them.
4) The worm-like bodies did not show any signs of enlargement even in Kupffer cells ingesting blood cells in their phagocytic vacuoles. Their profiles were found abutting on the phagosomes, but direct communication between both structures was not found.
5) It was proposed in this study that the worm-like bodies might possibly represent a membrane reservoir and contribute to the enlargement of the Kupffer cell surface.

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The hypophysis of the common freshwater goby, Rhinogobius brunneus, accompanying gonadal maturation, was studied light microscopically to determine the cell types by the aid of the administration of antithyroidal and antiadrenocortical drugs. It is peculiar in that the hypophysis is entirely buried in the hypothalamus, and that the entire adenohypophysis is covered with a thin layer of the neurohypophysis.
Two types of cells, azocarminophil prolactin cells and PbH-positive adrenocorticotrophs, are discernible in the rostral pars distalis. The proximal pars distalis consists of three types of cells: weakly AF positive thyrotrophs, strongly AF positive gonadotrophs and orangenophil somatotrophs. In spite of the application of several stainings, only one cell type, the PbH-positive cell, is demonstrated in the pars intermedia.

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Parietal cells in the rat gastric mucosa fractured by freeze cracking methods under resting (control) state and tetragastrin stimulation were studied by field emission scanning electron microscopy. The structures thus revealed were compared with those studied by transmission electron microscopy.
In the fractured cytoplasm, intracellular canaliculi lined by numerous microvilli invaginated deeply towards the basal cytoplasm. Tubulovesicles appeared as many small holes of about 0.05μ in diameter and were distributed predominantly in the apical or pericanalicular cytoplasm. Some tubulovesicles directly opened into the secretory canaliculi. Occasionally, tiny microvilli appeared in tubulovesicles.
After being stimulated for 30min with tetragastrin, the secretory canaliculi of parietal cells became enlarged and there was a concomitant increase in both the number and size of microvilli. Tubulovesicles also were increased in size and number and the tiny microvilli in them were also increased. The tubulovesicles were enlarged presumably as a result of membrane fusion between contiguous tubulovesicles. It was found that the enlargement of the secretory canaliculi was the result of fusion of the membrane of a single tubulovesicle or a confluence of tubulovesicles to that of the secretory canaliculus and the successive disappearance of the fused membrane.

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Tooth germ derived from the mandible of newborn mice was used in this study. The enamel organs were dissected and attached directly to coverslips without using the plasma clot. By this method it was possible, for the first time as far as is known, to attain preparations in which the major part of the outgrowth from the explant consisted purely of epithelial-like cells which probably were ameloblasts. Abundant desmosomes and tonofilaments were confirmed by transmission electron microscopy.
Under the scanning electron microscope this outgrowth of epithelial cells revealed characteristic intercellular connections which were divided into four types. 1) In the part nearest to the explant, cell boundaries were indicated with a large number of short microvilli. 2) In the zone beyond the first type, the intercellular connection was represented by bridge-like processes firmly combined with each other. 3) In a still further zone, the tips of bridge-like processes were free from the cell connection and extended to the adjacent cells with the advance of cell migration. 4) In the most peripheral part of the explant, the cytoplasmic processes were capable of further expansion. These cells were soon separated from the adjacent cells to migrate as free cells.

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Microtubules were identified in the subsarcolemmal area of smooth muscle cell in the taenia coli of guinea-pigs. They may traverse myofibrils but more frequently they run parallel with the long axis of the cell. The microtubules were often in contact with sarcolemmal caveolae. A caveola appeared to contact with an end of a microtubule or with the outer membrane of a mitochondrion. Occasionally a long mitochondrion was located between two evaginations of sarcolemma. The direct contact of caveolae with a mitochondrion was typical in such long mitochondria. Granular and agranular sarcoplasmic reticulum (SR) were also in the vicinity of mitochondria. The SR was in contact with mitochondria and also with vesicles. Subsarcolemmal mitochondria were often in continuity with agranular SR or invaginations of sarcolemma.
Low evaginations of sarcolemma appeared to be a cell contact device but nexas-like interdigitations, protrusions from the dark cell into the light cell, were also evident.
These morphological findings may suggest a potential network of transport or conductance in this type of smooth muscle.

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The fine structure of the ellipsoid of the cat spleen was studied by electron microscopy.
The ellipsoid consists of closely packed reticular cells and fibers, and macrophages around a capillary. The macrophage cytoplasm contains phagocytized red blood cells within cytoplasmic vacuoles. The endothelial cells are specifically high in the lumen surrounded by an incomplete basement membrane.
Two types of filaments are revealed within the endothelial cell cytoplasm. Thick filaments, 100Å in diameter, are found in almost any part of the cytoplasm and show a tubular structure in cross section. They are thought to be cytoskeletal in function. Thin filaments, 60Å diameter, are seen as electron-dense patches in the basal area of the cytoplasm. Their possible contractile function is discussed.

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The capillary endothelial pores of perfusion-fixed and immersion-fixed liver, thyroid and adrenal of mice were observed using freeze-etching preparations. In liver sinusoids, endothelial pores are heterogeneous in size and range from 50-100nm. When the pores are classified into three types according to their size, small pores up to 100nm in diameter represent 69.8%, intermediate pores measuring 100-500nm 27.6% and large pores exceeding 500nm 2.6% of all pores in number. The endothelial pores of the thyroid blood capillaries are fairly homogeneous in size (70-90nm), corresponding to the small type pores in the liver. In both adrenal cortex and medulla, the capillary endothelial pores measure 40-50nm in diameter, showing small and intermediate types. In the adrenal cortex the former occupy 80.6% of all pores and the latter 19.4%. No larger type pores are recognized in the adrenal gland. These findings are not affected by different fixation methods, either perfusion or immersion.

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