Blood vascular casts of rat ovaries were prepared by injection of a low viscosity methacrylate medium, and observed by scanning electron microscopy. The proper vascular pattern of the rat ovarian follicle starts as a basket-like wreath of fine capillaries around the primary follicle. As the follicle grows larger, the wreath becomes more developed. The fully developed wreath around the Graafian follicle consists of sinusoidal capillaries. In ovulation, the apical area of the wreath is opened and the basal area of the wreath is elevated. After ovulation, the wreath shrinks and its opened area is closed, with markedly dilated vessels directly continuous with the arterial capillaries. The wreath then transforms, by intense new formation of capillaries, into a conglomerated sinusoidal capillary plexus with an avascular area within it. The avascular area soon disappears by continued intense formation of capillaries in the plexus, and a complete and dense vascular network of the corpus luteum is formed. The capillaries of the fully developed corpus luteum are small in caliber and not sinusoidal in nature. Discontinuities of the capillaries and a flattening of the efferent branches are the initial signs of the degeneration of the corpus luteum. The small markedly degenerated corpus luteum contains only scattered thready capillaries. The corpus albicans contains few blood vessels.

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Intercellular junctions in pancreatic acinar, duct and endocrine cells were studied by thin section and freeze-fracture methods in developing rats and mice. Undifferentiated cells were joined by the zonula occludens and isolated fragments of tight junctional strands. Small gap junctions were either occasionally associated with tight junctional strands or appeared independent of them. During the morphological differentiation of acinar cells, strands of the zonula occludens developed to form a complicated meshwork while gap junctions rapidly increased in size. Duct cells were joined by the less-developed zonula occludens but gap junctions were rarely seen. In the neonate, intercellular junctions were similar to those in adult acini and intercalated ducts.
Endocrine cells were joined by maculae occludentes and small gap junctions. During late prenatal days, the macula occludens increased in size and gap junctions in number. Sometimes tight junctional strands disappeared to leave membrane elevations, some of which were associated with small gap junctions. Maculae occludentes on endocrine cells were gradually fragmentized and diminished during postnatal development. They were completely lost in the rat.
These results suggest that intercellular junctions play important roles in pancreatic development. In particular, the transient development of maculae occludentes is associated with endocrine cell development, and intercellular communication mediated by gap junctions may be important for the differentiation of acinar and endocrine cells.

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Mechanisms involved in the removal of exogenous macromolecules from circulating blood were investigated in the aglomerular nephrons of the kidney of the sea-horse, Hippocumpus kuda Bleeker, using either native anionic or cationized probes.
After intraperitoneal injection of native anionic horse-spleen ferritin (HS-AF) or cationized one (HS-CF) into the sea-horse, kidneys and gills were examined morphologically at intervals of 1 h to 14 days. Histochemical and immunohistochemical studies and transmission electron microscopy of the kidneys revealed that most of the injected HS-AF or HS-CF were taken up by macrophages in the sinusoids of hemopoietic tissue through pinocytosis, being gradually accumulated into their phagolysosomes. By the 14th day, the injected ferritin particles were degraded and the ferric agglomerates were concentrated within the phagolysosomes. Then the macrophages heavily laden with densely packed ferric catabolites migrated into the hemopoietic area forming macrophage agglomerates or macrophage centers. Some HS-AF and HS-CF particles infiltrated into the tubular basement membrane, where they were taken up by the tubular epithelial cells through pinocytosis, translocated into the phagolysosomes, fragmented into small ferric catabolites and then excreted into the urinary space.
In contrast, examination of the gills revealed neither HS-AF, HS-CF particles nor their histochemically detectable ferric catabolites in either the interstitial space including basal lamina or the alveolar epithelia. It seems that no appreciable egress of exogenous substances occurs from the gill into the environmental water.

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This study reveals the presence of small granule-containing cells in the heart of the toad, Bufo melanostictus. The cells were small in size (5-25μm in diameter) and located in the interatrial septum. The small cells occurred singly or in small clusters within the cardiac ganglia or near the myocardial cells. They were characterized by numerous large dense core vesicles (80-300nm) in their cytoplasm. With 5-hydroxydopamine treatment, the granularity of the large dense core vesicles was greatly intensified. The large dense core vesicles were variable in size and shape and extended into the long and short processes of the cells. Some of these processes were in close contact with myocardial cells. Other cytoplasmic organelles included rough endoplasmic reticulum, free ribosomes, randomly distributed mitochondria and glycogen particles. Individual cells or cell clusters were usually ensheathed by a thin layer of cytoplasm from sheath cells. The small granule-containing cells in the present study correspond to the catecholamine-containing (SIF) cells described by earlier workers. These cells presumably regulate muscular and ganglionic activities by virtue of their close association.

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Topographical changes in the development of the principal part of the supraoptic nucleus (SON) of the rat were studied by analyzing its tridimensional images, from the intrauterine to the senescent stage. Evaluation of the growth rate of the SON was also made possible by this procedure. From the onset of the appearance of the SON, changes in its spatial orientation were marked by a progressive increase in the antero-posterior and medio-lateral dimensions. The ventro-dorsal one increased up to 6 months of age and then began to decrease progressively. These changes were accompanied by a ventral displacement that became indistinct at 6 months, whereas the lateral migration persisted. No rostro-caudal displacement was recognized. Possible reasons for these changes are briefly discussed.

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A morphological study of the lymphatic system in atrioventricular (AV) valves of adult dogs and puppies was carried out using a series of techniques including India ink injection, a hydrogen peroxide technique, light microscopy, and electron microscopy. Lymphatic capillaries were found in all cusps of the AV valves, and were shown to extend delicate networks in the subendocardium of the atrial side of the valves. The extent of their development varied among cusps, being most prominent in the anterior cusp of the mitral valve. Marked differences were noted in the intravalvar distribution between lymphatic capillaries and blood microvessels. The ultrastructures of the lymphatic capillaries in the AV valves were also demonstrated.

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In order to demonstrate the occurrence of cytoplasmic filaments and their relationship to secretory granules, rat anterior pituitaries perfused with a detergent solution containing 0.5% Triton X-100 were observed with the scanning electron microscope. Thin section images and quick-freeze, deep-etching replica images were also studied. Scanning electron microscopy clearly demonstrated complicated networks of numerous cytoskeletal filaments in the cytoplasm of all the secretory cells of the anterior pituitary. These filaments can be classified into two groups on the basis of their diameter: thick filaments measuring 30-40nm in diameter, and thin filaments 15-25nm in diameter, each including the thickness of the platinum coat. The thick filaments, which run rather straight, are considered to be microtubules. The thin filaments attached to the surface of a secretory granule may connect it with an adjacent secretory granule, with cytoorganelles, with the nucleus, or with the plasma membrane. Transmission electron microscopic images of thin sections and quick-freeze, deep-etching replicas confirm the occurrence of filamentous structures associated with the limiting membrane of the secretory granule. The fine filaments associated with the limiting membrane of the secretory granule might participate in the support and transport of the granule.

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The taste buds and their nerves in the guinea pig were immunocytochemically investigated with regard to the localization of spot 35 protein, neuron-specific enolase (NSE), neurofilament protein (NFP), and S-100 protein. The spot 35 protein-like immunoreactivity was confined to slender cells comprising half the number of taste bud cells. NSE-like immunoreactivity was recognized in some taste bud cells as well as nerve fibers both within the taste bud and in the subepithelial connective tissue. The NSE-immunoreactive cells were divided into two cell populations: one weakly and the other intensely immunoreactive. The former cells proved to be spot 35 protein-immunoreactive. Moreover, the cells immunoreactive for both spot 35 protein and NSE were frequently associated with nerve fibers immunostained intensely for NSE. The NFP- and S-100 protein-like immunoreactivities were found in none of cells in the taste bud, but exclusively in the subepithelial neural elements.

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