The occurrence and fine structure of the autonomic groundplexus in the lamina propria mucosae of the guinea-pig small intestine were studied by scanning electron microscopy after removing connective tissue elements by maceration in hydrochloric acid. Transmission electron microscopy was also performed to investigate the fine structure of the neuronal and glial elements in the autonomic groundplexus. Nerve fasciculi consisting of neuronal processes and enteroglial cell sheaths formed a three-dimensional network intercalated between blood and lymph vessels. Processes of enteric neurons ran within the enteroglial cell framework. No blind ends of nerve fasciculi were found. Terminal varicosities of neuronal processes were frequently exposed on the surface of the nerve fasciculi. The locations of these naked varicosities may represent the sites of interaction between the enteric neurons and their target tissues.

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The hepatic sinusoids of the soft-shelled turtle (Amyda japonica) were examined by transmission electron microscopy. The sinusoidal wall was composed of endothelial cells, Kupffer cells and Ito cells. The basal surface of the hepatocyte facing the Disse's space was covered by a continuous basal lamina. In addition to the Ito cells, the Disse's space contains a considerable number of smooth muscle cells. Many of these were distributed sporadically, while others appeared as a sphincter circling the sinusoid. The smooth muscle cells in the Disse's space showed the following features: 1) The nucleus was located eccentrically near one end of the cell. 2) The surface vesicles and pits, mitochondria and dense patches along the myofilament bundles were all sparse as compared with those known from mammalian smooth muscle cells. 3) Cytoplasmic processes or ruffles were protruded into the Disse's space. 4) A weak basal lamina could be recognized.
Sinusoidal endothelial cells were characterized by many large electron lucent lysosomes in their perikaryon and by small fenestrae in their attenuated cytoplasm. Ito cells sending out several cytoplasmic processes, possessed a single large lipid droplet on one side of the nucleus. A single cilium budding from the distal centriole into the Disse's space was found in an Ito cell.
Extrasinusoidal macrophages were considerably numerous in the soft-shelled turtle liver. Some of the macrophages were apparently migrating into the sinusoid, there to presumably transform into the Kupffer cells.

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The secretory activity of surface mucous cells was quantitatively studied in the mouse stomach under three different dietary conditions: ad libitum feeding, fasting for 15hrs, and refeeding 1hr after 15-hrs fast. Surface mucous cells were classified into isthmus cells, foveolar cells, surface cells and degenerating cells according to stage of maturation. The number of exocytosis and cytoplasmic granules was calculated in unit length of the apical plasmalemma for cells in each stage.
Foveolar and surface cells in fasted animals manifested higher exocytotic activity than the other two groups (P<0.01). This suggests that physical and chemical stimuli of the gastric content may greatly affect the secretory activity of the cell. Although the number of cytoplasmic mucous granules proved largest in the upper part of the foveola and less at the mucosal surface under any dietary condition, exocytotic activity did not differ significantly between the foveolar cells and surface cells. Degenerating cells very actively discharged mucus, regardless of dietary condition. It is reasonable to postulate that the cells secrete mucus in order to cover the surface and protect the mucosa from damage during degeneration.

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The esophageal epithelium of the adult salamander, Hynobius nebulosus, was studied by histochemistry, including periodic acid-Shiff (PAS), alcian blue both at pH 2.5 and pH 1.0, and alcian blue (pH 2.5)-PAS with or without neuraminidase-digestion, and scanning and transmission electron microscopy.
The epithelium was columnar in type, comprising partly pseudostratified and partly two-layered architecture; it consisted mainly of ciliated cells, goblet cells, and basal cells. The ciliated cells consisted of two types, light and dark: both types, especially the latter, frequently contained numerous small mucous granules in their apical portion. Ciliated-mucous cells were also occasionally present. Immature ciliated cells were frequently found. Goblet cells were divided into two types: Type I cells possessed electron lucent mucous granules, which frequently contained dense specific inclusions, and frequently bulged into the lumen; Type II cells had moderately electron-dense mucous granules with no inclusions and a conical apex which did not exceed the level of the lumen. The Type I cells were closely distributed throughout the esophagus, while the Type II were mainly dispersed in the cranial portion, remarkably decreasing in the caudal portion. Correlated histochemical and electron microscopic observations suggested that, in the Type I cell, mucous granules contain acid mucosubstances, while in the Type II, they possess neutral mucosubstanes, and that in the Type I cell mucous granules consist of sialic acid-containing glycoproteins and their swollen portions are more highly sulfated than the non-swollen ones.

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The three-dimensional vascular distribution and the vascular-parenchymal relationship in normal guinea pig thymus were studied by light, scanning and transmission electron microscopy. Interlobular arteries arising from one thymic artery entered the thymic parenchyma where they branched into arterioles and then formed capillary networks in the cortex and in the medulla. Most cortical capillaries drained to the surface via perpendicular venules which merged into the subcapsular veins. Some vessels of the inner cortex, however, returned blood to the postcapillary venules (PCVs) at the cortico-medullary junction and in the medulla. The vascular supply of the guinea pig thymus is thus characterized by a dual circulation in which venous blood drains either via a subcapsular or via a cortico-medullary route. The endothelium of the postcapillary venule (PCV) was flat and often contained migrating lymphocytes. These venules were surrounded by a perivascular space (PVS) which separated the vessel from the parenchyma and which contained many lymphocytes. This PVS was not lined by cells but was delimited on one side by the abluminal surface of the venular endothelium and on the other side by a thin, sheet-like layer formed by cytoplasmic processes of epithelial reticular cells. This epithelial sheet was not continuous, as there were frequent interruptions or gaps where the PVS communicated directly with the intercellular mesh of the thymic parenchyma. The PVS did not form a continuous longitudinal channel but was interrupted by epithelial trabeculae. Some macrophages and a few plasma cells were seen in the parenchyma near the PVS. These findings suggest that the PCV and the PVS in the thymus may function as pathways for the migration of lymphocytes into or out of the blood circulation.

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Cryptorchid surgery to move the testis and epididymis to the abdomen was performed in mice of 60 days of age; one week later the mice were subjected to further surgery to reposition the organs in the scrotum. The mice were sacrificed at 1 week inter valsuntil 11 weeks after the initial operation.
After the first operation, spermatozoa in the epididymal duct rapidly disappeared and were almost absent until the 4th week. Then spermatozoa appeared again, increased, and reached normal numbers by 10 weeks. With the disappearance of the spermatozoa, a PAS-positive material, which is believed to be secreted in the middle part of the head of the epididymal duct (ABE et al., 1982), was accumulated in the epididymal duct in the body and tail of the epididymis, and PAS-positive inclusions appeared in the principal cells of the duct in the body 2 weeks after the first operation. The inclusions developed in size and number during the aspermia period, then decreased in number with the reappearance of spermatozoa from the 5th week to ultimately disappear by 10 weeks after the first operation.
We have previously demonstrated that such inclusions appear also after efferent duct ligation, which interrupts the flow of spermatozoa and testicular fluid into the epididymal duct (ABE et al., 1982). Both present and previous findings indicate that the appearance of PAS-positive inclusions depends on the absence of spermatozoa in the epididymal duct irrespective of the presence of the testicular fluid in the duct. It is suggested that the PAS-positive material is utilized by spermatozoa and, in the absence of spermatozoa, is accumulated in the lumen and ingested by the principal cells of the epididymal duct in the body of the epididymis.

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The distribution of carbonic anhydrase (CA) activity was studied by electron microscopic histochemistry in rat Pacinian corpuscles, Meissner corpuscles and Merkel cell-neurite complexes using the cobalt bicarbonate method. The distribution of CA activity in these axon terminals was compared to the activity in sciatic nerve axons. An intense enzymatic CA activity was demonstrated in axon terminals of both Pacinian and Meissner corpuscles, while a weak activity was found within the axoplasm of terminals abutting Merkel cells. Some large- and medium-sized axons in sciatic nerves exhibited an intense activity. These findings indicate that large- or medium-diameter sensory axons innervating corpuscular endings have an intense CA activity extending from their somata to their sensory terminals. Axons to Merkel-neurite complexes differ in CA activity from those innervating Meissner and Pacinian corpuscular endings.

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Atria from dystrophic and non-dystrophic mice were examined by light and electron microscopy. Particular attention was paid to the granularity of the specific atrial granules and the development of the Golgi apparatus. At the light microscopic level, both a decrease in number and degenerative changes were recognized in the atrial cardiocytes, which were intercalated by increased connective and adipose tissues. At the electron microscopic level, the dystrophic atrial cardiocytes showed a variety of degenerative changes and a decreased number of granules; the impaired development of the Golgi apparatuses were noticed. A quantitative analysis revealed that the number of the granules per unit area in dystrophic cardiocytes was significantly smaller in both the right and left atria, and that the relative area occupied by the Golgi fields of the dystrophic was significantly smaller in the right atrium than in non-dystrophic controls. These findings indicate that the synthesis of atrial natriuretic polypeptide (ANP) is inhibited in dystrophic mice. It is suggested that the water and electrolyte imbalance known in dystrophic cases can be accounted for by the impaired secretion of ANP in the heart.

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Connective tissue papillae underlying epithelial cell layers of the lingual papillae of newborn mongrel dogs were exposed by long term hydrochloric acid treatment and observed by scanning electron microscopy.
Each of the filiform papillae of ovoid shape (100-130μm in diameter) contained a connective tissue papilla representing a smaller elliptical protrusion (90-100μm in length, 70-80μm in width). Its overview showed a horse-shoe shape, opening anteriorly. Its posterior curvature projected a conical node with a rounded apex.
Each of the fungiform papillae (150μm in diameter) contained a connective tissue papilla of rounded shape (100μm in diameter) whose upper surface was facetted with several slight depressions.
The entire surface of the connective tissue papillae was found to be covered by networks of collagenous fibers of varying thickness, running in various directions.
The basal surface of the epithelium revealed regularly distributed round holes that corresponded to the connective tissue papillae. In the filiform papillae, a small elliptical bulge was seen on the anterior side of each hole.
Light microscope observation indicated that the anterior column of the filiform papillae contained a granular layer with moderate keratohyaline granules, whereas the posterior column did not show such a granular layer.

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Fat-storing cells in the liver of an adult Schneider's skink were investigated by means of transmission electron microscopy. The fat-storing cells were localized in the perisinusoidal space or in the hepatic “recessus”. They revealed a single cilium originating from one of the paired centrioles and projecting into the perisinusoidal space. The functional significance of a single cilium in the fat-storing cell is still unclear.

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