Liver fine structure was studied in various groups of vertebrates to reveal intrahepatic nerves. Nerve fibers were found in the connective tissue of the liver in all mammals, birds, and reptiles studied (Japanese monkey, crab-eating monkey, rabbit, guinea pig, rat, golden hamster, pigeon, Japanese quail, and turtle, Pseudemys scripta). Nerve fibers also made direct contact with hepatocytes in these animals except for the rat and the golden hamster. Intrahepatic nerves were rare or absent in amphibians (Rana catesbeiana and Cynops pyrrhogaster pyrrhogaster) and fishes (Anguilla japonica and Misgurnus anguillicaudatus).
The livers of mammals and birds consisted of hepatic lobules and interlobular connective tissue carrying a portal triad. The liver of lower vertebrates was a simple mass of hepatic cell cords and contained relatively small amounts of connective tissue. The increased number of intrahepatic nerves appears to be correlated with the development of higher organization of liver structure and a concomitant increase in the amount of connective tissue.

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The morphology of the juxtaglomerular apparatus of the rat kidney was investigated by scanning electron microscopy of the freeze-fractured tissue. The macula densa cells have a dome-shaped apical surface abundantly provided with short microvilli. Their basal and lateral aspects may show labyrinthine spaces which are consistently more developed than in the epithelium across the tubular lumen. The Goormaghtigh cells display the well known complex pattern of cytoplasmic extensions forming the lacis. Fractured juxtaglomerular cells show distinct nuclei and well defined secretory granules. The well developed labyrinth of the macula densa suggests a considerable trans-epithelial fluid transfer at this level.

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In a 67-day-old female kitten, the morphological differentiation of the hepatic parenchyma has been electron microscopically examined. 1) In spite of the advanced ultrastructural differentiation of the hepatocyte, the usual location of the Golgi complex to the apical cytoplasm around the bile canaliculus has not yet been established. Numerous mitochondria are mingled with round microbodies characterized by a marginal plate and a crystalloid core. Tubular cisternae of the SER occur only around the microbodies and lack within the accumulation of glycogen α-particles. 2) The sinusoidal lining has been fully differentiated and is composed of the“cytoplasmic processes”and the“sieve plates”whose fenestrae average 1300Å in diameter. 3) Kupffer cell shows an active phagocytosis to blood cells. The fuzzy coat is unsatisfactorily preserved. The cytoplasm occasionally shows short segments of a worm-like body. 4) The fat-storing cell (FSC) contains a small amount of lipid droplets which mostly appear within the dense accumulation of glycogen β-particles. Also empty FSCs devoid of lipid droplets mostly possess glycogen accumulations. The glycogen accumulations enclosing lipid droplets are closely juxtaposed by cisternae of the RER and mitochondria, suggesting the possible involvement of these organelles as well as glycogen in the lipid synthesis in the FSC. In most FSCs, abundant cisternae of the RER are dilated and filled up with a finely flocculent material, suggesting an active production of collagen precursor. The FSCs possess abundant microfilaments and microtubules. A single cilium is issued into the Disse's space from one of the paired centrioles located in the Golgi area. 5) The Disse's space of the kitten contains, besides FSCs, plasma cells and macrophages. The latter agree in ultrastructure with the Kupffer cells and are assumed to be transformed into them by being incorporated in the endothelial lining of the sinusoid.

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After injection of horseradish peroxidase (HRP) into the commissural area in the border region between areas 17 and 18, the lateral part of area 19 and the lateral suprasylvian area (LS) of cat's visual cortex, HRP-labeled neurons were distributed preferentially in layer III in each cortical region of the other hemisphere. Layer I was free from labeling in each cortical region. There were some areal differences in the distribution of labeled neurons in other layers. In the area 17/18 border region, a significant population of labeled neurons was found in the upper layer IV. The labeling of neurons in deeper layers (V and VI) increased in area 19 and further in the LS. There was no great difference in the laminar distribution between neurons which appeared after HRP injections into the homotopical region and those after heterotopical injections on the other side.
The commissural area, 17/18 border region and the LS, contained in layer III a larger number of medium-sized to large neurons than acommissural area 17 on the splenial gyrus, where layer III was filled with densely packed small neurons. The size distribution of layer III was unimodal with a marked skew towards the larger value in each cortical region. About 50% of labeled neurons in layer III were distributed in a narrow range at the border of two categories of cell sizes, viz small and medium-sized to large. Among the labeled neurons in layer III, 34.2-47.1% had larger cell sizes. Some of the smallest neurons in layer III were also labeled, however, they appeared only after HRP injections into the homotopical region of the cerebral cortex on the opposite side.

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There are three possibilities concerning the mechanism of increase in number of gonadotrophs in the anterior pituitary after castration: one is the cell division by mitosis of matured gonadotrophs, another is the differentiation of immature cells, and the third is conversion of some other cell types into gonadotrophs. In order to determine the above possibilities, light and electron microscopic examinations using a combination of immunocytochemistry and autoradiography were performed. Normal and castrated adult male rats were used. Morphometry indicated that a highly increased population of gonadotrophs reacted with anti-LHβ serum after castration. Increased numbers of mitoses and elevated incorporation of ³H-thymidine into the nuclear chromatin were observed in both anti-LHβ reactive cells and other pituitary cells after castration. Electron microscopic immunocytochemical observations demonstrated the presence of immature cells with a few immunoreactive secretory granules in the castrated pituitary. It is considered that mitosis is a major factor for proliferation of gonadotrophs in the anterior pituitary after castration, but the possibility of differentiation from immature cells into gonadtrophs cannot be ruled out. The third possibility could not be proven in this study.

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The extraregional occurrence of saccus vasculosus tissue was observed in the neurohypophysis of several specimens of three species of plectognath fishes, Fugu niphobles, Fugu poecilonotus and Canthidermis rotundatus. The ectopic tissue occurred as a compact multitubular structure in the posterior portion of the pars nervosa, either being buried in it or attaching to its dorsal margin. Scanning electron microscopy revealed that ectopic crown cells of F. niphobles were distributed further in the ependymal layer of the infundibulum. A possible route of these crown cells to the neurohypophysis was discussed with special reference to the close anatomical relationship between the neurohypophysis and the saccus vasculosus in the embryonic stage.

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The pancreatic endocrine cells of the ray, Dasyatis akajei was studied by aldehyde-fuchsin-Masson-Goldner's staining and by immunohistochemical methods. The pancreatic endocrine cells of the ray do not form islets but represent the most primitive distribution among elasmobranchs, occupying the outer layer of the double-layered duct epithelium of the pancreas. The endocrine cells showed no evidence of reaching the duct lumen, i.e., they are closed in type.
By the use of immunohistochemical techniques, insulin-, glucagon-, somatostatin- and pancreatic polypeptide (PP)-like immunoreactivities were detected in the endocrine cells. The PP-positive cells could not be differentiated from the somatostatin-immunoreactive cells, although the former were smaller in number. The possible reasons for this result were discussed.
The present finding supports the view that those four peptides are essential regulatory substances of the endocrine system of the pancreas at a fairy early stage of vertebrate evolution.

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