The dome area of Peyer's patches in adult mice was studied by electron microscopy. The cellular constituents of the area are lymphocytes, plasma cells, macrophages and reticular cells. Macrophages are filled with numerous lysosomal bodies containing dead lymphocytes or plasma cells. The epithelium covering the dome is infiltrated with numerous lymphocytes, a few plasma cells and macrophages. These wandering cells first are found intercellularly but later appear to penetrate into the epithelial cell cytoplasm just beneath the cell apex. The epithelial cells containing the wandering cells in the supranuclear portion protrude into the intestinal lumen, and their microvilli are short and scanty. The epithelial cells covering the dome often have inclusion bodies containing dead wandering cells. Such modification of the epithelial cells may be related to the presence of underlying follicles.
The results suggest that the dome including the covering epithelium is a site in which antigens from the intestinal lumen might come in direct contact with lymphocytes or other wandering cells.

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Hemostatic reaction in the mural thrombus formation (up to 2hrs) was examined by scanning electron microscopy after removal of the endothelium in the rabbit carotid artery by the use of a rough-surfaced needle.
The endothelium was almost completely removed leaving a network of subendothelial microfilaments which sometimes appeared half embedded in the basement membrane. Platelet adhesion occurred on this subendothelial tissue in the following steps: attachment of discoid platelets, pseudopod formation and spreading. The subendothelium was thus covered by a layer of platelets in about 10min. During adhesion they caught the microfilaments by their pseudopods and never produced hemispherical protrusions. Loose aggregates of the rounded platelets were then formed on them but they were frequently reversible, resulting in 1-2hrs, in coverage by only one or two layers of the adhered platelets. This platelet reaction was weaker than that to collagen in case of bleeding in the previous report. Leukocyte participation in thrombus formation began at around 30min.
Fibrin strands appeared as tiny filaments which were attached exclusively to the activated platelets and later grew into thick and long fibers forming a network. Thus activated platelets seemed to be very important as the base of development of fibrin thrombus.
Many erythrocytes were demonstrated to be destroyed at the mural thrombus after attaching to either the subendothelial components or activated platelets or fibrin strands and being deformed by the blood stream. This finding supports the hypothesis of microhemolysis in the hemostatic process by HELLEM (1961).
This type of hemostatic reaction was proved to be caused by a slight manipulatory pressure on the arterial wall, suggesting the occurrence of thrombus formation in our daily life.

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Ciliogenesis in the epithelium of the oviduct ampulla of 5-9 day-old mice has been investigated by electron microscopy.
As reported by many investigators, fibrous granules, deuterosomes, and procentrioles are important for ciliogenesis. After injection of colchicine, fibrous granules desappear, while numerous coated vesicles and lysosome-like dense bodies appear in the same region, and the formation of deuterosomes and procentrioles is impeded.
In the ciliogenic cell, the Golgi apparatus, consisting of numerous vesicles, is very well developed, and a large number of microtubules are distributed between the supranuclear and apical cytoplasm. In addition to these, many small vesicles, some of which are fused with the plasma membrane, occur in the apical cytoplasm. These vesicles, which may be derived from the Golgi apparatus, are considered to be necessary for the apical plasma membrane, because the protrusion of cilia requires additional plasma-membrane substance during their differentiation and development. The microtubules, some of which are connected with these vesicles, might play some role in the movement of these vesicles from the Golgi field to the apical cytoplasm.
When colchicine is administered to suckling mice, formation of microtubules is blocked in the upper part of the ciliated cell, and the apical vesicles disappear. This also indicates that the microtubules bring the vesicles from the Golgi field to the apical region of the cell.

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The fine structure of the sarcoplasmic reticulum (SR) in the smooth muscle of Mytilus and the localizaion of intracellular calcium at rest and during acetylcholine-induced contraction were studied using the pyroantimonate-osmium (PAO) technique.
1. The SR showed vesicular and tubular elements which were alternately interconnected along the axis of the fiber. Transverse components were sometimes observed. The vesicular elements of the SR formed specialized junctions (couplings) with the plasma membrane.
2. The electron opaque precipitate which formed in the SR, mitochondria and on the inner surface of the plasma membrane after treatment with PAO was proven to be mainly Ca-pyroantimonate by both energy-dispersive and wavelength-dispersive X-ray microanalysis.
3. In muscle fibers treated with PAO shortly after the peak of contraction, the SR was the last site of the three Ca-accumulating sites in which the precipitate was relocalized. This finding suggests that the SR plays a principal role in the regulation of the contraction and relaxation cycle.
4. Fused paramyosin filaments were not observed during the catch state.

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The prenatal development of cheek-teeth of rabbits was studied by histological methods. Females from 15 to 30 days of gestation were sacrificed and their fetuses were collected and decapitated. The heads were fixed in buffered neutral formalin and paraffin embedded. Sagittal and frontal sections of 7μ were obtained and stained with hematoxylin-eosin. The first tooth-germs observed were the m³ and m₃, in the animal of 16 days of fetal life. One day after the m⁴ and m₄ are observed in the bud stage. The last teeth to initiate development in the fetal rabbits are the M³ and M₃ at 30 days. Only the m³, m⁴, m₃ and m₄ start cementogenesis in the prenatal stage.

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Organs of fish, amphibian, reptile, bird and mammals when stained by Sirius Red and studied with polarization microscopy present different colors in regions where collagens I, II and III have been described.
Collagen type I presented a yellow, orange or red color while collagen type III appeared green. Collagen type II, present in cartilage and chondrosarcoma showed a variable color according to the tissue and the species. Its color and morphology however always permitted its clear distinction from collagens type I and type III.

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The seminal vesicle of the adult Japanese monkey was observed by scanning electron microscopy. A number of spermatozoa are found scattered on the luminal surface. Some of them are normal in appearance, while others disintegrated. The epithelial cells bulging slightly into the lumen are devoid of cilia, but provided with diffusely distributed microvilli. The fracture surface reveals that the epithelium of the seminal vesicle consists of columnar epithelial cells with secretory activity and occasional basal cells, in accordance with the finding obtained by transmission electron microscope in other mammals.
The most striking observation of this study is the occurrence of a number of macrophages lying on the epithelium of the seminal vesicle. They also are seen to engulf the disintegrated spermatozoa in bulk. The intraluminal macrophages observed may serve to dispose of spermatozoa which have migrated into the seminal vesicle for some unknown reason.

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Radioactivity in adrenal medullary chromaffin cells of the mouse was examined by autoradiographic methods 15min to 1hr after an intraperitoneal injection of ³H-dopa. In the normal control mice, the concentration of radioactivity was significantly higher in the A cells than in the NA cells, whereas in the hypophysectomized mice (9 days after operation by the transauricular method) the radioactivity was evenly distributed in the two cell types. It was suggested that both A and NA cells possessed a special trapping and concentrating mechanism for extracellular dopa and/or its metabolites and that the activity of this mechanism was made greater in the A cells than in the NA cells by the pituitary gland.

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