Electron microscope observations demonstrated bundles of microfilaments measuring 40-70Å in diameter in the granulosa cells of normal developing follicles of rabbit ovary.
The microfilaments appeared concentrated in the cortical areas of the cytoplasm and within large evaginations and microvilli. In addition the filaments were particularly abundant in the granulosa cells of corona radiata and free cells in the cavity.
Immunofluorescent staining on frozen sections of rabbit ovary demonstrated that the granulosa cells of developing follicles bind antimyosin-like antibodies (AMA). Considering the correspondence between the immunochemical and ultrastructural findings it is suggested that the microfilaments contain a “myosin-like” protein.
It seems then reasonable to suggest that the ovarian follicles are not kinetically passive organs, but they contain contractile filaments for their specific functions.

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The development of the submandibular gland of the rat was studied between days 2 and 55 of the postpartum. Besides confirming previous ultrastructural findings we observed at the electron microscope that the architecturally complex terminal tubules, proacinar, acinar and striated duct cells retained during mitosis the major ultrastructural features they exhibited in interphase. The ultrastructure of cells that were in the S period of the proliferative cycle was evaluated in high resolution autoradiographs from rats injected with thymidine-H³. All cell types were thus studied and no obvious cytoarchitectural modifications could be detected in these cells preparing for division. We obtained ultrastructural evidence that between days 20 and 30 some terminal tubule cells undergo transformation into acinar cells.
The intercalated duct cells showed the highest rate of proliferation and the lowest daily increment in number. This suggests that cells from the intercalated ducts migrate to the neighboring morphological compartments. Quantitative data on the rate of cell proliferation and accumulation in the striated duct indicated that cells from the intercalated ducts should differentiate into striated duct cells. Differentiation of intercalated duct cells into the terminal tubule cells was observed with the electron microscope.

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An electron microscope study was made on the tooth germs of Hoplognathus fasciatus in early developmental stage. Special attention was given to the odontoblasts, enameloid matrix fibers, calcification of enameloid and the hitherto controversial origin of the enameloid.
1. The ameloblasts and the odontoblasts are demarcated by a single layer of basement membrane which persists until immediately before the calcification of the enameloid matrix.
2. The histogenesis of the enameloid matrix begins with the formation of non-striated fibers 140-180Å thick. They are arranged in a direction vertical to the basement membrane and parallel to the sides of odontoblasts. Fibers with regular cross striations of 640Å periodicity later appear and the entire enameloid matrix is formed by these fibers.
3. Along with the formation of the enameloid, the odontoblasts assume a high columnar form, with a marked increase in cell organelles which show marked polarity suggesting active protein synthesis. Numerous odontoblastic processes are noted in the enameloid matrix. Granules, representing precursors of enameloid matrix fibers occur in the odontoblasts. Based on these findings, the enameloid matrix fibers must be of mesodermal origin.
4. Deposition of crystals of small size, needle and tube in shape, occurs in the circumference of the fiber bundles. As calcification progresses, crystals appear in the central portion of the bundles. Later, large crystals of rod and platelet shapes become intermingled. In addition to this, small crystals are fused, forming aggregates.

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Tissue pieces were made conductive by osmium impregnation (revised tannin-osmium method of MURAKAMI, 1974) and embedded in hydroxy ethyl methacrylate. The resin-embedded specimens were cracked and observed, with neither elimination of resin nor metal coating, in the scanning electron microscope. Using the bone marrow of the rat femur, it was shown that this resin-embedding preserved the delicate tissue-elements without undesirable dislocation and breakage and assured the effective scanning observation as high as ×10, 000 at 25kV accelerating voltage. Passage of blood cells through the sinus wall was thus clearly demonstrated.

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Endocrine cells in the normal glandular stomach and gastric carcinoids of mastomys were observed by electron microscopy and at least five types of endocrine cells, EC, G, D-like, R (round-granule) and ECL cells were identified. Of these, four types excepting G cells were recognized in the fundic mucosa. Characteristic in mastomys was a scarcity of endocrine cells in the fundic mucosa, where ECL and R cells were predominant types.
Silver impregnation methods including SEVIER-MUNGER's argyrophil reaction of our own modifications were applied to tissue sections and the endocrine cells were examined by electron microscopy. Only EC cells revealed argentaffin granules under the light and electron microscope. R, ECL and some of the G cells were non-argentaffin and argyrophil in reaction and D-like cells and the rest of the G cells failed to show even an argyrophil reaction. Granules of mastomys carcinoid cells, as noted in the previous reports, were non-argentaffin but faintly argyrophil.
Mastomys gastric carcinoids were studied by the same method, with special reference to the parant cells of this particular neoplasia. Noteworthily, mastomys gastric carcinoids arise mostly from the fundus, the area where R and ECL cells mainly occur in normal animals. The neoplasms are composed of cells containing granules resembling partly those of R cells and partly those of ECL cells. ECL cells and neoplastic cells in the present investigation have a similar reactivity to SEVIER-MUNGER's method.
Considering the generally accepted fact that neoplastic cells may not fully duplicate their parent cells in cytological features, it seems reasonable to presume that R and/or ECL cells might be the parent cells of the mastomys gastric carcinoids. In connection with this assumption histamine has been demonstrated to be produced both in mastomys carcinoid cells and normal ECL cells.

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