In 229 dd-mice of both sexes ranging in age from birth to 300 days, the occurrence of lymphoid tissue in the pineal region was examined histologically and histometrically.
In adult mice, the lymphoid tissue appeared usually as small nodular accumulations of small lymphocytes posterior to the pineal stalk. It was commonly localized in close relation to the venous vessels which, arising from a vein from the midbrain, run upwards along the posterior border of the pineal. In addition to lymphocytes, the lymphoid tissue contained varying numbers of plasma cells which tended to increase in number with age.
The lymphoid tissue was not found in mice younger than 10 days. At 15 days it first occurred as a small patch of small lymphocytes in 11% of the cases examined. Thereafter, the lymphoid tissue increased in size and amount rapidly with advancing age. After 60 days the lymphoid tissue commonly appeared as a nodular accumulation of lymphocytes. In each age group after 60 days the lymphoid tissue was found in more than 90% of the cases examined. The nodular lymphoid tissues measuring 50 to 150μ in diameter were most frequent, but the larger ones tended to increase in number as age increased. The lymphoid tissue tended to increase in total amount with advancing age.

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Surface ultrastructure of the bovine rumen mucosa was observed by the scanning electron microscope. The luminal surface was divided by the primary and secondary grooves, which run more regularly in the anterior pillar than in the rumen papillae. The boundaries of the horny cells in the stratum corneum were indicated by narrow lines of cell membrane devoid of any projections. Numerous granular or fold-like projections were noted on the cell surface which apparently originated from the thickened cell membrane of keratinizing horny cells. The type and density of these projections varied from cell to cell. As for the surface ultrastructure, no prominent difference was found after four different fixations. Colonies of a ruminal bacteria, probably of diplococcus type, were noted on the horny cell surface. The presence of the numerous projections provided extensive surface area to the rumen mucosa. This suggested that they are an important part of the absorptive apparatus in the rumen mucosa.

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The thyroid glands of eight rabbits, fifteen cats and eight mice of various ages and both sexes were made into serial sections, one lobe from each individual, and investigated by means of silver impregnation, pseudoisocyanin and lead-hematoxylin stainings. It was recognized that the parafollicular cells stained by these techniques were not restricted to the thyroid gland but were also distributed in the parathyroid IV and thymus IV.
1. In rabbits the parafollicular cells occurred in the parathyroid IV in six out of seven cases. Although the proportion of parafollicular cells to parathyroid cells differed from individual to individual, it reached 10% in the most numerous case.
2. In cats the parafollicular cells constantly occurred in the parathyroid IV. They were found also in the thymus IV of nine out of eleven cases. From forty to fifty parafollicular cells were generally counted in cat parathyroid IV. In two cases with numerous parafollicular cells, they were estimated as 1-3% of the parathyroid cells. In the thymus tissue their population was lower than in the parathyroid gland.
3. No parafollicular cells were found in the parathyroid III and the thymus III.
4. The distribution of parafollicular cells in the thyroid of rabbits and mice was confined in a more or less restricted region of the gland around the parathyroid IV and thymus IV, or around ciliated cysts (vide infra).
5. In all three species a few ciliated cysts containing a foamy colloid-like substance constantly occurred in the thyroid grand.
6. These observations were discussed in relation to the ultimobranchial origin of the parafollicular cells.

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The intercellular bridges between the spermatogonia in adult man were observed by electron microscopy with the following results.
The bridges were usually barrel-shaped with a slight convexity at the middle (1.0-1.5μ both in diameter and length). A layer of an electron dense material (40-50mμ thick) occurred directly beneath the plasma membrane of the bridges. Besides various cytoplasmic organelles, microtubules were frequently found in the bridges.
The bridges were demonstrated between type A as well as type B spermatogonia. It was proposed that the synchronizing differentiation, by means of the intercellular bridges, of the germ cells starts from the division of “dark type A” spermatogonia into “pale type A” spermatogonia (designation by CLERMONT), and that thereby it is possible to yield groups of, at the most, thirty-two interconnected spermatids. The concept of FAWCETT (1961) that the intercellular bridge first occurs between primary spermatocytes as result of the last spermatogonial division and that the groups of eight interconnected spermatids are subsequently formed was criticized.

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Carotid bodies of amphibia (Cynops pyrrhogaster pyrrhogaster, Rana nigromaculata, Rana catesbeiana, Bufo bufo japonicus), a lizard (Eumeces latiscutatus), birds (Uroloncha domestica, Gallus domesticus) and mammals (rat, mouse, dog) including three human fetuses (6, 7 and 9 months) were studied with reference to the occurrence of monoamine-storing cells. The methods used were light microscopic chromaffin reaction after fixation in dichromate containing fluids and Falck and Hillarp's fluorescence histochemical technique.
In the amphibia, dog and human fetus, some parenchymal cells showed a positive chromaffin reaction, while in the lizard, birds, rat and mouse no chromaffin cell was recognized at all. This finding confirmed the previous descriptions of the irregular occurrence of chromaffin cells in the carotid bodies in various vertebrates.
In fluorescence microscopy of freeze-dried and formaldehyde-treated specimens, the cytoplasm of all the chief cells of the avian and mammalian carotid bodies showed green or yellow-green fluorescence. In the lizard, fluorescent cells were found singly or in small groups in the adventitia of the carotid arch where the internal carotid artery arises. In the amphibian carotid bodies cells with intense yellow fluorescence occurred within the interstitial tissue of the capillary plexus. These findings indicated the presence of monoamine-storing cells in the carotid bodies of all vertebrate species examined.
It was concluded that the absence of chromaffin reaction in the carotid body did not always mean the non-existence of monoamines in the cells, but it may imply the presence of small amounts of them. The carotid body could not be classified into non-chromaffin paraganglion on the basis of its chromaffin reaction.
Possible functional role and possible mode of the presence of monoamines in the carotid body were briefly discussed.

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Outer segments of frog visual cells were, after aldehyde fixation, treated with chloroform-methanol for the elimination of the lipid composition of the membranes. The outer segment contour was well preserved after the treatment, but the osmium stainability of both rod and cone decreased as compared with the control specimens.
In the treated cone outer segment, disc membranes were disintegrated only to a small extent and 61Å globules were recognized. The globular substructure in the discs of control specimens was 67Å in diameter. In the rod the discs had mostly disappeared leaving only the disc edges after the treatment. Globules in the rod outer segment 47Å in diameter as contrasted to 69Å in the control discs.

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Intranuclear tubular bodies are described in the pancreatic A and B cells of apparently healthy normal rabbits, rats, hedgehogs and pigs. The bodies consist of a central bundle of parallel tubules and a peripheral muff.
The intranuclear tubular bodies are considered to be normal structures in the cell nuclei.

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