Formation of neuromuscular junctions in embryonic cultures has been reviewed. Anatomical and electrophysiological evidence has been presented which demonstrates the formation de novo of synaptic contacts between nerve and muscle in culture; in (1) organ cultures of spinal cord explanted intact with attached myotomes, (2) organ cultures of in vitro coupled explants of spinal cord and skeletal muscle fragments, and (3) monolayer cultures of dissociated myoblasts confronted either with spinal cord fragments or cells. Innervation across species lines has also been demonstrated in explants of spinal cord and skeletal muscle from different species These cultures should provide a useful system for analysis of the mechanisms underlying the trophic and other interactions during neuromuscular development.

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The occurrence, distribution and forms of the parafollicular cells in the thyroid and some neighboring branchiogenic organs were examined in serial sections of the thyroid of 34 dogs. For the identification of the parafollicular cells, silver impregnation, pseudoisocyanin and lead-hematoxylin stainings were employed.
1. Besides the ordinary parafollicular cell groups in the thyroid, a few parafollicular cell complexes of hitherto unknown structure were found within and adjacent to the gland. In experimentally induced hypercalcemia the parafollicular cells in the cell complex underwent degranulation and showed an increased mitotic activity as the ordinary parafollicular cells did.
2. The main type of parafollicular cell complex consisted of very numerous parafollicular cells, a few columnar epithelium cell masses and cysts lined by single columnar epithelium which was for the most part non-ciliated. They were generally oval in form and usually separated from the thyroid parenchyme by connective tissue. The largest complex was 2.5mm in long diameter.
3. Another type of parafollicular cell complexes contained small polygonal cells and microfollicles in addition to the above mentioned constituent elements. This type of complex was fused with the thyroid parenchyme and generally exceeded the former type in size, often measuring 3mm in long diameter.
4. The parafollicular cell complexes were frequently found around the parathyroid IV adjacent to or included within the thyroid gland. Sometimes did they build up a complex with the parathyroid IV or thymus IV. Twenty-four of thirty-four thyroid lobes cut in serial sections, one lobe from each individual, possessed a parafollicular cell complex or complexes.
5. Dispersed parafollicular cells sometimes were found within the parathyroid IV and thymus IV.
6. The ordinary parafollicular cells were diffusely distributed throughout the whole thyroid gland. A precise examination of serial sections indicated, however, that they tended to be more common around the parathyroid IV.

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The brain of rats in which hypertensive encephalopathy was induced by means of constriction of the main renal artery was examined under the electron microscope.
The most remarkable changes in the brain were swelling of perivascular astrocytes and an enlargement of the extracellular spaces. The latter was confined only to the white matter. These findings were compatible with those of the “vasogenic type” of brain edema as described by KLATZO.
A remarkable increase in the number of pinocytotic vesicles and caveolae intracellulares was noticed in the endothelial cells of capillaries and venules. Marginal vacuoles were frequently encountered in the endothelium. Tight junctions between the endothelial cells of capillaries and venules appeared intact. The present study suggested that the vesicular transport in the capillaries and venules plays an important role in conveying edema fluid through capillary walls to brain tissues. The increased pinocytotic activity was thus conceived to represent one factor causing brain edema at least in hypertensive encephalopathy.

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Mitosis of the rat anterior pituitary cells was studied with the electron microscope. Most mitotic cells found in the anterior pituitary contained a number of secretory granules, and a somatotrophic cell in metaphase contained a Golgi apparatus with newly formed secretory granules. Hypertrophied thyrotrophic cells after thyroidectomy underwent mitosis. Some prolactin-producing cells in mitosis contained a great number of vacuolated cisterns of rough endoplasmic reticulum, which were the characteristic results of long term administration of estrogen to female rats. Hypertrophy of the anterior pituitary glands after removal of a target organ or the administration of estrogen may be brought about by the proliferation of cells of a specific type corresponding to the experiment. This proliferation carried out by mitotic cell division of fully differentiated adenohypophyseal cells. The theory that highly differentiated cells producing specific hormone cannot synthesize DNA and divide by mitosis was shown to be erroneous.
The outer layer of a kinetochore was bent by the pulling force of chromosomal spindle tubules. As the inner layer was not bent in this case, it became clear that the spindle tubules do not penetrate through the kinetochore, and the contraction of chromosomal tubules is believed to exert the force for the initial movement of anaphase chromosomes.

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Renal glomeruli of rats, from neonatal to 10 days old, were studied by scanning and transmission electron microscopy with special reference to the morphological differentiation of podocytes.
1. Transmission electron microscopy of sections indicates that the columnar cell of the visceral epithelium of the Bowman space begins to differentiate into podocyte by issuing from its base finger-like processes which are inserted into the base of its adjacent cells. The first interdigitations of the podocyte processes are formed by an exchange of these basal processes between the closely standing columnar cells. The initial narrow arcades in the cell base to contain the inserted processes, meanwhile, are largely excavated so that the foot processes across a cell or cells have chances to meet here.
2. After the cells begin to be separated from each other, scanning electron microscopy reveals how the foot processes develop in size and shape to cover the growing surface of the blood capillary. Thicker cytoplasmic processes are formed secondarily to combine the end feet and the cell body which may become quite separated from its original position.
3. It was concluded that, throughout the differentiation of the podocyte, foot processes derived only from different cells are adjacent with each other, and the concept of SUZUKI (1959) and BUSS (1970) that the foot processes produced within a single cell by basal incisures become interdigitated by the complication of the latter was criticized.

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