Afferent lymphatic vessels to the popliteal lymph node in the rat were blocked, and the node was histologically examined 2-35 weeks later. After the operation, the node was reduced in size and its lymphoid structures, such as germinal centers, lymph follicles and deep cortex units, were decreased in size and number. At 16 weeks, the lymphoid organization of the node reached a minimal level, but the node still exhibited reduced numbers of lymphoid structures. The lymphoid parenchyma of the node, although reduced in size, showed no noticeable change in cellular density during the period of observation. The changes observed in the popliteal node following blockage of the afferent lymphatics were interpreted as resulting from a reduced supply via the afferent lymph of antigens and other factors on which the development and persistence of the lymph node structures are believed to depend.

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The upper molars of adult Wistar rats were moved lingually by a wire spring for 5 and 9 days. Collagen-containing fibroblasts in the pressure zone caused by the tooth movement were investigated morphologically (forms characterized by type A and type B compartments) and cytochemically (location of acid and alkaline phosphatase activity). The following results were obtained: 1) The distribution of collagen-containing fibroblasts with type A or type B compartments could not be distinguished clearly in either 5-day or 9-day specimens; 2) Acid phosphatase activity was recognized in the Golgi apparatus, lysosomes, and elliptical bodies associated with type B compartments; 3) Alkaline phosphatase activity was positive in the plasma membrane of collagen-containing profiles and in both intracellular and extracellular collagen fibrils.
These results suggest that fibroblasts are capable of phagocytosing collagen fibrils in all areas of the cytoplasmic membrane and that digestion of collagen fibrils in fibroblasts may be associated with acid and alkaline phosphatase.

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Substance P and 5-hydroxytryptamine containing presynaptic boutons on presumed α-motoneurons were studied in the chicken ventral horn using the indirect antibody peroxidase-antiperoxidase technique in conjunction with monoclonal antibodies to 5-hydroxytryptamine and substance P both at light and electron microscopic levels. At the light microscopic level, substance P immunoreactivity was observed as large dot-like structures in close apposition to the soma and dendrites of presumed α-motoneurons. Individual immunoreactive structures were separated from each other. On the other hand, 5-hydroxytryptamine immunoreactivity was observed as many small dot- or fiber-like structures outlining the soma and dendrites of large neurons in the ventral horn. Electron microscopically, 5-hydroxytryptamine immunoreactive presynaptic boutons were identified as the type which contained elongated dense cored vesicles concomitant with flattened clear vesicles, while the substance P immunoreactivity was observed in presynaptic boutons which contained spherical dense cored vesicles (diameter range 60-110nm) together with spherical clear vesicles. Both types of dense cored vesicles were often adjacent to the presynaptic membrane of synaptic specialization. These immunocytochemical results suggest that α-motoneurons may be directly modulated by substance P and 5-hydroxytryptamine in the chicken.

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Arachnid granulations are not always present in lower mammals and primate newborns. In order to visualize the route for the cerebrospinal fluid (CSF) to drain into the venous system, horseradish peroxidase (HRP) was injected into the lateral ventricle or cisterna cerebellomedullaris of the mouse and rat.
From 30 to 60min after the commencing of a slow infusion for 15-30min of 0.05-0.1ml solution containing 10-20mg HRP, the mouse, whose skull had been exposed, was dropped into cold acetone at dry ice temperature; other animals were fixed by perfusion with aldehyde solution. The frozen head was dissected in a cryostat kept at -18°C to remove the skull, but leave the dura mater and the falx cerebri. The brain with meninges was cut into 30-45μm sagittal sections in the cryostat, and processed for peroxidase reaction. The perfusion-fixed brains were used for scanning electron microscopy and for electron microscope observation of the tracer.
The reaction product was found within fenestrated venous capillaries of the choroid plexus. The route for the HRP in the CSF to drain into the sinus rectus via the vena chorioidea and vena cerebri magna was directly visualized in the mouse.

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Both the development of red pulp and hemopoietic activity in spleen obtained from 62 human embryos and fetuses between 30 days and 20 weeks after ovulation were investigated light and electron microscopically.
The spleen develops in the left-posterior portion of the dorsal mesogastrium at 35-40 days after ovulation. At the 8th week after ovulation, reticular cells formed a threedimensional meshwork. Two types of reticular cells (dark and clear reticular cells) were observed in the splenic cord in the 12-13th week after ovulation.
Mature hemopoietic cells, mostly of the erythroblastic series, increased in number in the extravascular spaces with the development of the fetus. However, presumptive hemopoietic stem cells or “undifferentiated mononuclear cells” (FUKUDA, 1973a) did not appear in the spleen. Moreover, immature hemopoietic cells such as proerythroblasts, myeloblasts and megakaryoblasts could not be detected. Therefore, despite the occurrence of a welldeveloped reticular cell network, hemopoiesis was judged to have not taken place in human fetal spleen.
Macrophages appeared in the spleen at the 8th week after ovulation and increased in number with the the development of the fetus. Phagocytosis of decrepit blood cells proved to be an essential function of the spleen.

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The fine structure of interrenal cells in the salamander, Hynobius nebulosus, from prometamorphic larvae to its adult stage, was observed with electron and light microscopes. In all the animals examined the interrenal cell clusters were located at the medial edge of the ventral surface along the total length of each kidney, suggestive of a primitive nature.
In larval salamanders, the interrenal cells contained small to moderate numbers of lipid droplets, and their cytoplasm was filled with a tubular network of smooth endoplasmic reticulum (SER) and numerous mitochondria with tubulo-vesicular cristae. In the adult and young adult salamanders, however, most interrenal cells were filled with lipid droplets, so that both tubular SER and mitochondria were decreased in amount in inverse proportion to the increased lipid droplets. These mitochondria frequently contained a crystalloid structure composed of closely packed tubules which were continuous with the cristae. These findings suggest that the interrenal cells in the larvae are more active than those in the adult or young adult salamanders. In addition, the interrenal cells at the end of metamorphosis contained a greater number of enlarged mitochondria with loosely distributed tubular cristae and with a less dense matrix and more numerous membrane-bounded dense bodies, 0.1-0.3μm in diameter, than those at the prometamorphic stage. These findings suggest that the cells are their most active at this stage. In the prometamorphic larvae, bundles of filaments frequently occurred in the cytoplasm, especially around the nucleus. These filaments gradu ally decreased in number with the advance of age, and in young adult salamanders they appeared only occasionally.

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The nerve endings in the subepithelial tissue of the surgically removed human epiglottis were observed by electron microscopy. The nerve varicosities (3-6μm in diameter) with an accumulation of mitochondria and interconnecting nerve fibers supported by Schwann cells constituted the glomerular corpuscles (50-70μm in diameter). The processes of the nerve varicosities, containing small clear and large dense cored synaptic-like vesicles, were in contact with basal cells of the stratified squamous epithelium. The glomerular corpuscular nerve endings are presumed to be concerned with low threshold mechanoreceptive functions, such as tactile sensation.

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Epithelial-mesenchymal interfaces in the stomodeal side of the rat mandibular processes were observed at Theiler's stages 14 and 15, when no epithelial organogenesis could be detected by electron microscopy.
At stage 14, the basal lamina was discontinuous. Disintegrated basal lamina-like materials were seen in the epithelial-mesenchymal interface. A number of coated vesicles and smooth vesicles were seen in epithelial cell processes adjacent to the disintegrated basal lamina-like materials. Some epithelial cell processes penetrated into the mesenchymal space through the basal lamina and touched the ectomesenchymal cells. Other epithelial cell processes or satellite cell bodies protruded into the mesenchymal space, but were covered with basal laminae.
At stage 15, the basal lamina was smooth and continuous with partial duplications.
Ruthenium red-positive anionic sites were distributed in the basal lamina and on thin filaments underneath the basal lamina. At stage 15, the separation among anionic sites became more regular than that at stage 14.
In this study we found some stage-specific morphological events in the epithelialmesenchymal interface in the stomodeal side of the mandibular process at stages preceding the initiation of epithelial organogenesis.

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Laser irradiation-caused features of neuronal regrowth containing enkephalin-like immunoreactivity in the myenteric plexus around the necrosis were investigated in the guinea pig jejunum and proximal colon using an antiserum to methionine-enkephalin-Arg⁶-Gly⁷-Leu⁸. The power level and irradiation time of the argon laser beam were adjusted to make a coagulation spot of about 0.5mm in diameter.
A distinct accumulation of the immunoreactivity occurred in the laser photocoagulated ends of the enkephalin neuron processes. Regeneration of the severed axon-like process took place in the following order: 1) swelling and budding at the severed proximal end; 2) elongation and branching of newly-formed nerve fibers; and 3) formation of a tangled overgrowth. Approximately 43-90hrs after the laser microsurgery, immunoreaction of the enkephalin neuron perikarya was stronger in the first several rows of ganglia, on both the oral and anal sides of the laser necrosis. In the jejunum, an increase in the intensity of the immunoreaction was more prominent on the oral side than on the anal side, whereas the proximal colon displayed an opposite state. In the jejunum, the anally-directed axon-like process of the enkephalin neurons transported a larger amount of the immunoreactivity as compared with the orally-directed wing-ramuli.
This paper seeks to prove that the laser irradiation combined with immunocytochemistry may provide a simple and reliable methodology for the study of the projections of enteric neurons.

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