Terminal Bars Research Articles

Access of horseradish peroxidase (HRP) to the extracellular spaces of the maturation zone of the rat incisor enamel organ

Adult rats received a single dose of HRP intravenously and were killed from 10 min to 6 hr after injection. Following fixation with glutaraldehyde, the enamel organs were treated with a Graham-Karnovsky-type procedure for peroxidase activity, post-osmicated, and embedded in plastic. Sections were studied with light and electron microscopes. Ten minutes after injection, reaction product was found in all extra-cellular spaces of the enamel organ, at the enamel-ameloblast interface over smooth-ended and intermediate ameloblasts, and in apical surface invaginations and vesicles of the latter cell types. The enamel-ameloblast interface over the ruffle-ended aemlo-blasts and the extracellular spaces within the ruffled border were free of reaction product and remained so for up to 6 hr. The apical terminal bars of the ruffle-ended ameloblasts functioned as a barrier to HRP. The basal terminal bars of the smooth-ended ameloblasts likewise seemed to prevent the passage of the HRP. Possibly, HRP flows in a lateral direction from groups of ruffle-ended into groups of smooth-ended ameloblasts. Between 10 min and 6 hr, HRP was cleared more rapidly from the extra-cellular spaces of the papillary layer than from those of the ameloblast layer, and there was little backflow of tracer from the ameloblast into the papillary layer. Eventually, tracer was cleared also from the extracellular spaces of the ameloblast layer, probably mainly through micropinocytosis by the ameloblasts. A working model is proposed regarding the handling of large molecules by the enamel organ in the maturation zone.

Migration and turnover of entero-endocrine and caveolated cells in the epithelium of the descending colon, as shown by radioautography after continuous infusion of 3H-thymidine into mice.

Adult male mice were given a continuous infusion of about 0.5 muCi of 3H-thymidine per gram body weight per day for periods varying from 1 to 60 days. Semithin sections of descending colon were cut from/plastic-embedded blocks and stained by a method combining silver impregnation and iron hematoxylin, by which argentaffin entero-endocrine cells and caveolated cells could be identified. From radioautographs, the labeling index of these cells was determined. One to three days after the beginning of 3H-thymidine infusion, label is observed in some of the stained entero-endocrine cells in the bottom of the crypts; the apices of these cells reach the crypt lumen and are joined to neighboring cells by terminal bars (junctional complexes). After five to seven days, labeled entero-endocrine cells are seen on the sides of the crypts, where their base stretches along the basement membrane and their apex has lost its terminal bar connections to neighboring cells. Finally, by 13 and 24 days, labeled cells are observed within the epithelium at the mucosal surface. The turnover time, which is taken to be equal to the mean time required for migration from site of origin to site of loss on the mucosal surface, has been estimated at 23.3 days. This is much longer than the 4.6 days required by the two main cell types of the epithelium -- vacuolated-columnar and mucous cells -- to travel the same route. It is likely that, after entero-endocrine cells lose their terminal bar attachment to other epithelial cells, they migrate independently and very slowly. Labeled caveolated cells are first seen in the crypt bottom one day after the beginning of 3H-thymidine infusion. By three to five days, they are on the sides of the crypts; their base is stretched along the basement membrane, but their apex retains its attachment to neighboring cells by terminal bars. By seven days, labeled caveolated cells are on the mucosal surface. Their turnover time has been assessed at 8.2 days. This is, again, longer than for the two main types to which they are bound by terminal bars throughout migration. The discrepancy is explained by the caveolated cells arising deeper in the crypts than most vacuolated-columnar and mucous cells.

Prinzipien des epithelialen Transportes in Niere und Darm

Epithelia of kidney and small intestine consist of one layer of cells which, at their luminal edge, are linked together by terminal bars. Solute transport proceeds either across the cells, which is true of all active transports, or it proceeds paracellularly through the basolateral spaces and terminal bars and is then passive. The driving force for the active transport of a substance is derived either directly from metabolism (primary active transport), or from the gradient of another solute, usually Na+, which in turn is created by primary active transport. In the latter case the transport is referred to as secondary active. The driving forces of passive transport are the electrochemical gradient of the respective substance and solvent drag. The proximal parts of the kidney as well as of the intestine are leaky so that a considerable part of net reabsorption proceeds passively. Their distal parts, however, where the transport is regulated, are tight so that large concentration differences can be created and maintained. Transcellular active transport is only possible if the cells are polar, i.e., the transport characteristics of the luminal cell membrane differ from those of the contraluminal cell membrane. By measuring the cellular electrical potential difference or by measuring transport into isolated plasma membrane vesicles from either cell side the driving forces for the two transport steps, the luminal and contraluminal, have been elucidated. Schemes for the transport steps in the proximal tubule and in the small intestine are given. They show the principal similarity of the transport of many substances in both epithelia.

The allantoic and amniotic epithelia of the pig: SEM and TEM studies

The epithelial layers of the allantoamnion of pig embryos and fetuses during various gestational ages were studied utilizing SEM, TEM, and light microscopic histochemistry. The allantoic endoderm exhibits a gland-like secretory activity and thereby differs greatly from that of other mammals. On the surface of this unilaminar cuboidal epithelium, the majority of the cells exhibit characteristic short vermiform ridges, while some protruding cells display larger individual microvilli. These two cell types are also distinct in thin sections. The more common “granular cells” with short and blunt microvillous projections and a lobated nucleus are characterized by small, Golgi-derived secretory granules in the apical cytoplasm showing a positive PAS-reaction. They contain vast glycogen deposits. Extensive regions of lateral interdigitations are found. In the younger stages, membrane thickenings of the apical plasmalemma resemble those of the urinary bladder. The cytoplasm harbors many more interwoven filaments than organelles. The second cell type, the “mitochondria-rich cells”, bearing longer apical microvilli in many cases, only constitutes up to 3% of the mucosal cell population. They are frequently flask-shaped, heavily reactive to oxidoreductases, and rich in lysosomes but have smaller glycogen deposits. Mitochondria-rich cells lack secretory granules but have light apical tubules, probably of endocytotic character. These cells can be found in different functional states. The amniotic epithelium is simple squamous in the younger stages and largely resembles that in other mammals exhibiting cells with few organelles but rich in filaments. Each terminal bar consists of a zonula occludens only which may open toward the end of gestation. In older fetuses, small stratified areas of cells sloughing off into the lumen appear as blisters which contain large vacuolated cells.

Junctional complexes and variations in gap junctions between spinal cord ependymal cells of a teleost, Sternarchus albifrons (gymnotoidei)

Junctions between ependymal cells lining the central canal in the spinal cord of the weakly electric teleost, Sternarchus albifrons, were investigated by means of thin-section and freeze-fracture electron microscopy. Junctional complexes representing the ‘terminal bar’ consist of a zonula occludens, followed by intermediate junctions and desmososomes. This pattern is common in many types of epithelia but uncommon in ependyma. Three types of gap junctions were found below the leel of the terminal bar and intermixed with desmosomes: (1) gap junctions at least partially enclosed by a single strand of apparent tight junction, (2) ordinary gap junctions, partially surrounded by a particle-free halo and (3)_segmented gap junctions, in which linear arrays several particles wide are separated by fairly regular linear particle-free regions. Some of the observations may have implications for the mechanism of formation of gap junctions.

Cerebral neuroblastoma

A cerebral neuroblastoma removed surgically from a female child is presented. Electron microscopy showed numerous neuronal processes with growth cones which are a feature of the developing neurone. In addition there were some rosettes with distinct lumina. The luminal surfaces were covered with a smooth plasma membrane lacking any surface differentiation and the lateral surface of these cells had many cell junctions (terminal bars), reminiscent of a primitive neural tube. These features in a nerve cell tumor help to substantiate it as a neuroblastoma arising from immature rather than differentiated cells. The nature of this rare tumor is discussed.

Study of the ultrastructure of the rabbit corneal endothelium by the freeze-fracture technique: Apical and lateral junctions

Freeze-fracture replicas of the rabbit cornea were used to study the spatial structure and the general characteristics of the endothelial cell layer. Between adjacent endothelial cells discontinuous, non-complete occluding junctions were observed which correspond to the junctional elements of the “terminal bar” at the apex of endothelial cells, under the apical folds. They are constituted by rows of interconnected particles on the fracture P-face, and by corresponding furrows on the fracture E-face. On the lateral sides on the cells, there are gap junctions which appear as linear arrays of particles on the P-face and as geometrically arranged complementary pits on the E-face. The apical occluding junctions, as well as the lateral gap junctions are discontinuous, and hence do not constitute a complete barrier for the diffusion of solutes from the anterior chamber into the intercellular spaces.

Scanning electron microscopy of rat maturation ameloblasts.

Post-secretory, maturation-phase ameloblasts were studied by scanning electron microscopy of freeze-fractured or dry-dissected rat incisors. These cells are in contact with the enamel which they secreted at an earlier time and which undergoes a process of continuing mineralization. The lateral intercellular compartment between maturation ameloblasts is sometimes continuous with the intercellular space of the papillary layer of the enamel organ, but often closed by basal ring contacts which correspond to terminal bars seen in transmission electron microscopy. The distal poles of the cells sometimes possess striated borders. Lateral cell surfaces may show longitudinal gutter-like depressions between ridges from which numerous intercellular connections arise; or a maze of lateral folds and ridges; or they may have mostly microvillous surface projections bordering a minimal intercellular space compartment. Preliminary correlations of groupings of basal, lateral and distal cell features indicate that "basal-closed plus distal striated border" cells may show every type of lateral surface. Cell without a striated border, whether open or closed basally, have ridge or maze lateral surfaces bordering a wide intercellular compartment. "Basal-open plus striated border" cells have microvillous or maze-like surfaces. These combinations of features are encountered a few times along the length of the maturation zone of individual incisors and suggest tha existence of cyclical changes in the type of activity of maturation ameloblasts.

Establishment and characteristics of a human pancreatic cancer cell line (HCG-25).

A floating cell line (HCG-25) was established from the metastatic ascitic fluid of a human pancreatic adenocarcinoma of ductal cell origin. The cell line was characterized by the growth in suspension with a doubling time of 15.6 hr, a high cloning efficiency in soft agar and a modal chromosome number of 72. Electron microscopic examination revealed terminal bars in a small number of cells. Production of mucin and immunoglobulins and phagocytosis were not demonstrated. Heterotransplantation of the cells produced tumors, being undifferentiated carcinoma histologically. These characteristics mentioned above confirm that HGC-25 cell line is a human pancreatic cancer cell line.

The fine structure of ducts and subareolar ducts in the resting gland of the female breast.

The ultrastructure of the ducts and subareolar ducts of the resting female breast have been described. In transverse section ducts have longitudinal folds, some of which are solid ridges of cells. Four distinctive cell types were distinguished; epithelial cells, lymphocyte type cells, basal clear cells and myoepithelial cells. The epithelium is single layered, multiple at folds, and similar in general morphology to the terminal ductal-lobular unit. Well developed terminal bars may prevent cellular disruption during contraction, and apical cytoplasmic vesicles represent possible secretory material. Basal cytoplasmic bodies may represent transport of secretory products into or from the periductal stroma. Intranuclear vesicles may also be linked to secretory activity. The myoepithelium is well differentiated with numerous cytoplasmic filaments and 9+0 cilia, forming a discontinuous layer around the epithelium. The basal lamina is generally multilaminate. Capillaries are 1-5mum in diameter and exterior to the delimiting fibroblasts of the epithelial-stromal junction.

Biochemical differentiation of the plasma membrane of the intestinal epithelial cell.

The brush border and basolateral regions of the surface of the intestinal epithelial cell (enterocyte) are exposed to environments which differ even more than those which bathe the different functional regions of the surface of the hepatocyte or the renal tubular cell, and therefore the biochemical differentiation of the enterocyte plasma membrane is also more striking. In addition, it has been easier to study, since the highly adapted brush-border membrane of the enterocyte is one of the easiest of plasma membranes to isolate pure and in quantity (see Isselbacher, 1974). From the study of brush-border preparations a picture has emerged of a membrane with a variety of terminal digestive hydrolases (especially aminopeptidase, disaccharidases and alkaline phosphatase) attached to its luminal surface (Louvard et al., 1975). These are large proteins (Maestracci et al., 1975), which are heavily glycosylated (Kelly & Alpers, 1973; Weiser, 1973; Quaroni et al., 1974) and are moored to the membrane by relatively small hydrophobic polypeptide segments, probably at their N-terminal ends (Maroux & Louvard, 1976). Some of the end-products of digestion that these enzymes generate are then passed across the membrane by transport systems which are closely coupled to the hydrolases and are Na+-independent (Ramaswamy et al., 1976). Some enter the cell via one of several electrogenically driven Na+/solute symport systems (Crane, 1965,1974; Schultz & Curran, 1970; Berger et a[., 1972; Murer & Hopfer, 1974; Hopfer et al., 1973, 1976; Sigrist-Nelson et al., 1976; Alvarado, 1976) and others are taken into the cell by specific transport systems that are independent of Na+ (e.g. fructose; Sigrist-Nelson & Hopfer, 1974). At the cytoplasmic surface of the brush-border membrane, and attached to it by aactinin bridges, is an actin array which forms the microvillus core that also interacts with myosin-like proteins in the terminal web (Mooseker & Tilney, 1975). This raises the exciting, but still largely unexplored, possibility that the brush border is motile (Thuneberg & Rostegaard, 1969; Sandstrom, 1971; Mooseker, 1974) and that this somehow facilitates its digestive and absorptive function, perhaps by preventing the formation of unstirred layers of fluids at either surface of the brush-border membrane. The remainder of the enterocyte plasma membrane (the basolateral region) is separated from the brush border by the terminal bar. Thus, in contrast with the brush border, it interacts with the protective and controlled internal environment of the body and might be expected to be much more similar to the plasma membranes of other cells. It is this region of the plasma membrane which plays the key role in such processes as generating * Present address: Department of Biochemistry, University of Bristol, Medical School, Bristol BS8 1TD. U.K.

Formation of intercellular spaces and junctions in regenerating rabbit corneal endothelium

Rabbit corneal endothelium was destroyed over a diameter of 10 mm using liquid nitrogen applied for 15 sec to the anterior surface. The corneas were afterwards removed at different periods, from 1 day to 2 months and studied by light microscopy after silver impregnation, by transmission electron microscopy, and by scanning electron microscopy in order to study the formation of new intercellular spaces and junctions in the regenerating endothelium. The intercellular spaces and junctions are all reconstituted at the end of the fifth day, when the whole of Descemet's membrane is entirely covered by cells. This period also corresponds to the recovery of the endothelial function. The dynamics of the formation of intercellular spaces are described, and the rapid appearance of two types of junctions as soon as contact between cells is completed. Junctions of the first type, always at the apex of the cells, are single or multiple with adjacent intra-cytoplasmic opacities and correspond to the junctional elements of the “terminal bar”. Junctions of the second type, on the lateral plasma membranes of the cells, are not constantly observed; they are straight, or curved. or circular; their length is variable, and they possess a periodicity in their structure, and correspond to gap junctions.

The cellular organization and nervous supply of the basilar papilla in the lizard, Calotes versicolor.

The basilar papilla of the lizard Calotes versicolor contains about 225 sensory cells. These are of two types: the short-haired type A cells in the ventral (apical) part of the organ, and the type B cells with long hair bundles, in the dorsal (basal) part of the organ. The type A cells are unidirectionally oriented and are covered by a tectorial membrane while the type B cells lack a covering structure and their hair bundles are oriented bidirectionally. Apart from those differences, the type A and type B cells are similar. They are columnar, and display the features common to most sensory cells in inner ear epithelia. The sensory cells are separated by supporting cells, which have long slender processes that keep the sensory cells apart. Close to the surface of the basilar papilla a "terminal bar" of specialized junctions interlocks adjacent cells. Below this adjacent supporting cells are linked by an occluding junction. The cochlear nerve enters from the medial (neural) aspect. The fibres of the nerve lose their myelin sheaths as they enter the basilar papilla. Each sensory cell is associated with several nerve endings. All the nerves identified were afferent. Marked variations were seen between nerve endings in the basilar papilla, but no morphological equivalents of any functional differences were observed.

The ultrastructure of the sensory cells in the chemoreceptor of the ommatophore of Helix pomatia L.

Most of the sensory cells found in the chemoreceptor of the ommatophore of Helix pomatia are typical bipolar cells. The chemoreceptor is deveded by a furrow into two parts; within the ventral subdivision the layer of sensory cell bodiesis thicker than in the dorsal part. According to the differentiations of the apical surface of the dendrites, it is possible to distinguish six different classes: a) dendrites with one cilium and 75 nm thick cytofila (sometimes dendrites of identical appearance posses more than one cilium); b)dendrites with several cilial and 150 nm thick cytofila; c) dendrites with several cilia, 50 nm thick cytofila, and long, striated rootlets; d) dendrites with several cilia bur without cytofila; e) dendrites with 130 nm thick cytofila but without cilia; and f) dendrites with 65 nm thick cytofila but without cilia; dendrites of this class are the only ones with a cytoplasm more electron dense than that of the surrounding supporting cells. All these dendrites are connected to the surrounding supporting cells by terminal bars, each consisting of zonula adhaerens, aonula intermedia and zonula septata. The perikarya of the sensory cells measure approximately 15 mum by 8 mum and enclose 10 mum by 6 mum large nuclei. Axons, originating from these perikarya, extend to the branches of the digital ganglion. In the distal part of this gangloin the axons come into synaptic contact with interneurons, but in our electron micrography it was not possible to coordinate processes and synapses with the corresponding neurons.

The fate and fine structure of fragments of blood vessels in CNS tissue cultures.

Explants from spinal cord, brain stem, cerebellum and cerebral cortex of 5–18 weeks old human embryos and newborn rats were cultivated for 2–30 days. Most of the blood vessel fragments in the explant showed a rather normal structure of their wall even after 30 days in vitro. However, the number of small vessels was reduced. The lumen of most vessels was not collapsed and in some cases filled with cell debris. The endothelial cells remained connected by terminal bars, contained many vesicles and vacuoles of varying size and osmiophilic inclusions of cell debris. While in large vessels the endothelium was always present, in some small vessels near the edge of the explant it was absent. Here, glial endfeet made contact with a basal lamina, which enclosed varying amounts of cell debris. Pericytes were rarely observed after more than 10 days in vitro. Although the perivascular astroglial sheath disintegrated during the first few days in vitro, it was reconstructed and, after about 10 days in vitro, became more complete and differentiated than it was at the time of explantation. Many glial endfeet contained aggregated osmiophilic inclusions. At these sites the perivascular glial sheath and the adhering basal lamina often were discontinuous. The basal laminae were well developed, but disintegrated where the glial sheath was discontinuous. It is concluded that in vitro vessel fragments may be preserved without normal function and basal laminae survive without endothelium.

Electron microscopy of horseradish peroxidase uptake by papillary cells of the mouse incisor enamel organ

Horseradish peroxidase was injected into the tail veins of adult mice. Enamel organs were excised from mice killed at predetermined intervals, fixed in formaldehyde-glutaraldehyde, incubated in diaminobenzidine medium, post-fixed in OsO 4, and processed for electron microscopy. Within 5 min of peroxidase administration, the reaction product was seen extracellularly between papillary cells and between reduced ameloblasts, but not beyond the apical terminal bar apparatus. Only papillary cells took up the peroxidase intracellularly via bristle-coated vesicles. Within the papillary cells, peroxidase was also seen in tubular structures, and at 30–60 min intervals in numerous multivesicular bodies. The results demonstrate that (1) the basal terminal bar apparatus of reduced ameloblasts is permeable to peroxidase, whereas the apical is not, (2) papillary cells function in the absorption of protein from the capillaries, and (3) bristle-coated vesicles and tubular structures serve to transport absorbed protein to multivesicular bodies within papillary cells.

家兎大動脈内皮の培養について

Since Lewis tried to cultuer hepatic endothelium, several authors had reported the in vitro culture of animal endothelium. However, the successive culturing for long time was not performed except by Kitsukawa or Pomerat et al. The author tried to culture the rabbits aortic endothelium in vitro over a year. 0.2% trypsin solution was adopted to gather the endothelial cells from aortic wall. The cells were cultured by 10% fetal calf serum in Eagle medium, and the 8 times “cloning” were done to get a pure strain of the endothelium.1. Cultured endotheliums were asteroid or short fusiform in shape at early stage and changed their shape gradually to fibroblast-like long fusiform types.2. Fibroblasts were also cultured by the same method from rabbits aortic adventitia as the control for cultured endothelium.3. Electron-microscopically, endothelial cells had terminal bars in junctional complex, pinocytotic vesicles and band-like microfilaments which were seen also in human endotheliums.4. The results of C. P. E. test (cytopathic effect test) showed different natures between cultured endothelium and fibroblast (TABLE 1).5. Enzymologically, the cultured endothelium showed marked fibrinolytic activitied which were estimated about 4-5 times greater than that of cultured fibroblast.

Fine structure of rat incisor ameloblasts in transition between enamel secretion and maturation stages

The transitional region (including the end of the secretion zone, the beginning of the maturation zone, and the transition zone between them) was studied in the lower incisor enamel organ of adult rats with the electron microscope. Towards the end of the secretion zone, the surface invaginations of the ameloblasts diminish, the enamel surface becomes smooth and a dense, granulated material appears in the extracellular spaces between ameloblasts. The presence of a 60 Å wide gap between enamel and ameloblasts, and a 100 Å thick enamel border are thought to indicate the end point of enamel secretion and the beginning of the transition zone. Ameloblasts begin to shorten very close to this point. Subsequently, the following events occur: (1) the ameloblast cell membrane lifts away from the enamel to form a 450 Å wide gap; (2) before completion of this gap, a granular material appears in vesicles within the ameloblast apex, possibly to be secreted into the gap; (3) half-desmosomes are formed at the apical cell membrane; (4) the extracellular dense material passes into the spaces between the papillary cells; finally, (5) a coarse-textured material, thought to be enamel constituents being resorbed, appears in the gap, indicating the end of the transition zone. Only following this is the 450 Å gap completed. The attachment sites of both apical and basal terminal bars remain intact throughout the transition zone. The length of the transition zone is about 170 μ. The morphologic features of the transition zone overlap each other and persist for various distances into the maturation zone.

The Scaled Quail (Callipepla squamata) of the Southwest: Systematic and Historical Consideration

brownish or grayish, especially dorsally; abdomen pale with narrow, pale brown markings; size averaging larger. Discussion. Of the four described races of Scaled Quail, hargravei is similar in coloration only to pd the terminal bars of the “scaled” areas are blackish-brown and narrow instead of black and broad. The anterior feathers of the crest are a slightly grayed Saccardo’s Umber, occasionally verging on Sepia rather than Clove Brown and pale Mummy Brown. The belly is nearest Pinkish Buff rather than approaching Cinnamon Buff; the dark bars of the abdominal feathers are grayer, less blackish and less rich, closest to Dresden Brown or Buckthorn Brown X Isabella Color rather than near Tawny Olive or Sayal Brown in pallida. Back, rump, scapulars, and shorter upper tail coverts are brownish-drab, contrasting with the extremely pale gray nape, rather than grayish-drab, not contrasting so conspicuously with the darker bluish nape of pallida. There is no overlap in this character when specimens are segregated by age (and season) as immatures of both races tend to be browner, respectively, than adults, which are grayer. There is considerable variation in mensural characters even when specimens are segregated into their respective age-sex categories. However, specimens of hargravei from Oklahoma, Kansas, Colorado, and northern New Mexico average larger in wing chord, tail, and tarsus than pallida from Arizona and southern New Mexico (see table 1). The few available weights (table 2) also suggest the larger size of the new race.

An ultrastructural analysis of the photoreceptors of the squid and their synaptic connections. I. Photoreceptive and non-synaptic regions of the retina.

AbstractAs part of a larger ultrastructural study on the photoreceptors of the squid, Loligo pealei, this paper reports findings on non‐synaptic regions. The cross‐sectional profiles of individual distal segments coincided in horizontal sections as far as 75 μ apart, but progressively less with greater separations. Areas of cross‐section showed a unimodal distribution skewed towards 6 μ2, the smallest areas. The distribution of ratios of villous to smooth border was unimodal and skewed with 1.0 being the most numerous and minimal ratio. This ratio tended to increase linearly with area. Cells of small cross‐section were completely surrounded by villous border of other cells and about 60° of the perimeter of any cell had microvilli on both sides of the border. Cells participated in odd or even numbers of rhabdomes, up to eight. Pentalaminar membrane junctions between microvilli of the same or neighboring cells were observed. Cytoplasmic microtubules were concentrated near villous borders. In light adaptation some ommin granules entered the photoreceptor tips, and the rhabdomes which formerly began near the surface, now began somewhat below this level. A terminal bar zone existed proximal to the rhabdomes. Here glial cytoplasm separated photoreceptors and both cells contained ommin granules. Photoreceptor somas lacked glial separation and were highly interplicated. Mitochondria were longitudinally arranged along the somal membrane. The planes of the lamellate membrane bodies, seen in the somal cytoplasm of the cells, did not exhibit a rectilinear pattern such as that displayed by the basically rectangular distal segment cross‐sections and microvillar orientations.