Elektronenmikroskopische Untersuchungen anAnaitides mucosa (Annelida,Polychaeta). Cuticula und Cilien,Schleimzellen und Schleimextrusion

Two components, a basal cuticle and an epicuticle, make up the cuticle ofA. mucosa. The basal cuticle consists of collagen fibrils, which are arranged in about 20 layers. The orientation of the fibrils changes rectangularly from one layer to the next. Fine filaments interweave the basal cuticle. The epicuticle, which is covered by a layer of electron dense material, is composed of irregularly arranged thin filaments. Branched microvilli of the epidermal cells penetrate the cuticle. Bacteria are found in the basal cuticle. Dorsally each segment has a band of densely packed smooth cilia. Laterally and partly ventrally aggregates of cilia are observed. These cilia exhibit apically artificial swellings. At least six different mucous cells are observed in the epidermis, morphologically distinguishable by the structure of the secretion products. Mucus is secreted via exocytosis through cuticular pores. During this process the mucus might expand. The secreted mucus consists of filamentous subunits.     

Fine Structure of the Tentacles of Phoronis australis Haswell (Phoronida,Lophophorata)

The epidermis of the tentacles of Phoronis australis consists of six cell types: supporting cells, choanocyte-like sensory cells, both types monociliated, secretory A-cells with a mucous secretion, and three kinds of B-cells with mucoprotein secretions. On cross-sections of the tentacle, one can distinguish four faces: the frontal one, heavily ciliated and located between the two frontolateral rows of sensory cells, the lateral and the abfrontal ones. The orientation of the basal structures of the cilia is related to the direction of their beat. The basiepidermal nervous system is grouped mainly at the frontal and abfrontal faces. The basement membrane is thickest on the frontal face and consists of circular collagen fibrils near the epidermis and longitudinal ones near the peritoneum. All peritoneal cells surrounding the mesocoel are provided with smooth longitudinal myofibrils, and isolated axons are situated between these cells and the basement membrane. The wall of the single blood capillary in each tentacle consists of epitheliomuscular cells with circular myofilaments, lying on a thin internal basal lamina; there is no endothelium.     

Fine structure of the cephalic sensory organ in veliger larvae of Littorina littorea, (L.) (Mesogastropoda,Littorinidae)

The cephalic sensory organ (CSO) in planktonic veliger larvae of Littorina littorea is situated dorsally between the velar lobes at the level of the shell aperture. It consists of ciliated primary sensory cells, adjacent accessory cells and supporting epithelial cells. Cell bodies of the ciliated cells originate in the cerebral commissure and their dendrites pass to the epidermis. The flask-shaped sensory cells are characterized by a deep invaginated lumen with modified cilia arising from the cell surface in the lumen. These cilia are presumed to be non-motile because they lack striated rootlets and show a modified microtubular pattern (6 + 2, 7 + 2 and 8 + 2). The adjacent accessory cells never possess an invaginated lumen; occasionally cilia and branched microvilli arise from the apical surface. These cells may be sensory, but there is no obvious direct connection with the nervous system. The supporting epithelial cells are part of the epidermis and flank the apical necks of the sensory and accessory cells. Morphological evidence suggests that the CSO may function in chemoreception related to substrate selection at settlement, feeding or other behaviour.     

The fine structure of the buccal tentacles of Holothuria forskali (Echinodermata,Holothuroidea)

Summary Ultrastructural study of the buccal tentacles of Holothuria forskali revealed that each tentacle bears numerous apical papillae. Each papilla consists of several differentiated sensory buds.The epidermis of the buds is composed of three cell types, i.e. mucus cells, ciliated cells, and glandular vesicular cells (GV cells). The GV cells have apical microvilli; they contain bundles of cross striated fibrillae associated with microtubules. Ciliated cells have a short non-motile cilium. Bud epidermal cells intimately contact an epineural nervous plate which is located slightly above the basement membrane of the epidermis. The epineural plate of each bud connects with the hyponeural nerve plexus of the tentacle. This nerve plexus consists of an axonic meshwork surrounded in places by sheath cells. The buccal tentacles have well-developed mesothelial muscles. Direct innervation of these muscles by the hyponeural nerve plexus was not seen.It is suggested that the buccal tentacles of H. forskali are sensory organs. They would recognize the organically richest areas of the sediment surface through the chemosensitive abilities of their apical buds. Tentacles presumably trap particles by wedging them between their buds and papillae.     

Ultrastructure of the kidney of a South American caecilian,Typhlonectes compressicaudus (Amphibia,Gymnophiona)

The ultrastructure of the renal corpuscle, the neck segment, the proximal tubule and the intermediate segment of the kidney of a South American caecilian, Typhlonectes compressicaudus (Amphibia, Gymnophiona) was examined by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and freeze-fracture technique. The glomerular filter apparatus consists of the podocyte epithelium, a distinct basement membrane, a subendothelial space and the capillary endothelium. Emanating from the podocyte cell body, several long primary processes encircle neighboring capillaries. The short slender foot processes originating from the primary processes interdigitate with those from other primary processes, thereby forming the meandering filtration slit. Thick bundles of microfilaments are found in the primary processes, but absent in the foot processes. The basement membrane consists of a lamina rara externa and a rather thin lamina densa (50 nm thickness). The wide subendothelial space contains abundant microfibrils, a few collagen fibrils and many thin processes of mesangial cells. The endothelium is flat and fenestrated (compared to mammals displaying relatively few fenestrations); some of the fenestrations are bridged by a diaphragm. The glomerular mesangium is made up of the mesangial cells and a prominent mesangial matrix containing microfibrils and collagen fibrils. The cells of the neck and intermediate segments display numerous cilia with their microtubules arranged in the typical 9 + 2 pattern. The basal bodies of the cilia are attached to thick filaments with a clear crossbanding pattern of 65 nm periodicity. The proximal tubule is composed of cells typical for this segment (PT cells) and light cells lacking a brush border (bald-headed cells). The PT cells measure 10-25 micron in height and 15-30 micron in width and do not interdigitate at their lateral borders with each other. Their basolateral cell membrane is amplified by many folds projecting into lateral intercellular spaces and into basal recesses. The brush border is scarce and composed of loosely arranged short microvilli.     

Ultrastructure of the supporting cells in the chemoreceptor areas of the tentacles of Pomatias elegans (Müller) (mollusca,prosobranchia) and the ommatophore of Helix pomatia L. (Mollusca,Pulmonata)

The ultrastructure of the supporting cells in the chemoreceptor areas of the tentacles of Pomatias elegans and Helix pomatia is very similar. Complex apical structures are present, and the lateral plasma membrane exhibits three zones: (1) a zone of slight interdigitations; (2) a zone characterized by longitudinal plicae; (3) a zone of basal radiculae. The portions of the sensory cells located within the epithelial layer are accommodated in longitudinal grooves in the supporting cells. However, there are also differences. In Pomatias elegans the apical surface is differentiated into long microvilli that are sometimes dichotomously branched and invested by a surface coat along their entire length. Cytofilia and cilia of the sensory cells pass through this layer of microvilli and surface coat throughout its entire width. In Helix pomatia the supporting cells are somewhat smaller and the apical differentiation consists of candelabra-like protrusions, which are usually three times dichotomously branched. The final branchings, corresponding to microvilli, are called terminal twigs. They are covered by a surface coat, which forms a feltwork. The cytofilia and cilia of the sensory cells that intertwine among the protrusions are confined to the space below the terminal twigs, where they compose the spongy layer.     

The structures of the tentacles of Rhabdopleura compacta (Hemichordata) with special reference to neurociliary control

Summary The tentacle of Rhabdopleura compacta (Hemichordata) consists of two layers of cells surrounding a central coelomic cavity. The two layers of cells are separated by a cell free basement lamella.The tentacles on the arms of Rhabdopleura bear three longitudinal rows of cilia. The ciliated cells are closely associated with bundles of nerve fibres, and between some of the cells and nerve fibres there are synapses. The peripheral regions of the ciliated cells are joined to one another by desmosomes. Tonofibrils join some of these desmosomes to the kinetosomes of the cilia.The nerve fibres are confined to the ectodermal layer and the muscle cells to the layer of cells within the basement lamella. In the ectodermal layer besides ciliated cells there are mucus cells, densely pigmented cells, and green bodies. The function of these last two types of cells is secretory. Most of the epithelial cells have microvilli upon their free borders.I wish to thank Professor J. Z. Young F. R. S. for enthusiastic advice and encouragement. Dr. R. Bellairs generously provided the facilities for electron microscopy. Mr. R. Moss gave excellent technical and photographic assistance. Dr. A. Stebbing of the Plymouth Marine Biological Laboratory helped me to obtain and to identify the specimens. Professor D. W. James kindly allowed me to use his facilities for interference microscopy.     

Structure of the digestive tract of tornaria larva inEnteropneusta (Hemichordata)

The ultrastructure of the digestive tract of tornaria larva of enteropneusts was investigated. It showed that the digestive tract consists of three parts: esophagus, stomach, and intestine. The esophagus epithelium consists of two types of multiciliated epithelial cells and solitary muscle cells. Axonal tracts and neurons were found in the ventral wall of the esophagus. The cardiac sphincter contains an anterior band of strongly ciliated cells and a posterior band of cells with long vacuolized processes which partition the sphincter lumen. The stomach consists of three cell types: (1) cells with electron-opaque cytoplasm, bearing a fringed border on their apical sides; (2, 3) sparse cells with electron-light cytoplasm and different patterns of apical microvilli. Cells of the pyloric sphincter bear numerous cilia and almost no microvilli. The intestine consists of three parts. The anterior part is formed of multiciliated cells which bear the fringed border. The middle part consists of flattened cells bearing rare cilia and vast numbers of mace-like microvilli. The posterior part of the intestine is formed of cells bearing numerous cilia and few microvilli. Muscle cells were not found in either stomach or intestine epithelium. One noticed that the structure of the digestive tract of enteropneust tornaria larva differs from that of echinoid pluteus larva.     

Ultrastructural evidence for multiple mucous domains in frog olfactory epithelium

Summary This study showed that the olfactory mucus is a highly structured extracellular matrix. Several olfactory epithelial glycoconjugates in the frog Rana pipiens were localized ultrastructurally using rapid-freeze, freeze-substitution and post-embedding (Lowicryl K11M) immunocytochemistry. Two of these conjugates were obtained from membrane preparations of olfactory cilia, the glycoproteins gp95 and olfactomedin. The other conjugates have a carbohydrate group which in the olfactory bulb appears to be mostly on neural cell-adhesion molecules (N-CAMs); in the olfactory epithelium this carbohydrate is present on more molecules. Localization of the latter conjugates was determined with monoclonal antibodies 9-OE and 5-OE. Ultrastructurally all antigens localized in secretory granules of apical regions of frog olfactory supporting cells and in the mucus overlying the epithelial surface, where they all had different, but partly overlapping, distributions. Monoclonal antibody 18.1, to gp95, labeled the mucus throughout, whereas poly- and monoclonal anti-olfactomedin labeled a deep mucous layer surrounding dendritic endings, proximal parts of cilia, and supporting cell microvilli. Labeling was absent in the superficial mucous layer, which contained the distal parts of the olfactory cilia. Monoclonal antibody 9-OE labeled rather distinct areas of mucus. These areas sometimes surrounded dendritic endings and olfactory cilia. Monoclonal antibody 5-OE labeled membranes of dendritic endings and cilia, and their glycocalyces, and also dendritic membranes.     

Ultrastructure of multiciliated collar cells in the pilidium larva of Lineus bilineatus (Nemertini)

Summary The ultrastructure of the apical plate of the free-swimming pilidium larva of Lineus bilineatus (Renier 1804) is described with particular reference to the multiciliated collar cells. In the multiciliary collar cells there are several, up to 12, cilia surrounded by a collar of about 20 microvilli extending from the cells' apical surface. The cilia have the typical 9+2 axoneme arrangement and are equipped with striated caudal rootlets extending from the basal bodies. No accessary centriole or rostral rootlet were observed. Microvilli surrounding the cilia are joined in a cylindrical manner by a mucus-like substance to form a collar. In comparison with many sensory receptor cells built on a collar cell plan the multiciliary collar cells of the pilidium larva apical plate are rather simple and unspecialized. In other pilidium larvae monociliated collar cells are found in the apical plate. The possible function and phylogenetic implications of multiciliated collar cells in Nemertini are briefly discussed.List of Abbreviations a axoneme - b basal body - c cilia or flagella - d desmosome - G Golgi apparatus - m mitochondria - mf microfilaments - mu mucus - mv microvilli - n nucleus - nt neurotubules - pm plasma membrane - r rootlet - ri ribosomes - v secretory vesicles     

Comparative morphology of the epidermis of seven species of polyclad flatworms (Platyhelminthes: Rhabditophora)

The ultrastructure of the epidermis of seven species of polyclad flatworms (Phaenocelis medvedica, Phaenocelis peleca, Pleioplana atomata, Boninia divae, Pericelis orbicularis, Enchiridium periommatum, and Cycloporus variegatus) representing six families is described. In all seven species, the epidermis consists of a single layer of columnar cells that rests on a bipartite basement membrane. Epithelial cell surfaces are covered by numerous microvilli and cilia. Cilia contain microtubules arranged in the 9 + 2 pattern, and from their basal bodies two striated rootlets arise, a rostrally directed one running parallel to the apical cell membrane, and a vertical one at a right angle to the first rootlet. Numerous epithelosomes and mitochondria occupy the apical parts of the cells. The basal part of the cells is highly folded, forming a cell web that connects to the basement membrane. The basement membrane consists of a thin basal lamina and a thick, multilayered reticular lamina. The number of layers in the reticular lamina varies among the different species and appears to be correlated with body size. Numerous canals containing either pigment granules or nervous processes perforate the basement membrane. We have identified four different types of glands: rhabdite glands, rhabdoid glands, mucoid glands containing vacuoles filled with flocculent material, and mucoid glands resembling thread cells of hagfish slime glands. The latter have been found only in P. orbicularis. Pigment cells were found in all species examined with the exception of C. variegatus, which takes its coloration from its ascidian prey. Our results further support the unique taxonomic status of Boniniidae.     

Freeze-fracture study of the receptor membranes in the olfactory organ of Alburnus alburnus (Teleostei)

Summary Olfactory receptor molecules are assumed to be integral membrane proteins which may be visualized on fracture faces of the membrane as intramembrane particles (IMPs). In the present study, the plasma membrane of the receptor dendrites and ciliated epithelial cells in the teleost fish Alburnus alburnus were studied by freeze-fracture electron microscopy. The IMP diameters on the membrane P-faces of both receptor dendrites and ciliated epithelial cells ranged from 5 nm to 11 nm. The average IMP densities on membrane fracture faces of the ciliated and microvillous sensory dendrites were 3130±780 for the cilia, 2070±550 for the microvilli, 2390±1190 on the knob regions and 3050±1130/m on the lateral dendrite membranes. The IMP densities on the P fracture faces of the cilia and knob regions were compared with the densities found on the lateral membranes of each individual dendrite. The ratios ranged from 0.5 to 0.96 in the case of the cilia/lateral membrane and from 0.5 to 0.90 in that of the knob/lateral membrane, indicating that, in contrast to the average densities, it is the lateral membrane which has the higher IMP densities and not the cilia. The great variations in the average IMP densities, as well as the considerable variety of the ratios, may be explained by the maturation and turnover of the olfactory sensory neurons.     

The distribution of dopamine-like immunoreactivity in the thoracic and abdominal ganglia of the locust (Schistocerca gregaria)

Summary An indirect gold-labeling method utilizing the lectin from Limax flavus was employed to characterize the subcellular distribution of sialic acid in glycoconjugages of the salamander olfactory mucosa. The highest density of lectin binding sites was in secretory vesicles of sustentacular cells. Significantly lower densities of lectin binding sites were found in secretory granules of acinar cells of both Bowman's and respiratory glands. Lectin binding in acinar cells of Bowman's glands was confined primarily to electron-lucent regions and membranes of secretory granules. In the olfactory mucus, the density of lectin binding sites was greater in the region of mucus closest to the nasal cavity than in that closest to the epithelial surface. At the epithelial surface, the density of lectin binding sites associated with olfactory cilia was 2.4-fold greater than that associated with microvilli of sustentacular cells or non-ciliary plasma membranes of olfactory receptor neurons, and 7.9-fold greater than non-microvillar sustentacular cell plasma membranes. Lectin binding sites were primarily associated with the glycocalyx of olfactory receptor cilia. The cilia on cells in the respiratory epithelium contained few lectin binding sites. Thus, sialylated glycoconjugates secreted by sustentacular cells are preferentially localized in the glycocalyx of the cilia of olfactory receptor neurons.     

An Electron Microscopic Study of the Intestinal Villus : I. The Fasting Animal

The structure of the intestinal villus of the rat was studied in thin sections of tissue fixed in buffered osmium tetroxide and embedded in methacrylate. The simple columnar epithelium investing the villus is surmounted by a striated border consisting of slender projections of the cell surface. These microvilli are arranged in almost crystalline, hexagonal array, and increase the apical surface area of the cell by a factor of 24. The core of each microvillus is filled with fine fibrils which arise from the filamentous substance of the terminal web underlying the striated border. Each microvillus is covered by a tubular extension of the plasma membrane of the epithelial cell. Pinocytotic vesicles originating from the plasma membrane occur at the bases of the intermicrovillous spaces. The nucleus, mitochondria, and the endoplasmic reticulum of the epithelial cell display no unusual features. Small bits of ergastoplasm occur in the apical cytoplasm. A thin basement membrane separates the epithelium from the lamina propria which consists of vessels, nerves, and numerous lymphocytes, eosinophiles, mast cells, plasma cells, smooth muscle fibers, and macrophages suspended in a delicate stroma of fibroblasts and collagen fibers. Intercellular fat droplets often occur in this stroma, even in animals fasted for 40 hours. The blood capillaries are distinguished by their extremely attenuated, fenestrated endothelial cells. The lacteal has a thicker endothelium which, although not fenestrated, appears to have significant interruptions, especially at the margins between neighboring lining cells. Strands of smooth muscle always accompany the lacteal but do not form an integral part of its wall. Unmyelinated nerves, many of which are too small to be distinguished with the light microscope, course through the lamina propria in association with the vessels. The nerve fibers evidently do not cross the basement membrane into the epithelium. Neuromuscular junctions or other terminal apparatus were not found.     

Polyvillous cells of the epidermis: transportive elements of lamprey skin

Polyvillous cells are differentiated bipolar cells in the epidermis of Lampetra spp., which are not innervated and are interpreted as a type of ionocyte. They bear numerous apical microvilli, capped by mucus. In some examples the apex bulges at the surface of the epidermis, in others it is sunken into a crypt or may even appear to be internal to the cell. It is supposed that these variations correlate with the maturity of the individual cell. Cytological features aiding recognition of the polyvillous cells by electron microscopy are the presence of numerous membrane fragments in the secretion above the short irregular apical microvilli, coated apical invaginations or vesicles, mitochondria with well developed cristae and internal granules, and in many cases a plasma membrane which appears more electrondense than that of the neighbouring epithelial cells     

Surface fine structure of the globiferous pedicellariae of the regular echinoid,Psammechinus miliaris gmelin

The globiferous pedicellariae of Psammechinus miliaris are described. Two fixation methods giving minimal distortion and rapid tissue hardening were adapted for soft tissue preparation for scanning electron microscopy. The pedicellarial valves are covered by a microvillous epithelium. The outer valve epithelial microvilli overlying red spherulocytes in the epidermis are characterized by a filament matrix radiating out from each microvillus. These microvilli may function in epidermal absorption of organic solutes. The inner valve microvilli are more densely packed and the filament matrix is absent. Ciliation is confined to the inner valve surface where the cilia are concentrated to form a distal sensory pad and sensory hillock. Behavioural evidence suggests a chemo- and mechanosensory role for the inner valve surface.     

An electron microscopic study of the intestinal villus. I. The fasting animal

The structure of the intestinal villus of the rat was studied in thin sections of tissue fixed in buffered osmium tetroxide and embedded in methacrylate. The simple columnar epithelium investing the villus is surmounted by a striated border consisting of slender projections of the cell surface. These microvilli are arranged in almost crystalline, hexagonal array, and increase the apical surface area of the cell by a factor of 24. The core of each microvillus is filled with fine fibrils which arise from the filamentous substance of the terminal web underlying the striated border. Each microvillus is covered by a tubular extension of the plasma membrane of the epithelial cell. Pinocytotic vesicles originating from the plasma membrane occur at the bases of the intermicrovillous spaces. The nucleus, mitochondria, and the endoplasmic reticulum of the epithelial cell display no unusual features. Small bits of ergastoplasm occur in the apical cytoplasm. A thin basement membrane separates the epithelium from the lamina propria which consists of vessels, nerves, and numerous lymphocytes, eosinophiles, mast cells, plasma cells, smooth muscle fibers, and macrophages suspended in a delicate stroma of fibroblasts and collagen fibers. Intercellular fat droplets often occur in this stroma, even in animals fasted for 40 hours. The blood capillaries are distinguished by their extremely attenuated, fenestrated endothelial cells. The lacteal has a thicker endothelium which, although not fenestrated, appears to have significant interruptions, especially at the margins between neighboring lining cells. Strands of smooth muscle always accompany the lacteal but do not form an integral part of its wall. Unmyelinated nerves, many of which are too small to be distinguished with the light microscope, course through the lamina propria in association with the vessels. The nerve fibers evidently do not cross the basement membrane into the epithelium. Neuromuscular junctions or other terminal apparatus were not found.     

Glycosaminoglycans in porcine lung: an ultrastructural study using Cupromeronic Blue

Glycosaminoglycans (GAGs) are essential components of the extracellular matrix contributing to the mechanical properties of connective tissues as well as to cell recognition and growth regulation. The ultrastructural localization of GAGs in porcine lung was studied by means of the dye Cupromeronic Blue in the presence of 0.3 M MgCl₂ according to Scott's critical electrolyte concentration technique. GAGs were observed in locations described as follows. Pleura: Dermatan sulphate (DS) and chondroitin sulphate (CS) attached in the region of the d-band of collagen fibrils, interconnecting the fibrils; heparan sulphate (HS) at the surface of elastic fibers and in the basement membrane of the mesothelium and blood vessels. Bronchial cartilage: Abundant amounts of GAGs were observed in three zones: pericellular, in the intercellular matrix and at the perichondrial collagen. By enzyme digestion a superficial cartilage layer with predominantly CS could be distinguished from a deep zone with CS and keratan sulphate. The structure of the large aggregating cartilage proteoglycan was confirmed in situ. Airway epithelium: HS at the whole surface of cilia and microvilli and in the basement membrane of the epithelial cells. Alveolar wall: CS/DS at collagen fibrils, HS at the surface of elastic fibers and in the basement membranes of epithelium and endothelium.     

The relief characteristics of the apical cell surface of endometrial epitheliocytes in women suffering from sterility]

Functional changes in the surface topography of the uterus in women of reproductive age have been studied using scanning electron microscopy. The state of the cell surface relief was estimated at different phases of the menstrual cycle and in sterile women. The presence of wide and short ruffles of epithelial cells covered with mucus is typical of the secretory phase of the cycle. No microvilli or cilia are seen on the epitheliocyte surface. In contrast, the follicular phase is characterized with numerous deep ruffles of epithelium covered with cylindrical cells. The apical surface is studded with numerous microvilli and cilia persisting even in sterile women at all the stages of the cycle. The disturbances of nidation processes in the fertilized ovule may apparently be associated with the patterns of the cell surface relief.     

Ultrastructural features of the epidermis of the planarian Artioposthia triangulata (Dendy)

The epidermis of the land planarian Arthioposthia triangulatawas examined by scanning and transmission electron microscopy. Thisinvestigation revealed that the flatworm was covered entirely withcilia and was especially densely populated on the ventral surface.In all regions the epidermis consisted of a one-layered columnarepithelium resting on a prominent basement membrane, but lacking aterminal web. Various secretions were found in the epidermistogether with epidermal rhabdoids. Below the basement membraneother secretory material was visible and this included thecytoplasmic lamellated granules and adenal rhabdites. The basementmembrane consisted of fibrils with a beaded appearance and thesewere arranged parallel to the epidermal layer but did not displaycross-banding. The secretory cells above and below the basementmembrane were compared and their products characterized on thebasis of shape, size and location. Their possible function isdiscussed.