The fine structure of the muscle system in the female of the orthonectid Intoshia variabili (Orthonectida)

The contractile system of the female Intoshia variabili (Orthonectida) consists of smooth muscles. The attachment of the longitudinal muscle fibres at the anterior and the posterior tips of the body is rather peculiar, accomplished by means of elongated terminal muscle cells piercing through several ciliated cells. In the last ciliated cell, the muscle cell invaginates the ciliated cell basal membrane almost up to the ciliated cell surface. Here, around the protrusion terminus, there is an electron‐dense zone in contact with the cilia rootlets.     

Surface ultrastructure of the olfactory rosette of an air-breathing catfish,Heteropneustes fossilis (Bloch)

The surface architecture of the olfactory rosette ofHeteropneustes fossilis (Bloch) has been studied by scanning electron microscopy. The olfactory rosette is an oval structure composed of a number of lamellae arranged pinnately on a median raphe. The raphe is invested with epithelial cells and pits which represent goblet cell openings. On the basis of cellular characteristics and their distribution the lateral surface of each olfactory lamella is identified as sensory, ciliated non-sensory and non-ciliated non-sensory epithelium. The sensory epithelium is provided with receptor and supporting cells. The ciliated non-sensory epithelium is covered with dense cilia obscuring the presence of other cell types. The non-ciliated non-sensory epithelium is with many polygonal areas containing cells.     

Ultrastructural studies of normal and alloxan-treated islet cells of the pancreas of the lizard, Eumeces fasciatus

Alpha and beta cells can be distinguished by differences in mitochondrial and secretion granule structure. Many mitochondria of alpha cells possess “tubular” or prismatic cristae oriented longitudinally and having triangular profiles in cross-section. The matrix is particulate, with the roughly spherical particles measuring about 100 A in diameter. Evidence is presented indicating that alpha and beta granules are sequestrated in association with Golgi elements. Fully-condensed beta granules, assumed to be insulin, appear homogeneously dense and crystalline. Recurrent profiles of crystalline beta granules suggest that they possess an octahedral configuration. Alpha cell granules also appear homogeneously dense but have round profiles. Many acinar cell nuclei in both normal and alloxan-treated pancreata display masses of moderately dense fibrils oriented roughly parallel to each other. These fibrils are about 200 A across and their terminal portions are rebranched and often appear to be continuous with the finely granular or filamentous component of the nucleoplasm. Not infrequently the fibrils show evidence of periodicity. Alloxan has a specific destructive effect on beta cells. An initial effect seems to be the disruption and coalescence of the bounding membranes of beta granules. Lysosome-like bodies are often seen in beta cell cytoplasm, which ultimately becomes degranulated and necrotic following prolonged administration of large doses of alloxan.     

Previtellogenic and vitellogenic oocytes in ovarian follicles of cultured siberian sturgeon Acipenser baerii (Chondrostei,Acipenseriformes)

Previtellogenic and vitellogenic oocytes in ovarian follicles from cultured Siberian sturgeon Acipenser baerii were examined. In previtellogenic oocytes, granular and homogeneous zones in the cytoplasm (the ooplasm) are distinguished. Material of nuclear origin, rough endoplasmic reticulum, Golgi complexes, complexes of mitochondria with cement and round bodies are numerous in the granular ooplasm. In vitellogenic oocytes, the ooplasm comprises three zones: perinuclear area, endoplasm and periplasm. The endoplasm contains yolk platelets, lipid droplets, and aggregations of mitochondria and granules immersed in amorphous material. In the nucleoplasm, lampbrush chromosomes, nucleoli, and two types of nuclear bodies are present. The first type of nuclear bodies is initially composed of fibrillar threads only. Their ultrastructure subsequently changes and they contain threads and medium electron dense material. The second type of nuclear bodies is only composed of electron dense particles. All nuclear bodies impregnate with silver, stain with propidium iodide, and are DAPI‐negative. Their possible role is discussed. All oocytes are surrounded by follicular cells and a basal lamina which is covered by thecal cells. Egg envelopes are not present in previtellogenic oocytes. In vitellogenic oocytes, the plasma membrane (the oolemma) is covered by three envelopes: vitelline envelope, chorion, and extrachorion. Vitelline envelope comprises four sublayers: filamentous layer, trabecular layer 2 (t2), homogeneous layer, and trabecular layer 1 (t1). In the chorion, porous layer 1 and porous layer 2 are distinguished in most voluminous examined oocytes. Three micropylar cells that are necessary for the formation of micropyles are present between follicular cells at the animal hemisphere. J. Morphol. 278:50–61, 2017. ©© 2016 Wiley Periodicals,Inc.     

Larval development in <Emphasis Type="Italic">Guancha arnesenae</Emphasis> (Porifera,Calcispongiae, Calcinea)

Larval development and follicle structure of a representative of the Calcinea (Calcispongiae) Guancha arnesenae from the White Sea have been studied for the first time at the ultrastructural level. The follicle in G. arnesenae has an unusual structure: it consists of trapezoid cells rich in phagosomes and a surrounding dense collagen layer. Follicular cells differentiate from choanocytes. Cleavage results in formation of a hollow, equal, non-polarized coeloblastula. Larval morphogenesis occurs by means of direct hollow blastula formation without any individual cell or cell layer movements. The coeloblastula (calciblastula) larva of G. arnesenae is completely ciliated. The larva also contains rare non-ciliated cells: vacuolar cells, bottle-shaped cells and free cells in a central cavity. The basal ciliary apparatus of larval cells includes the basal body, an accessory centriole oriented perpendicularly to it, the basal foot, and two cross-striated rootlets. A bundle of microtubules emerges from the side of the basal body, opposite to the basal foot, running parallel to the outer surface. All bundles of cells are parallel to each other and oriented towards the posterior larval pole, forming a transverse cytoskeletal system. Specialized intercellular junctions in the apical regions of all ciliated cells are revealed for the first time in a Calcispongiae larva. The central larval cavity contains symbiotic bacteria, which are included inside the embryo at the blastula stage.     

Das Epithel der Tuba uterina des Neugeborenen Elektronenmikroskopische Befunde

Summary An electron microscopical study of the epithelium of the uterine tube was carried out in the newborn. Among the epithelial cells at least two morphologically well defined types can be distinguished: ciliated and non-ciliated cells.The ultrastructure of the cilia and related structures corresponds to what has been described by other authors in ciliated cells of various organs and of different species. Near the basal bodies of the cilia there is a concentration of vesicular mitochondria, which is thought to be evidence of a high metabolic activity in this region of the cell. Large opaque granules in the supranuclear zone of the ciliated cells are, it is suggested, paraplasmatic inclusions, perhaps supporting material for the ciliokinetic processes. There was no evidence of a secretory function of the ciliated cells.Among the non-ciliated cells, which in general show a straight lined luminal border with few microvilli, there are some cells containing dense granules, which are distributed throughout the cytoplasm and concentrated in the luminar side of the cell. The apical parts of these cells are protruding and sometimes digitated or branched; they contain accumulated granular materials and are separated from the rest of the cell after the formation of an intracellular plasmalemma. A similar detachment was found in an other cell type, but here the protruded apical parts of the cells are edematous and do not contain any visible secretory materials. It is uncertain if the detached cytoplasmic substances form a part of a specific secretory product; there are no secretory granules within the cytoplasm. On the contrary, the detachment of cytoplasmic parts may only accompany the excessive proliferation of cells which takes place during this period of growth.     

Ultrastructural Observations on the Dwarf Male of Bonellia viridis (Echiura)

The organization of the dwarf male of Bonellia viridis was studied by electron microscopy. The epidermis is formed by two types of epithelial cells: the majority are multiciliated cells; highly vacuolated, non-ciliated cells are less abundant. The body wall musculature consists of an outer circular, a diagonal, and a longitudinal layer. As a unique feature in coelomate spiralians it was found that the perikarya of all muscle cells are located internal to the entire contractile muscular layer. The muscles are solitary myocytes embedded in extracellular matrix. Masses of secretory and indifferent cells occur inside the muscles. Two types of secretory cells were distinguished. Both of them apparently undergo holocrine secretion. A complete lining of thin peritoneal cells delimits the body cavity. Also, the gut and sperm sac have a complete peritoneal lining. The coelomic lining of the gut is a single-layered myoepithelium, that of the sperm sac a pseudo-stratified myoepithelium. The vas deferens was seen to be ciliated. The entrance of the sperm sac is formed by a ciliated funnel that leads into the reservoir by means of a thin, ciliated canal. The existence of repeated transverse nerves and of four longitudinal nerve cords is described for the first time.     

Ultrastructural study of oogenesis in Phoronopsis harmeri (Phoronida)

Temereva, E.N., Malakhov, V.V. and Yushin, V.V. 2011. Ultrastructural study of oogenesis in Phoronopsis harmeri (Phoronida). —Acta Zoologica (Stockholm) 92 : 241–250. The successive stages of oogenesis in Phoronopsis harmeri were examined by electron microscopy methods. During the oogenesis, each oocyte is encircled by vasoperitoneal (coelomic) cells forming a follicle. The previtellogenic oocytes are small cells which accumulate ribosomes for future synthesis; their cytoplasm contains characteristic clusters of mitochondria and osmiophilic particles resembling a germ plasm of other metazoans. The cytoplasm of the vitellogenic oocytes includes numerous mitochondria, cisternae of the rough endoplasmic reticulum, Golgi bodies and annulate lamellae. The synthesis of three types of inclusions was observed: strongly osmiophilic granules (lipid droplets) as a prevalent component, distinctly larger granules surrounded by membrane (proteinaceous yolk) and numerous large vesicles with pale flocculent content. No inclusions which could be unequivocally interpreted as the cortical granules were detected. The surface of the vitellogenic oocytes is covered by microvilli which increase in number and length during development. The oogenesis in Phoronida may be interpreted as follicular because of close association of oocytes with the vasoperitoneal tissue. However, well‐developed synthetic apparatus together with a strongly developed microvillous surface and absence of endocytosis indicate a clear case of autosynthetic vitellogenesis. Thus, in phoronids, there is a combination of simply developed follicle and autosynthesis that, apparently, is plesiomorphic character.     

Bronchiolar pathology. II. Light and electron microscopical changes of bronchiolar epithelial cells in rabbits repeatedly injected intratracheally with a detergent solution

Intratracheal administration in rabbits of a detergent solution (Blue Perlan) determined the progressive swelling of bronchiolar epithelial cells, mainly of non-ciliated secretory ones, with hypertrophy of cytoplasms, frequent bleb ruptures and partial cell necroses. Mucoprotein synthesis was not enhanced. Ultrastructurally, the non-ciliated Clara cells were predominating; their cytoplasms were hypertrophied, prominent in bronchiolar lumina, and contained a few mitochondria and numerous dark-stained secretory granules with a thin membrane; glycogen was present in cytosol, and the apical zones of cytoplasms were locally balloonized; nuclei were chromatin-monomorphous and had an evident membrane. Disrupted blebs presented the same granules and glycogenrich structure as the cytoplasms. Intermingled ciliated cells presented small mitochondria, sometimes modified, and some secretory granules; cilia and basal corpuscles were rarely damaged. Some microvilli intermingled among cilia, but they were extremely rare in non-ciliated secretory hypertrophied cells. Some light junctions were observed between bronchiolar cell cytoplasms. The evolution to partial necrotizing bronchiolitis was obvious mainly after the third intratracheal injection of the detergent solution.     

Fine structure of the developing oocytes in adultArgas (Persicargas) arboreus (Ixodoidea: Argasidae)

The structure of the developing oocytes in the ovary of unfed and fed femaleArgas (Persicargas) arboreus is described as seen by scanning (SEM) and transmission (TEM) electron microscopy. The unfed female ovary contains small oocytes protruding onto the surface and its epithelium consists of interstitial cells, oogonia and young oocytes. Feeding initiates oocyte growth through the previtellogenic and vitellogenic phases of development. These phases can be observed by SEM in the same ovary.The surface of isolated, growing oocytes is covered by microvilli which closely contact the basal lamina investing the ovarian epithelium and contains a shallow, circular area with cytoplasmic projections and a deep pit, or micropyle, at the epithelium side. In more advanced oocytes the shell is deposited between microvilli and later completely covers the surface.Transmission EM of growing oocytes in the previtellogenic phase reveals nuclear and nucleolar activity in the emission of dense granules passing into the cytoplasm and the formation of surface microvilli. The cell cytoplasm is rich in free ribosomes and polysomes and contains several dictyosomes associated with dense vesicles and mitochondria which undergo morphogenic changes as growth proceeds. Membrane-limited multivesiculate bodies, probably originating from modified mitochondria, dictyosomes and ribosomal aggregates, are also observed. Rough endoplasmic reticulum is in the form of annulate lamellae. During vitellogenesis, proteinaceous yolk bodies are formed by both endogenous and exogenous sources. The former is involved in the formation of multivesicular bodies which become primary yolk bodies, whereas the latter process involves internalization from the haemolymph through micropinocytosis in pits, vesicles and reservoirs. These fuse with the primary yolk bodies forming large yolk spheres. Glycogen and lipid inclusions are found in the cytoplasm between the yolk spheres.     

Electron microscopical studies on the thyroid of a cyclostome,Lampetra japonica,during its upstream migration

Summary Electron microscopical studies were made of the thyroid gland of an adult lamprey, Lampetra japonica, in the upstream migration period.The thyroid consists of many usual follicles containing the colloid in their lumina, and a large parafollicle without colloid. The paper concerns only the usual follicle.The follicle cells found in the usual follicle wall are classified into three types; 1. a non-ciliated taller cell, 2. a ciliated taller one, and 3. a non-ciliated cuboidal one. From their cytoplasmic fine structure, it is considered that all these cells are essentially identical and differences among them are due to their functional state.All these type cells are characterized by irregularly developed interdigitations and aggregates of tonofilaments throughout the cytoplasm, especially in the perinuclear region. Although the rough-surfaced endoplasmic reticulum and the Golgi apparatus are fairly well developed in the first and second type cells, the cisternae are not so large-vacuolated but flattened, and the cytoplasm is more compact as compared with that of the higher vertebrate. In the third type cell, the cytomembranes are poorly developed.Large dense inclusion-bodies consisting of heterogeneously dense materials, of lamellar structures, and of less dense vacuoles, which are found often in taller follicle cells, are also characteristic for the lamprey thyroid. The body which might be intimately related to the Golgi apparatus is considered to be a kind of lysosomes and it perhaps corresponds to the yellow pigment observed by light microscopy.In the apical part of the cytoplasm in taller cells, there are three kinds of granules or vesicles; numerous small vesicles considered to be derived from the Golgi apparatus, a few small dense granules which seem to originate from the Golgi region, and a few large less-dense granules.In the third type cell, the cytomembranes are not so well developed as those of the first and second type cells. The large heterogeneously dense bodies and the cytoplasmic granules are very few in number.Around the follicle of the lamprey thyroid, there are a dense basement membrane and a relatively compact connective tissue with few blood capillaries. Characteristic fat cells are found in the connective tissue.     

Electron microscopy of the tracheal ciliated mucosa in rat

Summary The structure of the tracheal epithelial cells from rat has been studied by electron microscopy on approximately 200 Å thick sections with a resolution of better than 30 Å.The epithelium is found to be of a simple columnar type composed of ciliated cells, mucus producing (goblet) cells, basal cells and a fourth kind of cell, here called brush cell. A great number of non-ciliated cells has also been encountered. It has been proved that these represent goblet cells in different stages of intracellular synthesis of mucous granules. The ciliated cells have approximately 8–9 cilia per square micron and there are about 270 cilia on each cell, the calculated surface area being 33 square microns. They are covered by a 70 Å thick membrane. The ciliary filaments are arranged in a pattern of 2 separate ones in the center and a ring of 9 peripheral ones, each divided into 2 subfilaments by a wall with same thickness as the filamentous wall itself, this being 60 Å. The peripheral filaments are continuous with the basal corpuscles. The structure of the corpuscles as compared with earlier findings is discussed. A number of 0.05 micron thick and 1 micron long filiform projections emerge from the cell surface. No cuticle is present.The cell membrane facing adjacent cells is 90 Å and separated from their cell membrane by a 105 Å wide space, this space, being expanded towards a level corresponding to the proximal parts of the cell. A structure that represents terminal bar has been encountered. The cytoplasm is loose and composed of 160 Å thick granules. Spaces enclosed by 50 Å thick membranes with attached 160 Å thick granules (-cytomembranes) are rare. The Golgi zone is analyzed and its regular composition of -cytomembranes, granules and vacuoles is confirmed. The mitochondria with a mean width of 0.23 micron differ to their inner structure from the common type in that the triple layered membranes are highly interconnected. Large opaque granules are encountered in the cytoplasm. Ring-shaped, 850 Å wide, structures are present in the nuclear membrane. The goblet cells are not as abundant as the ciliated cells, the ratio being 14. Small filiform projections covered by a 95 Å thick membrane protrude from the cell surface. This membrane is continuous with the cell membrane, the latter with the same dimensions as in the ciliated cells. Terminal bars are present. The cytoplasm is very opaque due to a dense packing of the 165 Å opaque granules, many in clusters of 4–6. The -cytomembranes have the same dimensions as mentioned above for those present in the ciliated cells. The Golgi zone is of regular composition. There is a suggestion that the Golgi vacuoles and the -cytomembranes are involved in the formation of mucus. In the stage of cellular activity with but few mucous granules, there is a great number of large opaque granules, the size varying from 0.4–1 micron. The mitochondria with a mean width of 0.23 micron have an outer triple layered membrane with a total thickness of 180 Å. The central less opaque layer is 70 Å and the opaque layer on either side is 55 Å. The inner membranes are arranged parallel to each other and have a triple layered composition where the central less opaque layer is 65 Å and the opaque layers each 60 Å. The brush cells belong to the non-ciliated cells. They are encountered singly, surrounded by goblet cells. The surface structures are shaped like brushes or clumsy protrusions which emerge from the distal end of the cell, and are covered by a 95 Å thick membrane. There have been no suggestions of the brushes being cilia in a stage of growth, nor is it probable that they represent stereocilia. They most nearly resemble the intestinal brush border extensions and thus might serve as a resorbing structure.The cytoplasm of the brush cells appears of medium opacity between the ciliated cells and goblet cells and is composed of 155 Å opaque granules. The -cytomembranes are very rare. The Golgi zone is diminutive though of regular composition. The mitochondria are abundant and small with a mean width of 0.14 micron. The outer and inner membranes are triple layered with approximately the same dimensions as reported for the mitochondria of the ciliated and goblet cells. The inner membranes are very few, often only one or two are present. Some of the large opaque granules have inside a very regular arrangement of small 60 Å thick opaque granules arranged in a crystallinic pattern. In the cytoplasm 0.5–1 micron long bundles of 30–40 Å wide fibrils are encountered. The nucleolus shows a characteristic structure of concentrically arranged thin membranes. The basal cells are believed to represent lymphocytes or white blood cells. They sometimes rest on the basement membrane, sometimes are encountered in the distal part of the intercellular spaces. They are bordered by a 110 Å thick cell membrane and have a rather opaque cytoplasm characterized by 160 Å thick opaque granules. A very small Golgi zone is present. The mitochondria, the mean width being 0.14 micron, have triple layered outer and inner membranes, where the less opaque central layer is 65–70 Å and the opaque layers 45–50 Å each. The basement membrane has a thickness of 600 Å. No inner structure has been resolved. The basement membrane is separated from adjacent parts of the ciliated, goblet, brush, and basal cells by a 250 Å wide less opaque space. Below the basement membrane is the lamina propria of the trachea, which is composed of collagen and elastin fibers together with fibroblasts, white blood cells and lymphocytes. The relationship between different types of tracheal epithelial cells in rat has been analyzed. There has been found no indication of a transformation of any type of cells observed into a different type of cell. The development of basal cells via supporting cells or intermediate cells to goblet cells or ciliated cells has not been noticed. On the contrary, all cells that in light microscopy could have been considered to be supporting or intermediate cells, we have been able to recognize as brush cells or as goblet cells to a varying degree filled with mucous granules. If the cells did not seem to reach the cell surface it has been found to be due to a diagonal direction of the sectioning. In this connection it should be emphasized that this relationship is valid only in rat where it is known that the epithelium is of a simple columnar type as distinct from the conditions in man, that epithelium being of a pseudostratified columnar type.This paper is based on a report given at the meeting of Deutsche Gesellschaft für Elektronenmikroskopie in Münster, March 28–31, 1955 and at the Scandinavian Electron Microscope Society Meeting in Stockholm, May 13, 1955.     

Ultrastructure of Pharyngostomoides procyonis Harkema 1942 (Diplostomatidae). II. The female reproductive system

Several components of the female reproductive system of Pharyngostomoides procyonis, including the vitellaria and vitelline duct, ovary and oviduct, Laurer's canal, and Mehlis' gland and associated ducts, were observed with the electron microscope. Vitelline follicles contain cells in various stages of development. Mature vitelline cells contain membrane-delimited clusters of vitelline globules near the plasma membrane. Cilia are present in the vitelline duct. The ovary contains germ cells in various stages of maturation. Oogonia are found in the peripheral region. Mature oocytes contain numerous dense bodies near the plasmalemma. Also included in the cytoplasm of mature oocytes are "nucleolus-like bodies," myelin-like bodies, and mitochondria containing dense granules and few cristae. The epithelium of the oviduct is ciliated. Sperm are present in the oviduct and in Laurer's canal. Two types of secretory cells found in Mehlis' gland are described.     

Embryo development of Corticium candelabrum (Demospongiae: Homosclerophorida)

Abstract. Corticium candelabrum is a homosclerophorid sponge widespread along the rocky Mediterranean sublittoral. Scanning and transmission electron microscopy were used to describe the gametes and larval development. The species is hermaphroditic. Oocytes and spermatocytes are clearly differentiated in April. Embryos develop from June to July when the larvae are released spontaneously. Spermatic cysts originate from choanocyte chambers and spermatogonia from choanocytes by choanocyte mitosis. Oocytes have a nucleolate nucleus and a cytoplasm filled with yolk granules and some lipids. Embryos are surrounded by firmly interlaced follicular cells from the parental tissue. A thin collagen layer lies below the follicular cells. The blastocoel is formed by migration of blastomeres to the morula periphery. Collagen is spread through the whole blastocoel in the embryo, but is organized in a dense layer (basal lamina) separating cells from the blastocoel in the larva. The larva is a typical cinctoblastula. The pseudostratified larval epithelium is formed by ciliated cells. The basal zone of the ciliated cells contains lipid inclusions and some yolk granules; the intermediate zone is occupied by the nucleus; and the apical zone contains abundant electron-lucent vesicles and gives rise to cilia with a single cross-striated rootlet. Numerous paracrystalline structures are contained in vacuoles within both apical and basal zones of the ciliated cells. Several slightly differentiated cell types are present in different parts of the larva. Most cells are ciliated, and show ultrastructural particularities depending on their location in the larvae (antero-lateral, intermediate, and posterior regions). A few smaller cells are non-ciliated. Several features of the C. candelabrum larva seem to support the previously proposed paraphyletic position of homoscleromorphs with respect to the other demosponges.     

The fine structure of the secretory cells of the uterus (shell gland) of the chicken

The secretory processes in the shell gland of laying chickens were the subject of this study. Three cell types contribute secretory material to the forming egg: ciliated and non-ciliated columnar cells of the uterine surface epithelium, and cells of tubular glands in the mucosa. The ciliated cells as well as the non-ciliated cells have microvilli, which undergo changes in form and extent during the secretory cycle. At the final stages of shell formation they resemble stereocilia. It is postulated that the microvilli of both cells are active in the production of the cuticle of the shell. The ciliated cell which has both cilia and microvilli manufactures secretory granules which arise from the Golgi complex in varying amounts throughout the egg laying cycle. Granule production reaches its greatest intensity during the early stages of shell deposition. The ciliated cell probably supplies proteinaceous material to the matrix of the forming egg shell. The non-ciliated cell has only microvilli. Secretory granules, containing an acid mucopolysaccharide, arise from the Golgi complex. Some granules are extruded into the uterine lumen where they supply the egg shell with organic matrix. Others migrate towards the supranuclear zone. Here a number of them disintegrate. This is accompanied by the formation of a large membraneless space, which is termed “vacuoloid.” Subsequently the vacuoloid regresses and during regression an extensive rough endoplasmic reticulum with numerous polyribosomes of spiral configuration appears. It is suggested that material in the vacuoloid originating from the disintegrating granules is resynthesized and utilized for the formation of secretory product. The uterine tubular gland cells have irregular, frondlike microvilli. During egg shell deposition, these microvilli form large blebs and are probably related to the elaboration of a watery, calcium-containing fluid.     

Histochemical and ultrastructural features of the epidermis of the land planarian Bipalium adventitium

The epidermis of the land planarian Bipalium adventitium was examined by light and electron microscopy. In all regions, the epidermis consists of a simple columnar ciliated epithelium associated with a prominent basement membrane. The epithelial cells, possessing abundant microvilli and poorly developed terminal webs, are conjoined laterally at their apical ends by septate junctions. The epidermis of the creeping sole is distinguished from that of adjoining regions by a “insunken” condition of the epithelial cells, a greater number of cilia per cell, and an absence of glandular secretions other than mucus. The insunken cells of the sole possess large glycogen disposits and attributes of metabolically active cells. Unusual intranuclear inclusions of unknown significance are also found in many of the epidermal cells in all regions. The basement membrane lacks distinct layering and consists of fine fibrils displaying a beaded appearance but no obvious cross-banding. Histochemical tests indicate that the fibrils are collagenous. In addition to mucus, secretory material found in nonsole regions includes lamellated granules and rhabdites, both stained intensely by acidic dyes. Rhabdites and the basement membrane also contain disulfide-enriched proteins. In scanning electron micrographs, the sole appears as a faint, longitudinally oriented band extending along the entire length of the animal. In all regions except the sensory border of the head, the microvilli are generally obscured by the densely arranged cilia. The sensory border consists of a row of toothlike papillae and grooves covered almost exclusively by microvilli, small club-shaped structures, and larger spherical protrusions.     

Morphometric and ultrastructural features of the mare oviduct epithelium during oestrus

Morphometric, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations have displayed regional differences in the mare oviductal epithelium. The entire mucosa of the oviduct was lined with a pseudostratified epithelium, which consisted of two distinct cell types, ciliated and non-ciliated. Ciliated cells were predominant in the three different segments of the oviduct and their percentage increased from fimbriae to ampulla and significantly decreased in the isthmus. SEM revealed in the infundibulum finger-like mucosal folds, some of them interconnected, in the ampulla numerous and elaborated branched folds of the mucosa, whereas the isthmus displayed a narrow lumen, short and non-branched mucosal folds. In the ampulla and isthmus the majority of non-ciliated cells showed apical blebs provided or not of short microvilli. TEM displayed different ultrastructural features of ciliated and non-ciliated cells along the oviduct. Isthmus ciliated cells presented a more electron-dense cytoplasm than in infundibulum and ampulla cells and its cilia were enclosed in an amorphous matrix. The non-ciliated cells of infundibulum did not contain secretory granules but some apical endocytic vesicles and microvilli coated by a well developed glycocalyx. Non-ciliated cells of ampulla and isthmus contained secretory granules. Apical protrusions of ampulla displayed two types of secretory granules as well as occasional electron-lucent vesicles. Isthmus non-ciliated cells showed either electron-lucent or electron-dense cytoplasm and not all contained apical protrusions. The electron-dense non-ciliated cells displayed microvilli coated with a well developed glycocalyx. Three types of granules were observed in the isthmus non-ciliated cells. The regional differences observed along the epithelium lining the mare oviduct suggest that the epithelium of the each segment is involved in the production of a distinctive microenvironment with a unique biochemical milieu related to its functional role.     

Ciliary activity in the mouse oviduct as studied by transmission and scanning electron microscopy

The mouse oviduct is covered by dense tracts of ciliated cells interspersed at random with occasional non-ciliated cells. Correlation between scanning electron microscopy and thin section images indicates that in the isolated fimbria most cilia are short (5 µm) and inactive, resting at the end of a uterad-directed effective stroke. These cilia terminate in a 9S−2 tip, the microtubules ending in an electron-dense plaque underneath the cell membrane. At the tip of the cilium a crown of fine extracellular hairs is attached to the ciliary membrane. In the ampulla and isthmus the ciliated cells decrease progressively in number and appear to lie in crypts.     

Ultrastructure of the Penicillate Podia of the Spatangoid Echinoid Echinocardium cordatum (Echinodermata) with Special Emphasis on the Epidermal Sensory-Secretory Complexes

The spatangoid echinoid Echinocardium cordatum possesses specialized penicillate podia that handle sediment particles during burrowing and feeding. Epidermal complexes, which occur on podial surfaces directly contacting the sediment, each comprise four cells: a non-ciliated secretory cell containing granules rich in mucopolysaccharides (NCS cell), a ciliated secretory cell containing granules of unknown composition (CS cell), and two ciliated non-secretory cells (CNS cells). The cilium of the CS cell is subcuticular whereas that of each CNS cell traverses the cuticle. We propose that these four cells constitute a sensory-secretory complex wherein the ciliated cells are sensory cells and the secretory cells function for adhesion and de-adhesion. More exactly, an NCS cell adhesive and a CS cell de-adhesive would be sequential and would be initiated by two successive stimulations transduced by cilia when the podium touches the sediment. Cilia that first contact the sediment are those protruding through the cuticle from the CNS cells. Their stimulation would result in the secretion of an adhesive material by the NCS cells. Subsequently, the subcuticular cilia of CS cells would be stimulated when the podial digitations closely squeeze the substrate, and this would induce the secretion of a de-adhesive. These two antagonistic secretions would allow the podium to pick up and discharge sediment repetitively during burrowing and feeding.     

Ultrastructural, histochemical and cytochemical characterization of intestinal epithelial cells in Aplysia depilans (Gastropoda, Opisthobranchia)

To improve the current knowledge about the digestive system in opisthobranchs, light and electron microscopy methods were used to characterize the epithelial cells in the mid‐intestine of Aplysia depilans. This epithelium is mainly formed by columnar cells intermingled with two types of secretory cells, named mucous cells and granular cells. Columnar cells bear microvilli on their apical surface and most of them are ciliated. Mitochondria, multivesicular bodies, lysosomes and lipid droplets are the main components of the cytoplasm in the region above the nucleus of these cells. Peroxisomes are mainly found in middle and basal regions, usually close to mitochondria. Mucous cells are filled with large secretory vesicles containing thin electron‐dense filaments surrounded by electron‐lucent material in which acidic mucopolysaccharides were detected. The basal region includes the nucleus, several Golgi stacks and many dilated rough endoplasmic reticulum cisternae containing tubular structures. The granular cells are characterized by very high amounts of flat rough endoplasmic reticulum cisternae and electron‐dense spherical secretory granules containing glycoproteins. Enteroendocrine cells containing small electron‐dense granules are occasionally present in the basal region of the epithelium. Intraepithelial nerve fibres are abundant and seem to establish contacts with secretory and enteroendocrine cells.