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.     

"Light" epithelial cells of swine and bovine oviducts

The ultrastructure of oviduct epithelium of clinically healthy cows and 15 sows was investigated using scanning and transmission electron microscopy. In all parts of the oviduct, ciliated and non-ciliated epithelial cells are present, but their number varies in both the investigated animals in different regions of the oviduct, depending on the phase of the estrous cycle. In addition to ciliated cells with numerous cilia on their luminal surface, so-called pale ciliary cells were found in all parts of the oviduct of cows and sows. The cytoplasm of these cells is electron-lucent, their luminal surface carries few cilia and short microvilli. The apical cytoplasm contains species specific secretory granules, which means that these cells have features characteristic of both secretory and ciliated cells. It is suggested that the pale ciliated and non-ciliated secretory cells are functional stages of the same tubar epithelium cell, and that the transformation between these two cell types is regulated by functional requirements of the organ in different phases of the estrous cycle.     

Scanning electron microscopy of the oviduct of Salamandra salamandra (L.) (Amphibia, Urodela)

The oviduct of non-pregnant females of the ovoviviparous salamander, Salamandra salamandra, was examined using SEM-techniques. In the luminal epithelium polygonal ciliated cells were found along the entire surface of the oviduct, except the uterus, and non-ciliated cells with a varying number of short or long microvilli. The ciliated cells occur in the most anterior portion of the oviduct, the pars recta; they are sparsely distributed in the p. convoluta I, but abundant in the p. convoluta II and III. Non-ciliated cells comprise several small gland cells, restricted to the p. convoluta I, II, III, and undifferentiated cells both provided with microvilli, but difficult to be discerned from their surface appearance. The p. convoluta I, II, III is characterized by three types of secretory cells forming tubular glands, each type confined to a given zone. The secretory cells have slender microvilli at their surfaces. In freeze-cracked glands details of their secretory products can be visualized. The findings are compared to previously published TEM-investigations and discussed with regard to some functions of the oviduct during reproduction.     

The Wheel Organ and Hatschek's Groove in the Lancelet,Branchiostoma lanceolatum (Cephalochordata)

The wheel organ is a specialized epithelium in the roof and sides of the adult lancelet oral cavity. It borders the oral epithelium proper, separated by a thin strip of margin cells which are not ciliated but contain a few large dense-cored vesicles apically. The wheel organ cells are tall and strongly ciliated and have dark, heterochromatin-rich nuclei. Dorsally, and slightly paramedially, the organ is further specialized, forming the so-called Hatschek's groove (pit), which consists of two ciliated cell types. The first type synthesizes a dense granular material, the granules being approximately 95 nm in diameter. This is stored basally and apparently it is also released through the basal cell membrane into the blood cavities. The cells at the bottom of Hatschek's groove have peculiar rod-shaped apical cellular regions. Each cell bears one tall cilium surrounded by microvilli and it is apparently involved in the production of secretory material into the groove. It is evident that the histology, and probably also the function, of the wheel organ and its groove is much more complex than hitherto believed.     

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.     

The role of the oviduct and extracellular vesicles during early embryo development in bovine

The oviduct is an important reproductive structure that connects the ovary to the uterus and takes place to important events such as oocyte final maturation, fertilization and early embryonic development. Thus, gametes and embryo can be directly influenced by the oviductal microenvironment composed by epithelial cells such secretory and ciliated cells and oviductal fluid. The oviduct composition is anatomically dynamic and is under ovarian hormones control. The oviductal fluid provides protection, nourishment and transport to gametes and embryo and allows interaction to oviductal epithelial cells. All these functions together allows the oviduct to provides the ideal environment to the early reproductive events. Extracellular vesicles (EVs) are biological nanoparticles that mediates cell communication and are present at oviductal fluid and plays an important role in gametes/embryo - oviductal cells communication. This review will present the ability of the oviducts based on its dynamic and systemic changes during reproductive events, as well as the contribution of EVs in this process.     

Olfactory metamorphosis in the Coastal Giant Salamander (Dicamptodon tenebrosus)

This study examined the gross morphology and ultrastructure of the olfactory organ of larvae, neotenic adults, and terrestrial adults of the Coastal Giant Salamander (Dicamptodon tenebrosus). The olfactory organ of all aquatic animals (larvae and neotenes) is similar in structure, forming a tube extending from the external naris to the choana. A nonsensory vestibule leads into the main olfactory cavity. The epithelium of the main olfactory cavity is thrown into a series of transverse valleys and ridges, with at least six dorsal and nine ventral valleys lined with olfactory epithelium, and separated by ridges of respiratory epithelium. The ridges enlarge with growth, forming large flaps extending into the lumen in neotenes. The vomeronasal organ is a diverticulum off the ventrolateral side of the main olfactory cavity. In terrestrial animals, by contrast, the vestibule has been lost. The main olfactory cavity has become much broader and dorsoventrally compressed. The prominent transverse ridges are lost, although small diagonal ridges of respiratory epithelium are found in the lateral region of the ventral olfactory epithelium. The posterior and posteromedial wall of the main olfactory cavity is composed of respiratory epithelium, in contrast to the olfactory epithelium found here in aquatic forms. The vomeronasal organ remains similar to that in large larvae, but is now connected to the mouth by a groove that extends back through the choana onto the palate. Bowman's glands are present in the main olfactory cavity at all stages, but are most abundant and best developed in terrestrial adults. They are lacking in the lateral olfactory epithelium of the main olfactory cavity. At the ultrastructural level, in aquatic animals receptor cells of the main olfactory cavity can have cilia, short microvilli, a mix of the two, or long microvilli. Supporting cells are of two types: secretory supporting cells with small, electron-dense secretory granules, and ciliated supporting cells. Receptor cells of the vomeronasal organ are exclusively microvillar, but supporting cells are secretory or ciliated, as in the main olfactory cavity. After metamorphosis two distinct types of sensory epithelium occur in the main olfactory cavity. The predominant epithelium, covering most of the roof and the medial part of the floor, is characterized by supporting cells with large, electron-lucent vesicles. The epithelium on the lateral floor of the main olfactory cavity, by contrast, resembles that of aquatic animals. Both types have both microvillar and ciliated receptor cells. No important changes are noted in cell types of the vomeronasal organ after metamorphosis. A literature survey suggests that some features of the metamorphic changes described here are characteristic of all salamanders, while others appear unique to D. tenebrosus.     

Fine Structure of Tentacles,Arms and Associated Coelomic Structures of Cephalodiscus gracilis (Pterobranchia,Hemichordata)

The tentacles of the pterobranch Cephalodiscus, a hemisessile ciliary feeder, originate from the lateral aspects of the arms and are covered by an innervated epithelium, the majority of its cells bearing microvilli. Each side of a tentacle has two rows of ciliated cells and additional glandular cells. The coelomic spaces in the tentacles are lined by cross-striated myoepithelial cells, allowing rapid movements of the tentacles. One, possibly two, blood vessels accompany the coelomic canal. On their outer sides the arms are covered by a simple ciliated epithelium with intra-epithelial nerve fibres; the inner side is covered by vacuolar cells. On both sides different types of exocrine cells occur. The collar canals of the mesocoel are of complicated structure. Ventrally their epithelium is pseudostratified and ciliated; dorsally it is lower and forms a fold with specialized cross-striated myoepithelial cells of the coelomic lining. Arms, tentacles, associated coelomic spaces and the collar canal of the mesocoel are considered to be functionally interrelated. It is assumed that rapid regulation of the pore width is possible and even necessary when the tentacular apparatus is retracted, which presumably leads to an increase of hydrostatic pressure in the coelom.     

Olfactory metamorphosis in the coastal tailed frog Ascaphus truei (Amphibia,Anura, Leiopelmatidae)

The structure of the olfactory organ in larvae and adults of the basal anuran Ascaphus truei was examined using light micrography, electron micrography, and resin casts of the nasal cavity. The larval olfactory organ consists of nonsensory anterior and posterior nasal tubes connected to a large, main olfactory cavity containing olfactory epithelium; the vomeronasal organ is a ventrolateral diverticulum of this cavity. A small patch of olfactory epithelium (the “epithelial band”) also is present in the preoral buccal cavity, anterolateral to the choana. The main olfactory epithelium and epithelial band have both microvillar and ciliated receptor cells, and both microvillar and ciliated supporting cells. The epithelial band also contains secretory ciliated supporting cells. The vomeronasal epithelium contains only microvillar receptor cells. After metamorphosis, the adult olfactory organ is divided into the three typical anuran olfactory chambers: the principal, middle, and inferior cavities. The anterior part of the principal cavity contains a “larval type” epithelium that has both microvillar and ciliated receptor cells and both microvillar and ciliated supporting cells, whereas the posterior part is lined with an “adult‐type” epithelium that has only ciliated receptor cells and microvillar supporting cells. The middle cavity is nonsensory. The vomeronasal epithelium of the inferior cavity resembles that of larvae but is distinguished by a novel type of microvillar cell. The presence of two distinct types of olfactory epithelium in the principal cavity of adult A. truei is unique among previously described anuran olfactory organs. A comparative review suggests that the anterior olfactory epithelium is homologous with the “recessus olfactorius” of other anurans and with the accessory nasal cavity of pipids and functions to detect water‐borne odorants. J. Morphol. 2011. © 2011 Wiley Periodicals, Inc.     

Transitional epithelial zone of the bovine nasal mucosa

To determine the extent and ultrastructure of epithelium lining the transitional nasal mucosa of the neonate, gnotobiotic calf tissues were prepared for scanning and transmission electron microscopy. Stratified cuboid epithelium of the rostral 40% of the nasal cavity contained few ciliated cells; the next caudal 10-15%, although ciliated, had extensive nonciliated areas. The predominant type of surface cell was nonciliated, had short microvilli, and contained a multilobate nucleus and numerous pinocytotic vesicles. In some areas the surface of these cells presented a cobblestone appearance. Basal cells contained numerous bundles of filaments, ribosomes, and basal vesicles. Caudally, nonciliated columnar cells included a cell type similar to the more rostral cuboid cell, as well as brush cells and immature secretory and ciliated cells. Goblet cells were infrequently observed. Intraepithelial nerve terminals were abundant. Other intraepithelial cells, often difficult to identify owing to varying characteristics, included lymphocytes. Based upon comparisons of this neonatal epithelium with mature epithelium, observed in earlier studies of other mammalian species, the transitional mucosa is believed normally to occupy an extensive area of the nasal cavity.     

Evolutionary conservation of an epitope associated with striated rootlets in different epithelial ciliated cells.

In ciliated cells of metazoa, striated rootlets associated with basal bodies anchor the ciliary apparatus to the cytoskeleton. We have used here a monoclonal antibody against a 175 kDa protein associated with the striated rootlets of quail ciliated cells, to study ciliated cells of different species. In mussel gill epithelium the antibody recognized a protein of 92 kDa which shows a periodic distribution along the striated rootlets. In frog ciliated palate epithelium, two different rootlets are associated with basal bodies, both are decorated and only one protein of 48 kDa is recognized on immunoblot. The antigen is arranged in a helix around the striated rootlets. In rabbit ciliated oviduct epithelium, we detected the presence of very small and thin rootlets which are weakly labeled. We have shown that an epitope associated with the striated rootlets is preserved through evolution although the molecular weight of the peptide varies. We have also observed the appearance of this epitope on protein associated with junctional complexes in rabbit and cytoskeleton component in quail oviduct.     

The postbranchial digestive tract of the ascidian, Polyandrocarpa misakiensis (Tunicata: Ascidiacea). 2. Stomach

The organization of the stomach in the compound styelid ascidian, Polyandrocarpa misakiensis, is described, and the morphology and cell types of the stomach is discussed from the phylogenetic viewpoint. The stomach is a sac-like organ whose wall is formed into longitudinal folds. The stomach consists of external and internal epithelium. The internal epithelium is simple columnar, except for the bottom of the folds. There are five cell types: absorptive cells, zymogenic cells, endocrine cells, ciliated mucous cells, and undifferentiated cells. The absorptive cells have numerous microvilli. The apical region of these cells is occupied by coated vesicles. The zymogenic cells have a conical outline and a few microvilli on their apical surfaces. There are secretory granules in the apical region of zymogenic cells. The endocrine cells have low cell height and electron-dense granules around the nucleus. Endocrine cells have one or two cilia and a few microvilli on the apical surfaces. The basolateral part of these cells often bulges into the adjoining cells. Immunoelectron microscopy revealed that some endocrine cells have serotonin-like immunoreactivity. The ciliated mucous cells are restricted to a single ventral groove. They have numerous microvilli and a few cilia on their apical surfaces. Moderately electron-dense granules are accumulated in the apical part of the ciliated mucous cells. Undifferentiated cells, filled with free ribosomes, form a pseudostratified epithelium in the base of each fold. The nucleus of undifferentiated cells has a prominent nucleolus. The pseudostratified epithelium of the pyloric caecum consists of electron-dense and electron-light cells.     

[Ciliogenesis in the mucous cells of the quail oviduct. I. Ultrastructural study in the laying quail]

The luminal epithelium of the oviduct (magnum) of laying quails is composed of ciliated cells and mucous cells. Ciliogenesis was observed in some of the mucous cells. Both centrioles of the diplosome migrate to the top of the cell, and one of them induces the formation of a rudimentary cilium. In some of the other cells, that are filled with mucous granules, the formation of basal bodies by an acentriolar pathway was observed. In these cells, numerous, dense fibrous masses are associated with the forming face of the Golgi apparatus. In the Golgi zone, generative complexes composed of a deuterosome and some forming procentrioles were found. Cilia develop from completed basal bodies. During ciliogenesis, the Golgi apparatus is disorganized, and generally the production of mucous granules is arrested. The nucleus is also modified: it becomes larger and the chromatin is dispersed. It is assumed that mucous cells are able to be transformed into ciliated cells in the oviduct of laying quails.     

Nonolfactory surface epithelium of the nasal cavity of the bonnet monkey: a morphologic and morphometric study of the transitional and respiratory epithelium

The purpose of the present study was to characterize ultrastructurally the nonolfactory nasal epithelium of a nonhuman primate, the bonnet monkey. Nasal cavities from eight subadult bonnet monkeys were processed for light microscopy, and scanning and transmission electron microscopy. Nonolfactory epithelium covered the majority of the nasal cavity and consisted of squamous (SE), transitional (TE), and respiratory epithelium (RE). Stratified SE covered septal and lateral walls of the nasal vestibule, while ciliated pseudostratified RE covered most of the remaining nasal cavity. Stratified, nonciliated TE was present between SE and RE in the anterior nasal cavity. This epithelium was distinct from the other epithelial populations in abundance and types of cells present. TE was composed of lumenal nonciliated cuboidal cells, goblet cells, small mucous granule (SMG) cells, and basal cells, while RE contained ciliated cells, goblet cells, SMG cells, basal cells, and cells with intracytoplasmic lumina lined by cilia and microvilli. TE and RE contained similar numbers of total epithelial cells and basal cells per millimeter of basal lamina. TE was composed of more SMG cells but fewer goblet cells compared to RE. We conclude that nonolfactory nasal epithelium in the bonnet monkey is complex with distinct regional epithelial populations which must be recognized before pathologic changes within this tissue can be assessed adequately.     

Sperm storage and spermatozoa interaction with epithelial cells in oviduct of Chinese soft‐shelled turtle,Pelodiscus sinensis

Spermatozoa are known to be stored within the female genital tract after mating in various species to optimize timing of reproductive events such as copulation, fertilization, and ovulation. The mechanism supporting long‐term sperm storage is still unclear in turtles. The aim of this study was to investigate the interaction between the spermatozoa and oviduct in Chinese soft‐shelled turtle by light and electron microscopy to reveal the potential cytological mechanism of long‐term sperm storage. Spermatozoa were stored in isthmus, uterine, and vagina of the oviduct throughout the year, indicating long‐term sperm storage in vivo. Sperm heads were always embedded among the cilia and even intercalated into the apical hollowness of the ciliated cells in the oviduct mucosal epithelium. The stored spermatozoa could also gather in the gland conduit. There was no lysosome distribution around the hollowness of the ciliated cell, suggesting that the ciliated cells of the oviduct can support the spermatozoa instead of phagocytosing them in the oviduct. Immune cells were sparse in the epithelium and lamina propria of oviduct, although few were found inside the blood vessel of mucosa, which may be an indication of immune tolerance during sperm storage in the oviduct of the soft‐shelled turtle. These characteristics developed in the turtle benefited spermatozoa survival for a long time as extraneous cells in the oviduct of this species. These findings would help to improve the understanding of reproductive regularity and develop strategies of species conservation in the turtle. The Chinese soft‐shelled turtle may be a potential model for uncovering the mechanism behind the sperm storage phenomenon.     

Surface area of apical and basolateral plasmalemma of epithelial cells of the ductuli efferentes testis of the rat

Serial sectioning was used to determine the occurrence of ciliated cells, and a morphological technique was used to estimate the relative and absolute surface areas of apical and basolateral membrane of the epithelial cells lining the ductuli efferentes of the rat. It was found that the ciliated cells constitute 15% of the epithelial cells and occur as groups of mainly 1–3 cells which are distributed at random in the duct epithelium. For the non-ciliated cells it was estimated that the formation of microvilli by the apical membrane increased the surface area of that border by a factor of 37-fold. The average surface density of the basolateral membrane was 76% the surface density of the apical membrane. However, there was a 3-fold increase in surface density along the apicalbasal axis of the basolateral plasmalemma. In the Discussion, the ductuli efferentes are compared to their homologue, the proximal tubules of the kidney, in the rates of fluid transport and membrane adaptations of their epithelium.     

[Ciliogenesis in the mucous cells of the quail oviduct. II. Hormonal control]

The hormonal control of ciliogenesis and transformation of mucous cells was studied in the oviduct (magnum) of ovariectomized quails. Estradiol benzoate induces ciliogenesis with doses varying from 10 mug/day to 100 mug/day after 6 days of treatment. With 100 mug/day, differentiation of some mucous cells is also induced as well as the formation of transitory "mixed cells" which are in the process of ciliogenesis and contain mucous granules. Associated with progesterone (1 mg/day), estradiol benzoate (10 mug/day) induces the differentiation of mucous cells and ciliated cells. The luminal epithelium of quails injected with this mixture is similar to the luminal epithelium observed in the oviduct of laying quails. With the same dose of progesterone (1 mg/day) and 20 mug/day of estradiol benzoate for 6 days, ciliogenesis is completely inhibited. All epithelial cells are secretory cells. Transformation of 50% of the mucous cells into ciliated cells is obtained by following the previous estradiol-progesterone treatment with the injection of estradiol benzoate (20 mug/day) for 3 days. Divisions of mucous cells were also observed. It is also possible to induce ciliogenesis in some mucous cells by withdrawing both hormones for 3 days. In this case, no cell divisions were observed.     

Sperm storage and degradation in the ovary of a marine copulating sculpin,Alcichthys alcicornis (Teleostei: Scorpaeniformes): Role of intercellular junctions between inner ovarian epithelial cells

The morphology of female sperm storage during the spawning period and the morphology of sperm degradation after the spawning period were investigated by electron microscopy in a copulating teleost, Alcichthys alcicornis. The spermatozoa were maintained in the ovarian cavity, floating in the ovarian fluid during the spawning period. The spermatozoa then degenerated and were phagocytized by macrophages invading the ovarian cavity after the spawning period. In the ovary during the spawning period, horseradish peroxidase used as a tracer revealed tight junctional complexes connecting adjacent cells of the inner ovarian epithelia (ovarian wall epithelium and ovigerous lamella epithelium). This indicates that a compartmentalization of the ovarian cavity occurs during the spawning period. The junctional complexes were breached after the spawning period, as shown by the fact that horseradish peroxidase penetrated the ovarian cavity via the intercellular space between the adjoining ovigerous lamella epithelia. These results suggest that the spermatozoa in the ovarian cavity are isolated from the maternal immune system by the tight junctional complexes between the adjoining inner ovarian epithelia during the spawning period, and then are eliminated by immune cells following the breakdown of the junctional complexes after the spawning period. J. Morphol. 233:153–163, 1997. © 1997 Wiley-Liss, Inc.     

A scanning electron microscopic study of the luteo-follicular complex. II. Events leading to ovulation.

Morphological changes on the ovarian surface of different mammals both before and during ovulation have been examined by scanning electron microscopy. Preovulatory follicles were blisterlike structures that protruded markedly from the ovarian surface. Basal areas of preovulatory follicles were covered with polyhedral cells containing numerous microvilli, whereas on the lateral surfaces, superficial cells were elongated and possessed few microvilli. At the apex of the follicle, cells were very flattened and possessed few microvilli, which were present only in regions of intercellular contact. In some apical areas, cells appeared to be degenerating, whereas in other regions, groups of cells had "sloughed off." In addition, a fluidlike material was observed to exude from intercellular spaces of the superficial epithelium and to cover some apical cells. By transmission electron microscopy, the same fluidlike material was observed to (1) infiltrate the connective tissue of the tunica albuginea, (2) accumulate under the basal lamina, and (3) distend intercellular spaces of the superficial epithelium. Just prior to ovulation, large, irregular areas of the apex were ruptured and the oocyte, covered with a large amount of fluid, appeared to emerge from the follicle. At ovulation, the oocyte was not completely covered with follicle cells and the zona pellucida was clearly evident. The surface of the zona was quite irregular and contained numerous infoldings, channels and crypts. Follicle cells had polyhedral or star shapes and possessed large cytoplasmic evaginations that obliquely penetrated the zona. Both the zona pellucida and corona cells were covered with a fine layer of granular material. The SEM results and parallel TEM observations suggest that a local increase of fluids (edema) may be an important factor in the final decomposition of the distended and weakened apex of the preovulatory follicle. In addition, the participation of follicle cells, smooth muscle cells and the oviduct in the escape of the oocyte from the ruptured follicle is discussed.     

An ultrastructural study of the dorsal lingual epithelium of the crab-eating frog,Rana cancrivora

The amphibian tongue contains two types of papilla which are believed to function in gustation and in the secretion of salivary fluid. Scanning electron microscopy reveals that columnar, filiform papillae are compactly distributed over nearly the entire dorsal surface of the tongue of the frog, Rana cancrivora, and fungiform papillae are scattered among the filiform papillae. Microridges and microvilli are distributed on the epithelial cell surface of the extensive area of the filiform papillae. Light microscopy shows that the apex of each filiform papilla is composed of stratified columnar and/or cuboidal epithelium and its base is composed of simple columnar epithelium. Transmission electron microscopy reveals that most of the epithelium of the filiform papillae is composed of cells that contain numerous round electron-dense granules 1–3 μm in diameter. Cellular interdigitation is well developed between adjacent cells. On the free-surface of epithelial cells, microridges or microvilli are frequently seen. Between these granular cells, a small number of ciliated cells, mitochondria-rich cells and electron-lucent cells are inserted. In some cases, electron-dense granules are present in the ciliated cells. At higher magnification, the electron-dense granules appear to be covered with patterns of spots and tubules. Overall, the morphology and ultrastructure of the lingual epithelium of the three species of Rana that have been studied are quite similar, but they can be easily distinguished from those of Bufo japonicus. Therefore, it appears that lingual morphology is phylogenetically constrained among members of the predominantly freshwater genus Rana to produce uniformity of papillary structure and this morphology persists in Rana cancrivora despite the distinct saline environment in which it lives. © 1993 Wiley-Liss, Inc.