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.     

Electron microscopic studies on the pineal organ of the antarctic penguin, (Pygoscelis papua)

The pineal organ of the migratory antarctic penguin, Pygoscelis papua, has a lobular structure. Clusters formed by different types of parenchymal cells are separated by connective tissue septa containing blood vessels. The predominant cell type displays a well-developed Golgi complex, free ribosomes, clear and granular vesicles (secretory granules), and lysosomes. Other cell types found in the gland are supporting and ependymal-like cells. The former contain dense bodies and filament bundles, the latter possess abundant cilia and clusters of ribosomes. Typical photoreceptor elements are lacking. Blood vessels are located within a perivascular space bordered by basal laminae. This perivascular space extends between the basal protrusions of the parenchymal cells. The presence of pinocytotic vesicles, secretory granules and cytoplasmic processes in the vicinity of these spaces suggests active sites of transport and exchange of substances. Intercellular conaliculi-like spaces are surrounded by parenchymal cells rich in microvilli. These cancliculi are continuous with the cavities (invaginations) of secretory and other parenchymal cells.     

Exocytosis of cortical granules from activated oocytes of the toad,Bufo arenarum

Summary Observation of the cortical region of oocytes of Bufo arenarum by transmission electron microscopy reveals modifications on their surface and in the contents of the cortical granules (CG) during activation. In non-activated oocytes only amorphous cortical granules (ACG) can be observed. Activated oocytes display ACG, intermediate cortical granules containing both amorphous and membranous material (ICG), and a third type containing only membranous material (MCG). During exocytosis, CG release their contents into the perivitelline space, where the amorphous and membranous materials are found. The three types of CG found during oocyte activation suggest transformation of ACG to MCG and indicate that the different components of the cortical granules, when released into the perivitelline space, might play different roles in prevention of polyspermy.Members of the Scientific Research Career of CONICET, R. Argentina.     

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.     

Structure of the female reproductive tract of the apple snail. II. Scanning electron microscopy

The albumen gland of Pomacea paludosa, a prosobranch gastropod, contains two main ducts. The albumen gland duct consists of a single layer of secretory and non-secretory cells. The surface of the non-secretory cells is covered with cilia. Microvilli are associated with the luminal edges of the secretory cells. Globules of secretory products appear at the cell surfaces. The capsule gland duct coils through the albumen gland and is composed of two opposing faces each of two layers of cells. The upper layer consists of ciliated non-secretory cells and the microvilli covered necks of the goblet-shaped secretory cells. The bases of the secretory cells comprises the lower layer of cells. Differences in the arrangement of cellular processes and number exists between the duct epithelia.     

Ultrastructure of the human submandibular salivary glands]

By means of electron microscopy cells in the human submandibular glands were studied. It was demonstrated that in acini two types of glandular cells were present: mucosal and seromucosal. In the latter, secretory granules are descrete with electron opaque cores in most of them. Mucocytes are filled with an electron transparent secrete; secretory granules often confluent and their membranes rupture. The acini are surrounded with myoepithelial cells. Intercalated ducts consist of cells with moderately electron opaque granules. In some granules there are dense bodies excentrically situated. In these cells there occur lipid inclusions. Striated ducts are composed of basal (electron transparent) and high cylindric (light and dark) cells. The cylindrical cells have a large amount of mitochondria, deep folds in their basal plasmolemma protruding into cytoplasma. Most of the cells in these parts contain small apically accumulated secretory granules with a dense matrix and separate larger ones scattered in the cell. It is possible to suggest that some secretory granules of ductal or, perhaps, acinar origin contain hormonal products.     

Effect of infection with Trichobilharzia ocellata and Schistosoma mansoni on the ultrastructure of the albumen gland of their respective hosts, Lymnaea stagnalis and Biomphalaria glabrata

The albumen gland, a female accessory sex gland of pulmonate snails, produces the perivitelline fluid. The ultrastructure of the albumen glands of control and infected specimens of Lymnaea stagnalis and Biomphalaria glabrata was studied. The albumen gland of L. stagnalis contains two types of secretory cells--light (active) and dark (inactive)--and two types of supporting cells--centroacinar and myoepithelial. The secretory cells apparently represent two activity stages of one type of cell. The gland B. glabrata possesses only one secretory cell type, which alternates with one type of supporting cell. The albumen glands of L. stagnalis and B. glabrata infected at a juvenile stage were studied 4 and 14 weeks (L. stagnalis) and 4 and 9 weeks (B. glabrata) after exposure. After four weeks' infection, B. glabrata produced some egg masses, but in subsequent stages egg mass production completely coased. Infected L. stagnalis never produced eggs. B. glabrata was apparently infected at a "physiologically" more mature stage than L. stagnalis. The morphology of the albumen glands four weeks after exposure (the daughter sporocyst stage) is in agreement with this hypothesis. At this interval the secretory cells of L. stagnalis appeared to be much more severely affected (inactive Golgi bodies and rough endoplasmic reticulum, crinophagy of the secretory granules) than the cells of B. glabrata. In the later stages studied (shedding of the cercariae), the glands of both species appeared to be completely inactive (reduced height of the epithelium, inactive organelles, crinophagy, absence of secretory granules). At this stage of infection, daughter sporocysts containing cercaria embryos were seen in the connective tissue of the albumen gland of B. glabrata, but not of L. stagnalis. The results thus indicate that the development and synthetic activity of the albumen gland are seriously affected by infection. These processes are known to be under the endocrine control of the female gonadotrophic hormones. Since it has been established that these hormones are normally present in the haemolymph of infected snails, the findings can be explained by assuming that the parasite interferes in some way or other with the snail's endocrine system.     

The postbranchial digestive tract of the ascidian, Polyandrocarpa misakiensis (Tunicata: Ascidiacea). 1. Oesophagus

The organization of the oesophagus in the budding styelid ascidian, Polyandrocarpa misakiensis, is described. The oesophagus consists of external and internal epithelium, and there are loose connective tissue, blood sinuses, and a muscular layer between them. The internal epithelium is simple columnar, except for the bottom of three folds. The external epithelium is simple squamous. The internal epithelium contains four cell types, i.e., ciliated mucous cells, band cells, endocrine cells, and undifferentiated cells. The ciliated mucous cells have apical cilia and microvilli, and two types of mucous vesicle. The band cells also have apical cilia and electron-dense granules in the apical cytoplasm. The endocrine cells are bottle-shaped, and have electron-dense granules both above and below the nucleus. The undifferentiated cells form pseudostratified epithelium at the bottom of each fold, and they have nuclei with prominent nucleoli. One type of coelomic cell, which has retractile cytoplasm, often migrates in the internal epithelium. Near the stomach, there are many darkly stained round cells clustered around the posterior end of the oesophagus. These two types of coelomic cells may be involved in the defense mechanism against the invasion of foreign organisms. The basic organization of the oesophagus of P. misakiensis is similar to those of other ascidians. However, the presence of three folds is a characteristic of a solitary species, rather than of a colonial species. Although ascidians are chordate invertebrates, the organization of their oesophagus is not very complex, which might reflect their life style.     

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.     

Effects of pimozide on the ultrastructure of the pars intermedia in the rat

Summary The effects of pimozide, a dopamine receptor-blocking agent, were studied in the pars intermedia of the rat. The animals received 100 g/100 g pimozide daily for 2, 5, 10, 15, and 20 days. Pimozide induces ultrastructural changes after 5 days of treatment. About 50% of the MSH-cells display characteristics of stimulation. Their cytoplasm is partially or totally depleted of secretory granules. The rough endoplasmic reticulum displays a network of interconnecting cisternae and ribbon-like structures. The well-developed Golgi complexes exhibit numerous dilatations of their cisternae, which contain electron-dense material. The nerve endings are not altered. Twenty days after treatment, the above-described changes have not decreased in magnitude. The present findings suggest that pimozide stimulates the mechanism of synthesis and release in some MSH-cells, most probably the elements underlying an inhibitory dopaminergic control.Supported by CONICET and CIUNC of ArgentinaMember of the Research Career of CONICET, ArgentinaFellow of CONICET, Argentina     

Changes occurring in the epithelium covering the bronchus-associated lymphoid tissue of rats after intratracheal challenge with horseradish peroxidase

Summary Changes occurring in the epithelium covering bronchus-associated lymphoid tissue (BALT) in the rat after several intratracheal administrations of horseradish peroxidase (HRP) were studied using morphological and ultrastructural methods. The epithelium is invaded by W3/ 25-positive (T-helper) lymphocytes, the BALT epithelial cells become Ia-positive and develop microvilli; there is an apparent loss of cilia. The number of non-ciliated cells in stimulated BALT increases. The non-ciliated cells can be subdivided into two cell types, one with electron-dense cytoplasm and cytoplasmic granules and the other without granules. The electron-density of the latter cell type is intermediate between that of the ciliated cells and that of the granulecontaining non-ciliated cells. The granule-containing cell types may be responsible for the uptake of antigens, while the other non-ciliated cell may be involved in the production of the secretory component and the passage of secretory IgA.Supported by a research grant from the Nederlands Astma Fonds     

Fine structure of the excretory system of the deep posterior (Ebner's) salivary glands of the human tongue

Human deep posterior lingual glands (von Ebner's glands) are located beneath the circumvallate papillae. They are formed by tubuloalveolar adenomeres, intercalated ducts and excretory ducts coming together in the main excretory duct. The tubuloalveolar cells, pyramid-shaped, show large and dense secretory granules (clear cored) throughout the cytoplasm, rare basal folds and packed cisternae of rough endoplasmic reticulum (RER) at the basal pole. The columnar cells of the intercalated ducts are arranged in a monolayer. They are characterized by dense, clear-core secretory granules (mostly in the apical cytoplasm), a basal nucleus, well-developed RER and Golgi apparatus, and thin filaments distributed in supra- and perinuclear cytoplasm. Striated ducts are absent. Excretory ducts, coming together in the main duct, are lined by a bistratified epithelium. The inner layer consists of columnar cells showing bundles of tonofilaments with scarce secretory activity. The outer layer is composed of basal cells lying on the basal lamina. The main excretory duct, which opens at the bottom of the vallum, shows a stratified epithelium. The outer side is composed of 2-3 layers of malpighian cells lying on the basal lamina. The inner side consists of a single layer of cuboidal-columnar cells with dense apical granules and well-developed organelles synthesizing and condensing secretions. These cells interpolate with goblet cells, rare mitochondria-rich cells, ciliated cells and numerous small globous cells showing a clear matrix and lacking secretory granules. The cilia show a 9 + 2 microtubular structure with basal bodies provided with striated rootlets. Myoepithelial cells surround with their processes the basal portions of the secretory cells and the intercalated ducts. The conclusions concern some comparative aspects and some hypothesis on the functional role of goblet cells, ciliated cells and epithelial cells lining the different ducts, also in relation to the final secretory product.     

Morphology and ultrastructure of the venom glands of the northern pacific rattlesnake Crotalus viridis oreganus

The venom gland of Crotalus viridis oreganus is composed of two discrete secretory regions: a small anterior portion, the accessory gland, and a much larger main gland. These two glands are joined by a short primary duct consisting of simple columnar secretory cells and basal horizontal cells. The main gland has at least four morphologically distinct cell types: secretory cells, the dominant cell of the gland, mitochondria-rich cells, horizontal cells, and “dark” cells. Scanning electron microscopy shows that the mitochondria-rich cells are recessed into pits of varying depth; these cells do not secrete. Horizontal cells may serve as secretory stem cells, and “dark” cells may be myoepithelial cells. The accessory gland contains at least six distinct cell types: mucosecretory cells with large mucous granules, mitochondria-rich cells with apical vesicles, mitochondria-rich cells with electron-dense secretory granules, mitochondria-rich cells with numerous cilia, horizontal cells, and “dark” cells. Mitochondria-rich cells with apical vesicles or cilia cover much of the apical surface of mucosecretory cells and these three cell types are found in the anterior distal tubules of the accessory gland. The posterior regions of the accessory gland lack mucosecretory cells and do not appear to secrete. Ciliated cells have not been noted previously in snake venom glands. Release of secretory products (venom) into the lumen of the main gland is by exocytosis of granules and by release of intact membrane-bound vesicles. Following venom extraction, main gland secretory and mitochondria-rich cells increase in height, and protein synthesis (as suggested by rough endoplasmic reticulum proliferation) increases dramatically. No new cell types or alterations in morphology were noted among glands taken from either adult or juvenile snakes, even though the venom of each is quite distinct. In general, the glands of C. v. oreganus share structural similarities with those of crotalids and viperids previously described.     

Some features of the structure and histochemistry of the rat parathyroid gland

Summary Some features of the structure and histochemistry of the rat parathyroid gland have been studied using a variety of histological and histochemical staining methods. The gland is composed of a compact parenchyma consisting essentially of a single cell type. The parenchyma is encapsulated by a connective tissue layer which extends into it and holds abundant branches of blood vessels. In the parenchymal cells four types of protein granules are demonstrated by the tetrazonium, DDD-diazo blue B, alkaline tetrazolium and HNAH-diazo blue B methods respectively. The DDD-diazo blue B reactive granules are considered to relate to the secretory activity of the parenchymal cells in view of their morphology and recent biochemical data on the nature of parathyroid hormone. The cytophysiological significance of the other three types of protein granules was discussed on the basis of their morphological features. Besides protein granules the parenchymal cells contain glycogen, RNA and DNA, and are reactive for alkaline phosphatase. The quantity of these substances and the enzyme activity seem to reflect to a certain extent different states of cellular activity. The parenchymal cells show scanty sudanophilic lipid content in paraffin sections and are devoid of basophilic mucopolysaccharides. Further, the cells are negative for acid phosphatase. In the connective tissue stroma of the gland the vascular endothelial cells show high alkaline phosphatase activity, and a hypothesis is presented as to the physiological significance of this high enzyme activity.     

"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.     

Morphological changes in the oviductal endometrium during the reproductive cycle of the tortoise,Gopherus polyphemus

The oviducts of 24 tortoises (Gopherus polyphemus) were examined using histological techniques and scanning electron microscopy to determine endometrial morphology. Measurements of endometrial characteristics (epithelial cell height, cilia length, thickness of endometrial glandular layer, and glandular diameter) in the uterus and tube (tuba uterina) were obtained to determine changes during the reproductive cycle. Epithelial cell height increases in both the uterus and the tube during vitellogenesis and remains hypertrophied during gravidity. Cilia length increases in the uterus during late vitellogenesis and gravidity, but the length of tubal cilia does not change during the reproductive cycle. The ratio of secretory to ciliated epithelial cells in the oviduct increases from quiescence to gravidity. The thickness of the glandular endometrial layer increases in both the uterus and tube during vitellogenesis. In the uterus, the glandular layer decreases in thickness during gravidity. The diameter of the uterine glands increases throughout vitellogenesis and gravidity; however, following ovulation glandular cells become depleted of secretory granules and cell height diminishes. The diameter of the tubal glands is unchanged during the reproductive cycle. Oviductal hypertrophy during vitellogenesis coincides with elevated circulating estradiol, whereas during gravidity progesterone concentrations peak (Taylor, '82, PhD Dissertation, University of Florida, Gainesville) and may induce secretion of albumen and eggshell components.     

Immuno-electron microscopy of formation,degradation and exocytosis of the ovulation neurohormone in Lymnaea stagnalis

Summary The cerebral caudodorsal cells (CDC) of the pulmonate snail Lymnaea stagnalis are involved in the control of egg laying and associated behaviour by releasing various peptides. One of these is the ovulation hormone (CDCH). The cellular dynamics of this peptide have been studied using an antiserum raised to a synthetic portion of CDCH comprising the 20–36 amino acid sequence. With the secondary antibody-immunogold technique, specific immunoreactivity was found in all CDC. Rough endoplasmic reticulum and Golgi apparatus showed very little reactivity as did secretory granules that were in the process of being budded off from the Golgi apparatus. However, secretory granules that were being discharged from the Golgi apparatus, were strongly reactive. Secretory granules within lysosomal structures revealed various degrees of immunoreactivity, indicating their graded breakdown. Large electrondense granules, formed by the Golgi apparatus and thought to be involved in intracellular degradation of secretory material, were only slightly reactive. In the axon terminals secretory granules released their contents into the haemolymph by the process of exocytosis. The exteriorized contents were in most cases clearly immunopositive.The possibility has been discussed that CDCH is cleaved from its polypeptide precursor within secretory granules during granule discharge from the Golgi apparatus; subsequently, the mature secretory granules would be transported towards the neurohaemal axon terminals where they release CDCH into the haemolymph. Superfluous secretory material would be degraded by the lysosomal system including the large electron-dense granules.     

THE CYTOLOGY OF THE NORMAL PARATHYROID GLANDS OF MAN AND VIRGINIA DEER : A Light and Electron Microscopic Study with Morphologic Evidence of Secretory Activity

The normal parathyroids of six humans and a Virginia deer were studied by light and electron microscopy. The parenchyma of the deer parathyroid is composed of uniform chief cells, which contained 100 to 400 mµ electron-opaque, membrane-limited granules, presumed to be secretory granules, in addition to the usual cytoplasmic organelles. Desmosomes are present between adjacent cells, and rare cilia are observed protruding from the chief cells into the intercellular space. The human parathyroids contain chief cells in two phases—active and inactive—as well as oxyphil cells. Active chief cells have a large Golgi apparatus, sparse glycogen, numerous secretory granules, and rare cilia. Inactive chief cells contain a small Golgi apparatus, abundant glycogen, and few secretory granules. Both forms have the usual cytoplasmic organelles and, between adjacent cells, desmosomes. Oxyphil cell cytoplasm is composed of tightly packed mitochondria and glycogen granules, with rare secretory granules. Cells with cytoplasmic characteristics intermediate between chief and oxyphil cells, possibly representing transitional cells, have been observed. Secretory granules of both man and deer are composed of 100 to 200 A particles and short rods, and the granules develop from prosecretory granules in the Golgi region of the cell. The human secretory granules are smaller and more variable in shape than those of the deer. The granules are iron and chrome alum hematoxylin-positive, argyrophilic, and aldehyde fuchsin-positive, permitting light microscopic identification. They are also found in the capillary endothelial cells of the parathyroid and in its surrounding connective tissue. The secretory granules of the parathyroid cells can thus be followed from their formation in the Golgi apparatus almost to their extrusion into the blood stream.     

Functional morphology of coronal and peristomeal podia in Sphaerechinus granularis (Echinodermata,Echinoida)

Summary Coronal podia of Sphaerechinus granularis are anchoring (adhering) appendages involved in either locomotion or capture of drift materials. Adhesion is not due to the presumed sucker action of the disc but relies entirely on secretions of the disc epidermis. Peristomeal podia function in wrapping together food particles or food fragments in an adhesive material thus facilitating their capture by the Aristotle's lantern. In both types of podia, the disc epidermis is made up of four cell types: non-ciliated secretory cells (NCS cells) that contain graules whose content is at least partly mucopolysaccharidic in nature, ciliated secretory cells (CS cells) containing granules of unknown nature, ciliated non-secretory cells (CNS cells) and support cells. The cilia of CS cells are subeuticular whereas those of CNS cells, although also short and rigid, traverse the cuticle and protrude in the outer medium. All these cells are presumably involved in an adhesive/de-adhesive process functioning as a duogland adhesive system. Adhesive secretion would be produced by NCS cells and de-adhesive secretion by CS cells. These secretions would be controlled through stimulations by the two types of ciliated cells (receptor cells) which presumably interact with the secretory cells by way of the nerve plexus. This model of adhesion/de-adhesion fits well with the activities of both coronal and peristomeal podia. The secretion of NCS cells would make up a bridge of adhesive material between a podium and the substratum (coronal podia) or would coat and gather food particles (peristomeal podia), respectively. The de-adhesive material enclosed in the granules of CS cells would allow the podia (either coronal or peristomeal) to easily become detached from the substratum and to always remain clear of any particles.Research Assistant, National Fund for Scientific Research (Belgium)     

Ultrastructure of the Olfactory Epithelium in the Australian Lungfish Neoceratodus forsteri

Four cell types are present in the olfactory epithelium of Neoceratodus forsteri, i.e., olfactory receptor cells, supporting cells, non-sensory ciliated cells, and basal cells. Only microvilli and no cilia were observed on the receptor cells. The neurotubules pass out into these microvilli. Conspicuous arrays of agranular endoplasmic reticulum are present in the nuclear region of the receptor cells. The supporting cells are provided with microvilli. These cells may be secretory. The non-sensory ciliated cells produce secretory granules containing acid mucopolysaccharides. A discontinuous zonula occludens appears to be present.