Fine structure of the silk gland in the mite Ornithocheyletia sp. (Prostigmata,Cheyletidae)

Silk spinning is widely-spread in trombidiform mites, yet scarse information is available on the morphology of their silk glands. Thus this study describes the fine structure of the prosomal silk glands in a small parasitic mite, Ornithocheyletia sp. (Cheyletidae). These are paired acinous glands incorporated into the podocephalic system, as typical of the order. Combined secretion of the coxal and silk glands is released at the tip of the gnathosoma. Data obtained show Ornithocheyletia silk gland belonging to the class 3 arthropod exocrine gland. Each gland is composed of seven pyramidal secretory cells and one ring-folded intercalary cell, rich in microtubules. The fine structure of the secretory cells points to intensive protein synthesis resulted in the presence of abundant uniform secretory granules. Fibrous content of the granules is always subdivided into several zones of two electron densities. The granules periodically discharge into the acinar cavity by means of exocytosis. The intercalary cell extends from the base of the excretory duct and contributes the wall of the acinar cavity encircling the apical margins of the secretory cells. The distal apical surface of the intercalary cell is covered with a thin cuticle resembling that of the corresponding cells in some acarine and myriapod glands. Axon endings form regular synaptic structures on the body of the intercalary cell implying nerve regulation of the gland activity.     

Morphology of the exocrine glands of the frog skin

Frog skin contains three distinct types of exocrine glands: granular (poison), mucous, and seromucous. The granular gland forms a syncytial secretory compartment within the acinus, which is surrounded by smooth muscle cells. The mucous and seromucous glands are easily identifiable as distinct glands. The serous and mucous secretory cells are arranged in a semilunar configuration opposite the ductal end and are filled with granules. Within the acinus, located at the ductal pole of the gland, are distinct groups of cells with few or no granules in the cytoplasm. In both the mucous and seromucous gland there is a cell type with abundant mitochondria; the one in the mucous gland is located in the region adjacent to the secretory cells. The duct of these glands is two-layered, with the individual cells appearing morphologically similar to the layers of the skin epithelium as the duct traverses the skin. The duct appears to be patent throughout its length. The morphological heterogeneity and distinct distribution of the cell types within the gland acinus may be indicative of a functional heterogeneity that allows the production of distinctly different types of secretion from the same gland type, depending on the type of stimulus.     

Study on pathway and characteristics of ion secretion of salt glands of Limonium bicolor

Recretohalophytes with specialized salt-secreting structures, including salt glands and salt bladders, can secrete excess salts from plant tissues and enhance salinity tolerance of plants. However, the pathway and property of salt secretion by the salt gland has not been elucidated. In the article, Limonium bicolor Kuntze was used to investigate the pathway and characteristics of salt secretion of salt gland. Scanning electron microscope micrographs showed that each of the secretory cells had a pore in the center of the cuticle, and the rice grain-like secretions were observed above the pore. The chemical composition of secretions from secretory pores was mainly NaCl using environmental scanning electron microscope technique. Non-invasive micro-test technology was used to directly measure ion secretion rate of salt gland, and secretion rates of Na⁺ and Cl^? were greatly enhanced by a 200-mmol/L NaCl treatment. However, epidermal cells and stoma showed little secretion of ions. In conclusion, our results provide evidence that the salt glands of L. bicolor have four secretory pores and that NaCl is secreted through these pores of salt gland.     

Fine structure of the axillary gland in the brown bullhead (Ictalurus nebulosus)

The axillary glands of Ictalurus are lobulated invaginations of the epidermis, opening at a pore between the pectoral spine and the cleithrum. Holocrine cells lining a false lumen form a viscous secretion. The secretory cells originate in the tenuous basal layer of the gland wall. Secretion is initiated by the formation of compound vesicles in cells that become very large and have complex cytoplasm of a varied appearance. Golgi systems are well developed and the perinuclear cytoplasm may contain many mitochondria and sacs of ribosomal endoplasmic reticulum; some tracts of cytoplasm are vesicular and contain free ribosomes. Some cells contain numerous large lysosomes, and some have extensive contents of fibrillar masses imperfectly separated by membranes, that recall the appearance of the mucous secretion of goblet cells. The secretory cells break down, releasing the degenerating organelles, including the nuclei, into the false lumen. Some structures are still recognizable in the secretion even after it has been expelled, but the main part of the formed secretion consists of the mucus-like masses. Various leucocytes are found in the gland walls and embedded in the secretion. The fine structure differentiates the holocrine cells of the axillary gland from the club cells of the epidermis, and from the venom glands associated with the fin spines of catfishes. The function of the axillary gland secretion remains unknown.     

The ultrastructure and histology of the perinotal epidermis and defensive glands of two species of Onchidella (Gastropoda: Pulmonata)

Histology and electron microscopy were used to describe and compare the structure of the perinotal epidermis and defensive glands of two species of shell-less marine Systellommatophora, Onchidella capensis and Onchidella hildae (Onchidiidae). The notum of both species is composed of a layer of epithelial and goblet cells covered by a multi-layered cuticle. Large perinotal multi-cellular glands, that produce thick white sticky mucus when irritated, are located within the sub-epidermal tissue. The glands are composed of several types of large secretory cell filled with products that stain for acidic, sulphated and neutral mucins, and some irregularly shaped support cells that surround a central lumen. The products of the secretory cells are produced by organelles that are basal in position. The entire gland is surrounded by a well-developed capsule of smooth muscle and collagen, and in addition smooth muscle surrounds the cells within the glands. Based on the size of the gland cells, their staining properties, and the appearance of their stored secretions at the transmission electron microscope level, five different types of secretory cells were identified in O. capensis and four in O. hildae. The products of these cells, which are released by holocrine secretion, presumably mix in the lumen of the duct as they are forced out by contraction of the smooth muscle. The structural similarity of these glands to those of siphonariids, suggest that they have a common ancestry.     

Structure of the male reproductive accessory glands of Pterostichus nigrita (Coleoptera: Carabidae), their role in spermatophore formation

Accessory gland secretions of male insects have many important functions including the formation of spermatophores. We used light and electron microscopy to investigate the structure of the accessory glands and posterior vasa deferentia of the carabid beetle Pterostichus nigrita to try to determine where spermatophore material is produced. Each accessory gland and posterior vas deferens had an outer layer of longitudinal muscle, beneath which was a layer of connective tissue and a thin band of circular muscle, all of which surrounded a layer of epithelial cells lining the lumen of the ducts. Based on the ultrastructure of the epithelial cells, and their secretory products, we identified two epithelial cell types in each region (distal and proximal) of the accessory glands and four types in the posterior vas deferens. Most secretory products, which stained positively for proteins and some mucins, were released into the lumen of the ducts by apocrine secretion. The accessory glands produced one type of secretory product whereas in posterior vasa deferentia, four types of secretory products were found layered in the lumen. Our results suggest that most of the structural material used to construct a spermatophore is produced by the cells of the posterior vasa deferentia.     

Ultrastructure of the male reproductive accessory glands in the medfly Ceratitis capitata (Diptera: Tephritidae) and preliminary characterization of their secretions

The morphology and the ultrastructure of the male accessory glands and ejaculatory duct of Ceratitis capitata were investigated. There are two types of glands in the reproductive apparatus. The first is a pair of long, mesoderm-derived tubules with binucleate, microvillate secretory cells, which contain smooth endoplasmic reticulum and, in the sexually mature males, enlarged polymorphic mitochondria. The narrow lumen of the gland is filled with dense or sometimes granulated secretion, containing lipids. The second type consists of short ectoderm-derived glands, finger-like or claviform shaped. Despite the different shape of these glands, after a cycle of maturation, their epithelial cells share a large subcuticular cavity filled with electron-transparent secretion. The ejaculatory duct, lined by cuticle, has epithelial cells with a limited involvement in secretory activity. Electrophoretic analysis of accessory gland secretion reveals different protein profiles for long tubular and short glands with bands of 16 and 10 kDa in both types of glands. We demonstrate that a large amount of accessory gland secretion is depleted from the glands after 30 min of copulation.     

ULTRASTRUCTURAL DEVELOPMENT OF CAPITATE GLANDULAR HAIRS OF CANNABIS SATIVA L. (CANNABACEAE)

The capitate-sessile and capitate-stalked glands of the glandular secretory system in Cannabis, which are interpreted as lipophilic type glandular hairs, were studied from floral bracts of pistillate plants. These glands develop a flattened multicellular disc of secretory cells, which with the extruded secretory product forms the gland head and the auxiliary cells which support the gland head. The secretory product accumulates beneath a sheath derived from separation of the outer wall surface of the cellular disc. The ultrastructure of secretory cells in pre-secretory stages is characterized by a dense ground plasm, transitory lipid bodies and fibrillar material, and well developed endoplasmic reticulum. Dictyosomes and dictyosome-derived secretory vesicles are present, but never abundant. Secretory stages of gland development are characterized by abundant mitochondria and leucoplasts and by a large vacuolar system. Production of the secretory product is associated with plastids which increase in number and structural complexity. The plastids develop a paracrystalline body which nearly fills the mature plastid. Material interpreted as a secretion appears at the surface of plastids, migrates, and accumulates along the cell surface adjoining the secretory cavity. Extrusion of the material into the secretory cavity occurs directly through the plasma membrane-cell wall barrier.     

Ultrastructural features of the salt gland of Tamarix aphylla L.

Summary The salt gland in Tamarix is a complex of eight cells composed of two inner, vacuolate, collecting cells and six outer, densely cytoplasmic, secretory cells. The secretory cells are completely enclosed by a cuticular layer except along part of the walls between the collecting cells and the inner secretory cell. This non-cuticularized wall region is termed the transfusion are (Ruhland, 1915) and numerous plasmodesmata connect the inner secretory cells with the collecting cells in this area. Plasmodesmata also connect the collecting cells with the adjacent mesophyll cells.There are numerous mitochondria in the secretory cells and in different glands they show wide variation in form. In some glands wall protuberances extend into the secretory cells forming a labyrinth-like structure; however, in other glands the protuberances are not extensively developed. Numerous small vacuoles are found in some glands and these generally are distributed around the periphery of the secretory cells in association with the wall protuberances. Further, an unusual structure or interfacial apparatus is located along the anticlinal walls of the inner secretory cells. The general structure of the gland including the cuticular encasement, connecting plasmodesmata, interfacial apparatus, and variations in mitochondria, vacuoles, and wall structures are discussed in relation to general glandular function.     

The terpene-producing glands of a Phasmid insect. Cell morphology and histochemistry

The defensive glands of Anisomorpha buprestoides produce the terpene toxicant anisomorphal. Each gland consists of a cuticular secretion reservoir surrounded by the secretory epithelium and the musculature which serves to compress the gland and expel the secretion. Two types of cells make up the secretory epithelium: a squamous layer next to the cuticular reservoir and a layer of larger secretory cells responsible for production of the toxicant. The microvilli-laden plasma membrane of each secretory cell is invaginated to form a central cavity. It appears that secretory products pass into the central cavity and then flow out to the gland reservoir via an efferent cuticular ductule contained within the squamous epithelial cell. Histochemical techniques demonstrate lipid reserves, carboxylic esterases, a variety of phosphatases, and an alcohol dehydrogenase, within the secretory cells. It is suggested that the lipid reserves are precursors of the terpenoid toxicant, that a mevalonic kinase has been histochemically demonstrated by the phosphatase test, and that an unusual alcohol dehydrogenase is active in the final steps of toxicant synthesis. The histochemical evidence is consistent with the hypothesis that anisomorphal is produced via the mevalonic acid pathway.     

Rosette glands in the gills of the grass shrimp,Palaemonetes pugio. I. Comparative morphology,cyclical activity,and innervation

Two types of exocrine rosette glands (called type A and type B), located in the gill axes of the grass shrimp Palaemonetes pugio, are described. The type A glands are embedded within the longitudinal median septum of the gill axes, whereas the type B glands typically project into the efferent hemolymph channels of the gill axes. Although both glands have certain common characteristics (i.e., a variable number of radially arranged secretory cells, a central intercalary cell, and a canal cell that forms the cuticular ductule leading to the branchial surface), they differ in the following respects. The type B gland is innervated, but the type A gland is not; axonal processes, containing both granular (ca. 900–1300 Å) and agranular (ca. 450–640 Å) vesicles, occur at a juncture between adjacent secretory cells and the central cell of the type B gland. The secretory cells of type A and type B glands differ in their synthetic potential and membrane specializations. These differences are more pronounced in well-developed, mature glands, most frequently encountered in larger (24–28 mm, total length) grass shrimp, than in the underdeveloped, immature glands that are most abundant in smaller (14–18 mm, total length) grass shrimp. Thus, in mature glands, the secretory cells of the type A rosette glands are characterized by extensive RER, abundant Golgi, and numerous secretory granules, whereas the secretory cells of the type B gland are characterized by extensively infolded and interdigitated basal plasmalemmas and by the presence of numerous mitochondria. In general, both types of glands exhibit increased secretory activity soon after ecdysis. The central and canal cells in both glands seem to have a role in the modification of the secreted materials. The possible functions assigned to the type A gland and the type B gland include phenol-oxidase secretion and osmoregulation, respectively.     

Ultrastructure of venom glands in the frog (Rana esculenta)

Electron microscopic study of skin venom glands in the frog, Rana esculenta, revealed the syncytial structure of the inner (secretory) wall which presents two distinct zones: a basal (juxtamuscular) one, which contains nuclei and major cytoplasmic organelles, and an apical one where large electron-dense granules form and accumulate. Granules are seen to arise inside clusters of tightly packed smooth endoplasmic reticulum (SER) elements, which suggests that the SER system is mainly involved in synthesis of this material. A high glutaraldehyde concentration (5%) also reveals a poorly defined material filling the intergranular cytoplasm. No apical limits to the syncytium could be traced, which suggests massive holocrine secretion. Nerves insinuate between the muscle cells and occur all along the internal face of the muscular layer, sometimes in close contact with the syncytium. The gland duct, the wall of which consists of epidermal cells, is blocked, in contact with the gland, by an epidermal bud linked externally to the muscle layer surrounding the gland. Thus, only strong muscle tension such as to expel all or part of the epidermal bud can trigger granule release. This phenomenon can be induced by the subcutaneous injection of epinephrine, but the high and distressing dose needed to provoke appreciable changes in venom glands renders unlikely any natural intense venom release triggered by epinephrine in the frog.     

Clasper gland morphology and development in Potamotrygon magdalenae (Elasmobranchii: Potamotrygonidae)

Clasper gland morphology and development in Potamotrygon magdalenae and its relation with the acquisition of reproductive maturity is described in males of different developmental stages (embryos, neonates, juveniles, and reproductively active and resting adults). The glands are subcutaneous masses in the proximal base of each clasper. They are partially bilobate organs with a ventral groove that bears a row of papillae. Glands tend to be asymmetric, the left gland has a larger size, a trend that has been observed in other organs of elasmobranchs. Glands are formed by radially organized tubular secretory units lined with a simple columnar epithelium with basal nuclei and granular eosinophilic cytoplasm; vascularized loose connective tissue surrounds the gland units. The gland is covered by two layers of striated muscle tissue in circular and longitudinal arrangement. The clasper glands begin to develop in neonates and their secretory activity begins in juveniles. The active secretion of the clasper gland is observed in mature males, it includes glycoproteins and sulfated mucopolysaccharides. The size of the glands has a positive and direct relationship with body size, measured as disc width. Significant differences in clasper gland size were found between mature (active and resting) and immature (neonates and juveniles) males, suggesting that the acquisition of the sexual maturity involves the increase in the size of the gland due to a highly augmented secretory activity. Therefore, clasper glands are clearly associated with the reproductive activity of males and their secretion should have an endocrine control as other sexual secondary organs. J. Morphol. 278:369–379, 2017. © 2017 Wiley Periodicals, Inc.     

Functional morphology of the mammiliform penial glands ofLittorina saxatilis (Gastropoda)

Summary The functional morphology of the mammiliform penial glands ofLittorina saxatilis has been investigated with both light and electron microscopy. These penial glands line the ventral edge of the penis and orient with the female mantle during copulation. Secretions are released from the penial glands to this interface where they probably function in adhesion. The penial gland secretions comprise heterogeneous granules as well as apocrine and mucous secretions. The heterogeneous granules are produced in separate multicellular glands arranged in a series of lobes that lie outside a thick smooth muscle layer enclosing the lumen. Each glandular lobe is surrounded by a thin layer of smooth muscle. Secretions are transported in individual cellular processes that pass through the thick smooth muscle layer and empty into the lumen. Surrounding the lumen is an epithelium containing apocrine secretory cells as well as occasional goblet-type, mucous cells. The combined action of the muscles forces secretions out of the lumen through the penial papilla, onto the external surface of the mammiliform penial gland. Longitudinal muscles extend into the penial papilla enabling its protrusion or retraction. Retraction of the penial papilla following secretion release is thought to create negative pressure beneath the penial gland producing suction adhesion. The visco-elastic properties of the penial gland secretion are qualitatively different from foot mucus and may represent specialization to an adhesive function.     

The structure of the salt gland of Aegiceras corniculatum

Summary The salt glands of Aegiceras corniculatum have been examined by light- and electron-microscope techniques. A gland consists of a large number of abutting secretory cells and a single, large basal cell. The secretory cells and basal cell are joined by well defined plasmodesmata. The glandular cuticle shows differences between the top and sides of the gland, which may indicate a variation in the nature or quality of wax deposited. These variations may be significant in the secretion process, in view of the lack of evidence for the presence of pores. In ultrastructure, the secretory cells are generally similar to others that have been described, though there is no evidence of any particular association of vacuoles within these cells.     

The anal glands of Rhapidostreptus virgator (Diplopoda: Spirostreptidae)

Summary In Rhapidostreptus virgator exocrine gland complexes are found in the anal valves of both sexes. Every gland complex consists of about 200 secretory units, each of which is comprised of four cells: two secretory cells, an intermediary cell, and a canal cell. The amount of secretion produced by these glands varies during the intermoult cycle: it is very small in freshly moulted individuals (postmoult phase), at a medial level during the following intermoult phase, and very large in the premoult phase. The secretion may be used to form the excrement clumps and above all to build the moulting chamber.     

Epidermal glands in Squamata: morphology and histochemistry of the pre-cloacal glands in Amphisbaena alba (Amphisbaenia)

Summary Pre-cloacal glands occur in some species of amphisbaenians. Although these glands are important in systematics, their biology and chemistry are little known. The pre-cloacal glands of Amphisbaena alba are of the holocrine type. They are made up of a glandular body and a duct. The glandular body is conical to elongate and is formed of clongatc lobules separated one from another by collagen septa. Each lobule is composed, at its periphery, of germinative cells, and within of polyhedral secretory cells, of different degrees of differentiation. The germinative cells, set on a basal lamina, are basophilic and their cytoplasm is fairly electron dense. The polyhedral cells display bulky cytoplasm, filled with spherical granules, wrapped in membranes and differing in their electron densities. Towards the lumen of the gland, these granules are increasingly eosinophilic and have an affinity for orange G. The secretion is discharged into the duct leading to the pore, which is situated in the central region of the scale. This secretion shows positive histochemical results for mucopolysaccharides and proteins. The similarity between the epidermal glands of lizards and those of A. alba raises the suggestion that the glands have equivalent functions, possibly in the course of intra- or interspecific communication.     

Morphological characterization of female accessory sex glands of Eupolybothrus fasciatus (Newport) (Chilopoda Lithobiomorpha)

The female reproductive system of Eupolybothrus fasciatus (Newport) (Chilopoda Lithobiomorpha) includes three types of well-developed accessory glands, viz. large glands, small glands, and the periatrial gland. External morphology and the ultrastructural organization of these glands have been investigated by light and electron microscopy. The small and large glands are paired and have coiled ducts that open, respectively, into and externally to the genital atrium. By contrast, the periatrial gland is unpaired and is located on the ventral wall of the atrium into which it opens via several small canals. Ultrastructural features show that all three glands consist of two different types of cells: secretory cells and ductule cells. The secretary cells contain prominent secretory granules and are similar to a class of insect epidermal gland cells (class 3) organized as acini surrounding an extracellular lumen into which microvilli project. The granules, which have different morphological features in each gland, could be responsible for important differential functions such as producing a sexual attractant, providing a coating material that protects eggs laid on the ground, and contributing to a fluid that digests spermatophores. © 1996 Wiley-Liss, Inc.     

Peculiar salivary glands in a silk‐producing mite Bakericheyla chanayi (Cheyletidae)

This is the first ultrastructural investigation of salivary glands in the family Cheyletidae. In both sexes of Bakericheyla chanayi, paired acinous salivary glands and tubular coxal glands were shown to be united into the common podocephalic system. The secretory portion of the salivary gland includes medial and lateral lobes composed of the five and two cells, respectively, with clearly distinct ultrastructure. The cytoplasm of the cells is occupied by the secretory granules containing fine fibrous material. The fine structure of both cell types suggest a proteinaceous nature of their secretions. A single central process extending from the apical face of each secretory cell passes through the common acinar cavity to enter the conducting duct. A pair of intercalary cells at the base of the conducting duct links it with the secretory portion of the gland. Extending towards the acinar cavity, protrusions of intercalary cells alternate the apical regions of the secretory cells and form with them highly‐specialized contacts characterized by the apical network of microtubules and microfilaments. Two possible ways of secretion are suggested: 1) exocytosis into the acinar cavity and 2) direct passage via the central processes. The detection of axon profiles in the gland body suggests a neural control for the glandular cell function. In tritonymphs, neither secretion nor large lateral lobe cells were observed up to the pharate stage when the lateral lobe undergoes rapid differentiation. The arrangement of the acinous gland is compared to that of other arthropods. Its composition appears to be close to the class three of insect glands. The involvement of the lateral lobe cells in silk production is discussed. J. Morphol. 276:772–786, 2015. © 2015 Wiley Periodicals, Inc.     

CUTICLE DEVELOPMENT ON GLANDULAR TRICHOMES OF CANNABIS SATIVA (CANNABACEAE)

The dermal sheath of glandular trichomes of Cannabis sativa L., consisting of cuticle and a subcuticular wall, was examined by transmission electron microscopy. Cuticle thickened selectively on the outer wall of disc cells of each trichome prior to formation of the secretory cavity, whereas thickening was less evident on the dermal cells of the bract. Membraned secretory vesicles that differ in size and appearance in the secretory cavity were the source of precursors for synthesis of cuticle. Vesicle contents, released following the degradation of the vesicle membrane upon contact with the subcuticular wall, contributed to both structured and amorphous phases of cuticle development. The structured phase was represented by deposition and thickening of cuticle at the subcuticular wall-cuticle interface to form a thickened cuticle. In the amorphous phase precursors permeated the cuticle in a liquid state, as shown by fusion of cuticles and wax layers between contiguous glands, and may have contributed to growth in surface area of the expanding sheath. Disc cells are interpreted to control growth of secretory cavity by secretion of membraned vesicles into the cavity. The thickened cuticle, which increased eightfold in thickness during enlargement of the gland, provided structural strength for the extensive surface area of the dermal sheath. The gland of Cannabis in which vesicle contents contribute to the growth in thickness and surface area of the cuticle of the sheath is interpreted to represent a phylogenetically derived state as contrasted to secretory glands possessing only cuticle and lacking a complement of secretory vesicles.