Ultrastructure of the anterior alimentary tract of a monogenean, Diclidophora merlangi

The anterior alimentary tract of Diclidophora merlangi is composed of a complex series of morphologically distinct epithelia interconnected by septate desmosomes and penetrated by the openings of numerous unicellular glands. The mouth and buccal cavity are lined by an infolding of modified body tegument, distinguished by uniciliate sense receptors, buccal gland openings, and in the buccal region by a dense, spiny appearance. The prepharynx is covered by an irregularly folded epithelium and, for part of its length, by the luminal cytoplasm of the prepharyngeal gland cells. The epithelium is syncytial and pleiomorphic, and regional variation in structure is common. A separate epithelium invests the lips of the pharynx and its free surface is greatly amplified by numerous, dense lamellae of varying dimensions. The lip epithelium is continuous with cytoplasmic processes of cells located external to the pharynx. A further, distinct epithelium borders the pharynx lumen and is composed of discrete cytoplasmic units connected by short septate desmosomes. The oesophagus is lined by a modified caecal epithelium, lacking haematin cells, and, in places, is perforated by the openings of oesophageal gland cells; it is continuous with the syncytial connecting tissue of the gut caeca.     

An ultrastructural study of the cercarial excretory system in Bucephaloides gracilescens and Prosorhynchus squamatus

The ultrastructure of the flame cells, capillaries, collecting tubes, excretory bladder, excretory atrium, caudal vesicle, lateral caudal ducts and excretory pores of cercariae of Bucephaloides gracilescens (Rudolphi, 1819) Hopkins, 1954 and Prosorhynchus squamatus Odhner, 1905 (Digenea: Bucephalidae) is described. Both species are essentially similar except for some details. The terminal parts of the protonephridia have all the structural features that are typical of trematodes. The collecting tubes in the cercarial body are composed of cells that are wrapped around the lumen. The main collecting tubes are joined to the excretory bladder syncytium by septate junctions. Features of P. squamatus excretory bladder epithelium indicate that it is involved in secretory activity, but this is not the case in B. gracilescens. In both species the luminal surface of the excretory bladder epithelium is increased by lamellae, and the basal plasma membrane forms invaginations. In the bladder syncytium of P. squamatus both apical lamellae and basal invaginations are more developed and mitochondria are also more numerous. The excretory atrium is lined by a syncytium with nucleated cytons located in the surrounding parenchyma. The atrium lining is not continuous with the body tegument and possesses specific secretory inclusions and a thick glycocalyx. Septate junctions connect the atrium syncytium to the excretory bladder epithelium at its anterior end and to the syncytial excretory epithelium lining the caudal vesicle and the lateral caudal ducts at its posterior. In the excretory pores the caudal duct syncytium is joined to the tegument by septate desmosomes.     

日本沼虾生精细胞与支持细胞之间的连接关系

用透射电镜技术研究了日本沼虾精子发生过程中不同细胞之间的连接关系。结果表明,从精原细胞期到次级精母细胞期,在生精细胞之间存在间隙连接与分隔连接与分隔连接,并且两种连接相互邻接,桥粒仅在精原细胞之间发现;从精原细胞期到精细胞期,在生精细胞与支持细胞之间也存在相互邻接的间隙连接与分隔连接,两类细胞之间有大量桥粒,形成血淋巴－精巢屏障,这种屏障可保持生精细管内环境的稳定性;精子发生的不同时期,支持细胞之     

Fine structure of the rectal pads in the desert locust Schistocerca gregaria with reference to the mechanism of water uptake

The rectal pads of Schistocerca gregaria are composed of three different cell types: epithelial, secondary and junctional cells. The rectal pads are interconnected by simple rectal cells and both are lined internally by a articular intima. The epithelial cells exhibit extensive infoldings of the apical plasma membranes that are closely associated with mitochondria. Their lateral plasma membranes are highly folded around large mitochondria and enclose intercellular channels and spaces. They are united by belt and spot desmosomes, septate junctions, gap junctions and scalariform junctions, but terminate in a basal syncytium without contacting the basal plasma membranes. The apical and basal cytoplasm contain coated vesicles, dense tubular elements, multivesicular bodies and lysosomes, suggesting receptor-mediated endocytosis of small peptide molecules into the epithelial cells. The apical membrane infoldings of the secondary cells are also associated with large mitochondria. Their basal plasma membranes are covered by connective cell processes and connected with them by spot desmosomes which may be involved in solute recycling. The presence of neurosecretory-like axons near the secondary cells suggests that they exert local control on the function of these cells. The ultrastructural details are examined in relation to their role in solute and water transport.     

Ultrastructure of the foregut and associated glands of Calicotyle kröyeri (Monogenea: Monopisthocotylea)

The mouth, pharynx and oesophagus of Calicotyle are lined by syncytial epithelia, and there are numerous unicellular glands associated with the oesophagus. An infolding of unmodified external tegument lines the mouth cavity and is connected by discrete cytoplasmic processes to subjacent perikarya. It contains two types of secretory body and its luminal surface is invested with a finely filamentous coating. The pharynx and oesophagus are lined by irregularly-folded epithelia that are interconnected by a septate desmosome. Membranous inclusions distinguish the pharynx epithelium and there is a well developed basal lamina for insertion of the pharyngeal muscles. The oesophagus epithelium is perforated by the openings of the oesophageal glands. These lie in the surrounding parenchyma and produce a dense, membrane-bound secretion which is conveyed by duct-like extensions of the glands to the oesophagus lumen. The ducts are supported in places by microtubules and are anchored to the oesophageal epithelium by septate desmosomes. A septate desmosome also marks the junction between the epithelium and the gut caeca.     

Ultrastructure of the tegument of the metacercaria of Timoniella imbutiforme

The spinous body tegument of the metacercaria of Timoniella imbutiforme (Molin, 1859) is described in detail and found to comprise an outer tegumental syncytium connected to subjacently situated subtegumentary 'cells'. There are four types of secretory bodies in the outer syncytial layer as well as serrated overlapping spines and mitochondria. The subtegumentary 'cells' are characterized by the presence of four secretory body types as well as giant bodies which may be involved in the elaboration of the secretory bodies or spine material. The normal configuration of the somatic muscles of T. imbutiforme show that the muscular machinery necessary for activity once the larval stage becomes excysted is already in place. The sensory endings are found to be of the uniciliate type occurring in groups of up to eight in raised domes distributed over the body. Secretory gland cells are numerous and possess long ducts connected to the basal lamina of the outer syncytial layer via septate desmosomes.     

Ultrastructure of the protonephridia of Seison annulatus (Rotifera)

Summary Each of the two protonephridial systems of Seison annulatus consists of three sections which are separated by cell borders with septate junctions: (a) a terminal syncytium with eight terminal organs and a capillary canal, (b) a canal syncytium which is divided into a multiciliary canal region and a main canal region, and (c) a nephroporus cell. The terminal syncytium is branched and linked twice to the canal syncytium. The supporting structure of each filtration barrier is a hollow cylinder which is perforated by pores and lacks microvilli (pillars). A protonephridial spine is situated in the multiciliary canal region and stabilizes the neck region. The ored, hollow cylinder and the protonephridial spine are new characteristics for the Rotifera.     

Intercellular junctions in the hypodermis,salivary gland and gené's organ of the cattle tick,Boophilus microplus

Summary The intercellular junctions that occur in the hypodermis, Gené's organ, and the salivary glands of the tick, B. microplus, are described. The epithelial cells of the hypodermis are connected by spot desmosomes and septate junctions and the secretory cells of Gené's organ by septate and gap junctions. The cap cells in the alveoli of the salivary gland connect to adjacent cells by gap junctions, hemidesmosomes and septate junctions into which microtubules are inserted.The authors would like to thank Mr. R. Lamb for preparing the plates. M.W.J. Megaw was supported by an S.R.C. Studentship     

Fine structure and function of the digestive tract of Cyathura carinata (Krøyer) (Crustacea,Isopoda)

Summary The entire gut of Cyathura carinata is lined by a cuticle indicating its completely ectodermal origin. By flattening of the epithelial folds and possibly also of reserve-folds of the plasma membrane the intestine is highly dilatable, an adaptation towards a rapid uptake of the food which is sucked in by means of specialized mouthparts, which pierce the body wall of its main prey, the polychaete Nereis diversicolor. Bundles of microtubules within the intestinal cells presumably represent cytoskeletal structures providing protection against mechanical stress. Spirally arranged muscle fibres, which form peculiar contact areas with the gut, can easily follow any dilatation. A few indications of the metabolic functions of the anterior gut epithelium have been found: Basally and apically located labyrinthine structures of the plasma membrane, apically located clear vesicles, positive reactions for lysosomal, mitochondrial and membraneous enzymes, a strikingly thin and loosely arranged cuticle through which food substances of low molecular weight may diffuse. The cells of the gut and also of the digestive caeca are interconnected by desmosomes, extensive pleated septate junctions, and gap junctions. In the pleon the gut is less dilatable and devoid of plasma membrane specializations. In this area tendon cells, particularly rich in microtubules, serve as attachment sites for the dilating muscles of the rectum. The digestive caeca synthetize and secrete digestive enzymes, mix food and enzymes in their lumen, resorb food molecules, store lipids and glycogen. In the glandular epithelium small cells, rich in rough ER, and a majority of large cells, rich in lipid droplets, occur which, however, are interconnected by a series of morphologically intermediate cells. All cells bear an apical brush border, form a basal labyrinth and contain high to medium activities of acid phosphatase, nonspecific esterases, ATPase, and succinic dehydrogenase. The ER-rich cells are far less frequent than in the omnivorous or herbivorous isopods (Sphaeroma, Idothea, Asellidae, Oniscoidea).     

Freeze-fracture,ultrastructural and autoradiographic analysis of the ventral prostate glands in castrated mice

Summary Ultrastructure of the ventral prostate glands was studied in mice castrated for 1 through 60 days and for 11 and 17 months and in age-matched normals. We have described freeze-fracture and ultrastructural characteristics of acinar epithelial cells in addition to the patterns of thymidine incorporation in the cells of castrates and normal animals. Our study has shown a biphasic pattern of prostatic involution in the long-term castrated mice. In castrates the initial atrophy of prostate glands occurred by sloughing of the apical portions of columnar cells, autophagia of the cytoplasmic organelles as well as by occasional sloughing of the individual cells into the acinar lumen. Concurrent with the initial atrophy, the glands and stroma were infiltrated by neutrophils and lymphocytes. The cell loss by sloughing and leucocyte infiltration of glands became infrequent in 7- to 21-day castrates. However, the cell loss by sloughing increased secondarily in mice castrated for 21 to 37 days along with the increased leucocyte infiltration of the glands. The cell loss became minimal in castrates of 60 days and beyond. Our evidence suggests that the cell loss by sloughing was an active process in the involution of prostate glands which also showed differential sensitivity to castration stimuli in mice.This research was supported by Medical Research Service of Veterans Administration     

Intercellular Attachment in the Epithelium of Hydra As Revealed by Electron Microscopy

In Hydra adjacent epithelial cells are bound firmly to each other by desmosomes of a type not described in detail hitherto. The most prominent feature of these desmosomes is the presence of a series of parallel lamellae which bridge the intercellular space and connect the two apposed cell surfaces directly. These structures, here termed intercellular attachment lamellae, display two peaks of density about 50 A apart. These dense lines appear in some instances to be continuous with the outer dense components of the plasma unit membranes of the attached cells. The presence of prominent lamellae in intercellular attachments is sufficiently distinctive to deserve special terminology; accordingly, the term septate desmosome is proposed. It is noted that septate desmosomes may have been seen in other animals in instances where published electron micrographs show cross-striations or prominent connections in regions of intercellular attachment. It is suggested that septate desmosomes in Hydra, in addition to binding cells firmly to each other, form barriers to the movement of water into intercellular spaces and thus help to protect the organism's internal environment. Observations on the use of phosphotungstic acid for improving contrast in materials embedded in epoxy resins are also recorded.     

Fasciola hepatica: Migration of newly excysted juveniles in resistant rats

Using transmission and scanning electron microscopy, the early migration of juvenile Fasciola hepatica was examined in naive and resistant rats. In naive rats, the migration of flukes to the peritoneal cavity was uneventful. In resistant rats, flukes were rapidly coated with antibody whilst still in the gut lumen and a proportion of the flukes were unable to penetrate the intestinal wall. Those that did penetrate were unharmed as they crossed the gut wall, but on entering the peritoneal cavity they were coated with antibody and host cells including eosinophils, neutrophils, macrophages, and mast cells. Eosinophils were seen degranulating onto the fluke surface, and this appeared to result in the erosion of the tegumental syncytium.     

Ultrastructural observations on mehlis' gland in the monogeneans, Diplozoon paradoxum and Calicotyle kröyeri

Mehlis' gland of both Diplozoon paradoxum and Calicotyle kröyeri is composed of two cell types that taper to form ducts opening into the lumen of the ootype. The cells are invested with fibrous interstitial material and form a close structural relationship with surrounding parenchyma. The most prevalent cell type, the S₁ cell, is characterized by an extensive GER with narrow cisternae containing a finely granular material, and numerous Golgi stacks involved in the formation of multi-vesicular secretory bodies. In the S₂ cells the GER cisternae are greatly distended with a finely filamentous material and the Golgi give rise to dense secretory bodies with a packed fibrous appearance. There are species differences in the fine structure of the secretory bodies and these may reflect differences in the chemical composition of the glands. The ducts of the glands are lined with microtubules and are anchored to the ootype epithelium by septate desmosomes. They convey the secretory products to the ootype where they are released, apparently by exocytosis involving membrane fusion, into the lumen. The ootype is lined by a highly folded cellular epithelium which in D. paradoxum is ciliated. The cells contain profiles of GER and Golgi complexes and produce a third type of secretion which is also discharged into the ootype lumen.     

Tissue healing and septate desmosome formation in hydra

Tissue healing was studied in hydra tissue grafts by means of light and electron microscopy. Healing is begun by the gastrodermis: subsequently the epidermis fuses and the mesoglea is repaired. Epidermis fusion is first brought about by long processes from the basal portions of the epithelial cells bridging the wound gap and adhering to opposing cells. Irregular septate desmosomes form early in this process and continuously become more neatly organized. Concommitant with the healing process at the graft site, neighboring cells are also rearranging, their septate desmosomes undergoing transient disorganizations. We conclude that the organization of septate junctions is dynamic, and may be undergoing a balanced but continuous, steady state turnover. During the healing process the forces acting on the desmosomes, and other aspects of the cells' architecture, are not balanced, and the junctions grow and become more highly organized.     

The ultrastructure of the statocysts in the pediveliger larvae of Pecten maximus (L.) (Bivalvia)

The pediveliger of Pecten maximus (L.) has a pair of statocysts situated at the base of the foot on either side of a bilobed pedal ganglion. The statocysts consist of a spherical sac connected to the mantle cavity by a cylindrical ciliated canal. Within the sac there are statoconia which are variable both in shape and structure. The cells of the sac are joined by septate desmosomes. There is a non-ciliated cell in each sac containing a variety of granules some of which resemble certain of the statoconia. The remainder of the sac is composed of hair cells, which bear a circular array of radiating cilia. The basal bodies and horizontal striated roots of these cilia are directed radially. The hair cells give rise to thin processes which probably join together to form the static nerve. This nerve runs from the static canal to the pleural ganglion.     

Studies on perineural junctional complexes and the sites of uptake of microperoxidase and lanthanum in the cockroach central nervous system

The perineurial junctional complexes in the nerve cord of Periplaneta americana have been shown to consist of septate desmosomes, extensive gap junctions and relatively limited regions of tight junctions. Microperoxidase (M.W. 1,900) undergoes limited intercellular penetration into the septate desmosomes. Lanthanum penetrates both the septate desmosomes and gap junctions. It is concluded that the restricted access of these substances to the underlying extracellular spaces results from the presence of the perineurial tight junctions. These results contrast with those for small peripheral nerves, which lack equivalent junctional complexes, and in which the extracellular spaces are found to be accessible to externally applied lanthanum. The results are discussed in relation to current concepts of the insect blood-brain barrier.     

Ultrastructure of the Male Accessory Glands and Sperm Ducts of Cylindrotaenia hickmani(Cestoda,Cyclophyllidea)

Abstract The ultrastructure of unicellular accessory glands (= prostate glands) and external male ducts of the cestode Cylindrotaenia hickmaniare described. Accessory glands open into the lumen of the external common sperm duct (= external vas deferens). The gland cells contain abundant endoplasmic reticulum, Golgi bodies and secretory bodies, and have elongate necks that pierce the apical cytoplasm of the duct. Cell contact with the apical cytoplasm of the sperm duct is mediated by septate desmosomes. Accessory glands secrete spherical particles, with a diameter of approximately 70 nm, that adhere to spermatozoa. The roles of these accessory glands may relate to activity of the sperm or development of the female system after insemination. Paired sperm ducts arise from testes, and unite to form a common sperm duct. Each duct consists of a tubular anucleate cytoplasmic region which is supported by nucleated cytons that lie sunken in the parenchyma. The apical cytoplasm of the paired sperm ducts (= vasa efferentia) possesses apical microvilli and abundant mitochondria, but few other cytoplasmic features. The apical cytoplasm of the common sperm duct possesses sparse apical microvilli and numerous electronlucent vesicles. The male gonoducts form an elongate syncytium which is markedly polarized along the length of the ducts. The ducts also display apical–basal polarity in that sunken nucleated cytons support the apical cytoplasm which in turn has distinct basal and apical domains.     

An ultrastructural study of the prostate gland of megascolicid earthworm Lampito mauritii (Kinberg)

The ultrastructure of prostate gland of Lampito mauritii revealed two types of secretory cells. Type 1 cells with a broad basal region and a long apical region contain electron dense oval secretory granules with an increased density at the core region. Numerous electron lucent granules with fine filamentous and electron dense amorphous materials also occur at the basal region of these cells. Type 2 cells contain electron lucent mucous-like secretory granules. This cell type contains exceptionally large Golgi complexes having 20-23 stacked cisternae. Both cell types open into a common lumen and numerous microtubules are visible at the apical end. Junctional complexes, such as desmosomes and septate junctions, are observed in this glandular tissue.     

Scanning electron microscopy of the spermatheca in Sitophilus granarius (L.)

With scanning electron microscopy the spermathecal organ of Sitophilus granarius (L.) has been examined. The only morphological attachment between this organ and other tissues is to the bursa copulatrix by the sperm duct and to the central nervous system by two nerve fibers. The nerves innervate the muscles connecting the two arms of the U-shaped spermatheca. Glandular cells are grouped together and are connected to the spermathecal lumen by a short collecting duct. Vascular sinuses opening from the body cavity into the body of the gland are observed as pores on the surface of the gland.     

Role of pleated septate junctions in the epithelium of miracidia of Schistosoma mansoni during transformation to sporocysts in vitro

The surfaces of miracidia of Schistosoma mansoni were examined ultrastructurally during in vitro transformation to sporocysts. Before transformation, the surface was composed of ciliated epithelial plates (EP) that were set into a reticulum of narrow syncytial ridges (SR). The EP were attached to SR by extensive pleated septate junctions that had 18-24 strands of intramembrane particles (IMP) on the protoplasmic faces and complementary pits on the ectoplasmic faces. These junctions also appeared to separate the EP plasma membrane into apical and basolateral domains with a larger number of IMPs on the latter. Transformation was induced by placing the miracidia in salt containing medium which also halted ciliary beating. In 2-5 hr, the SR expanded until they formed a syncytium covering the parasite surface, while the EP retracted and rounded up. During this time, the EP and SR were held in contact with one another by the septate junctions which became progressively convoluted. Subsequently, the EP detached from the parasite. When transforming miracidia were returned to fresh water, the cilia resumed beating and the EP detached from the parasite surface and exposed the underlying basement membrane. Those EP that remained attached were connected only by septate junctions to the expanded SR. These studies demonstrate that the formation of the syncytium occurs gradually with contact maintained between EP and SR via the septate junctions. Further, the septate junctions are similar to occluding junctions in mammalian epithelia since they segregate the plasma membrane of the EP and they have an adhesive function.