Ultrastructural Aspects of Spicule Formation in the Solitary Ascidian Herdmania momus (Urochordata,Ascidiacea)

The solitary stolidobranch ascidian Herdmania momus contains numerous calcium carbonate spicules in its tunic and body tissues. The slender body spicules form inside complex sheaths in the body wall and branchial basket, where they remain for the life of the animal. The much smaller tunic spicules form inside the tunic blood vessels and then migrate to the tunic surface, where they become anchored by their spiny base. This paper is an ultrastructural investigation of the formation of the body spicules; the tunic spicules, which apparently form quite differently, will be the focus of a future study. The body spicules are composed of rows of closely packed acicular spines which form completely extracellularly. The spine tips are covered by flattened, highly pseudopodial sclerocytes bound together by tightly interdigitating cell processes. The basal regions of contiguous spines are covered by very thin sclerocyte cell processes. An organic matrix is present within the spines; its exact nature is not clear. A very dense extracellular inter-spine matrix is located between the spine tips and the contiguous basal regions. Presclerocytes within the sheaths between the spicules are probably responsible for formation of the extracellular structures of the sheaths. The presclerocytes appear to aggregate and transform into sclerocytes at the apical end of the spicule. New spines are added at the apical end of the spicule as well as between larger spines. Comparisons are made between body spicule formation in H. momus and skeletogenesis in echinoids.     

ELECTRON MICROSCOPY OF THE HUMAN SYNOVIAL MEMBRANE

The structure of the lining cells at the surface of the synovial membrane facing the joint cavity has been studied by electron microscopy. The long cytoplasmic processes of these cells appear to be oriented toward the surface of the membrane, where they overlap and intertwine. The matrix of the lining cells contains dense material but no fibers with the periodicity of collagen. The lining cells are divided into two cell types or states of activity on the basis of their cytoplasmic contents. Type A is more numerous and contains a prominent Golgi apparatus, numerous vacuoles (0.4 to 1.5 microns in diameter) containing varying amounts of a dense granular material, many filopodia, mitochondria, intracellular fibrils, and micropinocytotic-like vesicles. Type B contains large amounts of ergastoplasm with fewer large vacuoles, micropinocytotic-like vesicles, and mitochondria. The probable functions of these cells are discussed in the light of current knowledge of the metabolism and function of the synovial membrane.     

Ultrastructure of the excretory tubes of the mite Macrocheles muscaedomesticae (Mesostigmata,Macrochelidae) with notes on altered mitochondria

The fine structure of the excretory tubes of the mesostigmatid mite Macrocheles muscaedomesticae were investigated. These paired tubes are partially ensheathed by fat body and invested throughout by a branching system of visceral muscles. The fine structure of the cells of the excretory tube is in general similar with only minor differences found throughout its length. The basal region of each epithelial cell of the excretory tube borders the hemocoel and is divided into many compartments by the extensive infolding of the plasma membrane. Mitochondria and vacuolar inclusions are often closely associated with these compartments. More than one morphological type of mitochondria was found distributed throughout the cells of the excretory tubes. The most commonly encountered type had well developed cristae and an electron dense matrix. Less commonly, mitochondria with somewhat poorly developed cristae and a translucent matrix often containing myelin-like figures of varying complexity were observed. It is suggested that they represent part of a normal process of mitochondrial degeneration. The apical region of the cell has a border composed of plate-like folds of the plasma membrane termed microlamellae. The lumen contains abundant granules of the excretory product.     

THE BASE OF THE PROXIMAL CONVOLUTED TUBULE CELLS OF RAT KIDNEY

The three dimensional arrangement of the compartments on the base of proximal convoluted tubule cells of rat kidney is described. An extracellular basal labyrinth is found to be enclosed by these compartments. The compartments with their mitochondria and the basal labyrinth are regarded as forming a functional unit. It is supposed that this basal unit serves for excretion of reabsorbed fluid from the cell into the labyrinth and for the development of hydrostatic pressure in the labyrinth to overcome the capillary pressure and to pass the reabsorbed fluid into the blood stream.     

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.     

锯缘青蟹精子发生的超微结构

采用透射电镜观察锯缘青蟹精子发生过程中超微结构的变化,结果表明：精原细胞椭圆形,染色质分布于核膜周围,胞质中具嵴少的线粒体,内质网小泡等。初级精母细胞染色质呈非浓缩状,胞质中具众 内质网小泡,特殊的膜系及晶格状结构。次级精母细胞核质间出现由内质小泡聚集成的腔。     

THE FINE STRUCTURE OF EPENDYMA IN THE BRAIN OF THE RAT

The ciliated ependyma of the rat brain consists of a sheet of epithelial cells, the luminal surface of which is reflected over ciliary shafts and numerous evaginations of irregular dimensions. The relatively straight lateral portions of the plasmalemma of contiguous cells are fused at discrete sites to form five-layered junctions or zonulae occludentes which obliterate the intercellular space. These fusions occur usually at some distance below the free surface either independently or in continuity with a second intercellular junction, the zonula adhaerens. The luminal junction is usually formed by a zonula adhaerens or, occasionally, by a zonula occludens. The finely granular and filamentous cytoplasm contains supranuclear dense bodies, some of which are probably lysosomes and dense whorls of perinuclear filaments which send fascicles toward the lateral plasmalemma. The apical regions of the cytoplasm contain the basal body complexes of neighboring cilia. These complexes include a striated basal foot and short, non-striated rootlets emanating from the wall of each basal body. The rootlets end in a zone of granules about the proximal region of the basal body, adjacent to which may lie a striated mass of variable shape. All components of the basal body complex of adjacent cilia are independent of each other.     

THE FINE STRUCTURE OF VON EBNER''S GLAND OF THE RAT

The fine structure of von Ebner's gland was studied in untreated rats and rats stimulated to secrete by fasting-refeeding or injection of pilocarpine. Cytological features were similar to those reported for pancreas and parotid gland. Abundant granular endoplasmic reticulum filled the basal portion of the cell, a well-developed Golgi complex was located in the vicinity of the nucleus, and the apical portion of the cell was filled with dense secretory granules. Dense heterogeneous bodies resembling lysosomes were closely associated with the Golgi complex. Coated vesicles were seen in the Golgi region and also in continuity with the cell membrane. Granule discharge occurred by fusion of the granule membrane with the cell membrane at the secretory surface. Successive fusion of adjacent granules to the previously fused granule formed a connected string of granules in the apical cytoplasm. Myoepithelial cells were present within the basement membrane, and nerve processes were seen adjacent to acinar and myoepithelial cells. Duct cells resembled the intercalated duct cells of the major salivary glands.     

FINE STRUCTURE OF THE MYOEPITHELIUM OF THE ECCRINE SWEAT GLANDS OF MAN

The secretory coils of glutaraldehyde-osmium tetroxide-fixed and Epon-Araldite-embedded eccrine sweat glands from the palms of young men were studied with the electron microscope. The myoepithelial cells lie on the epithelial side of the basement membrane and abut other epithelial elements directly. The irregularly serrated base of the cell has dense thickenings along the plasma membrane which alternate with zones bearing pits; the smooth apical surface lacks dense thickenings, is studded with pits, and conjoined to secretory cells by occasional desmosomes. Masses of myofilaments, 50 A in diameter, fill most of the cell and are associated with irregular dense zones. In cross-section the arrangement of the myofilaments seems identical with that of the I band of striated muscle, and the dense zone has typical Z band structure. A few microtubules and cytoplasmic cores bearing profiles of the endoplasmic reticulum, filamentous mitochondria, and glycogen granules penetrate the fibrillar masses and run parallel to the oriented myofilaments. In the perinuclear zone, Golgi membranes, rough- and smooth-surfaced elements of the endoplasmic reticulum, mitochondria, glycogen, microtubules, lipid, pigment, and dense granules are variable components in the cytoplasm. The interrelationships of the myoepithelial cells with the secretory cells suggest that the former may act as regulators, controlling the flow of metabolites to the secretory epithelium.     

Comparative scanning and transmission electron microscopy studies of the ependyma of the central canal in the spinal cord of primates. I. Electron optical image of the ependyma in the central canal of the spinal cord of the callithrix monkey (Callithrix jacchus, Linné 1758)

The ependyma lining the central canal of the spinal cord of adult males and females monkey, Callithrix jacchus, was examined by scanning and transmission electron microscopy. The cross section of the lumen of the central canal are round, oval, or triangular. Light and dark ependymal cells, depending on the density of the cytoplasm, were found. The light ependymal cells are fewer than the dark cells. The ependyma cytoplasm contained numerous mitochondria, filamentous structures, one or more well-developed Golgi-complexes, vesicles of the smooth endoplasmic reticulum, ribosomes, lysosomes, multivesicular bodies, profiles of the rough endoplasmic reticulum, large osmophilic bodies, and microtubules. The nuclei of the ependyma cells usually have a simple, regular round or oval shape. They occupy a relatively large portion of the cell volume and lie in the central or mediobasal position. Some of the nuclei show deep invaginations into the karyoplasm. Most of the mitochondria occupy mainly the supranuclear portion of the apical cytoplasm. There are of the crista-typ. Ribosomes occur free in the cytoplasm, but some attached to the profiles of the rough endoplasmic reticulum or being arranged as polysomes. The filamentous structures are generally prominent cytoplasmic components and are distributed at the apical, lateral, or basal region of the ependymocytes. They are grouped into bundles and arranged in parallel arrays. Some of these bundles reach the plasmamembrane at the free lumina of the central canal, others take contact to the filamentous structures of the zonulae adherentes of the junctional complex below the free surface. The granular endoplasmic reticulum shows specializations. There profiles surrounding granular substances and widely distributed granulations in connection with the nuclear envelope. The functional significance of the deposition of these granulations is still unknown. The luminal surface of the ependymocytes bears many microvilli and cilia. The cilia are regularly arranged in cranio-caudal direction. Each cilium has the typical (9 + 2)-subfibres. The intercellular space at the surface of the ependymal layer shows a single zonula adherens or zonulae adherentes in the row. Tight junctions and gap junctions were not found in the material examined. Cell processes of liquor contacting neurons between adjacent ependyma cells, protruding into the lumen of the central canal, could be observed. The termination of these neurons contains accumulations of mitochondria in the central part, large amounts of vesicles, and small dense bodies. They have short microvilli and some stereocilia at the free surface.(ABSTRACT TRUNCATED AT 400 WORDS)     

Isoparorchis hypselobagri: ultrastructure of the tegument and associated tissues in a digenean inhabiting a gaseous aerobic environment

Adult I. hypselobagri live in the swim bladder of the Indian catfish Wallago attu, a gaseous environment with a relatively high oxygen content. The ventral tegument, which in life is applied close to the swim bladder wall, is relatively unspecialized, showing typical ultrastructural features of the digenean surface. The dorsal tegument, which is exposed to the oxygen-rich surroundings, has numerous pyriform extensions of superficial parenchymal cells closely applied to the base of the surface syncytium. These extensions bear numerous mitochondria and send finger-like processes deep into the basal cytoplasm of the syncytium where they interdigitate with corresponding infolds of the basal tegument membrane. The pyriform parenchymal extensions are connected with underlying nucleated cell bodies via irregular glycogen-filled tubular processes, many of which end blindly in the interstitial tissue or expand into glycogen-filled bulbs beneath the cell bodies. These superficial parenchymal processes associate at gap junctions with ramifications of a distinct deeper parenchymal tissue which contains lipid, residual bodies and glycogen. The dorsal tegument and associated structures may constitute a respiratory organ, taking advantage of molecular oxygen diffusing across the surface syncytium to carry out aerobic energy transduction in the superficial parenchymal extensions. ATP so generated may diffuse inwards for distribution throughout the body in the deep parenchymal tissue. The extensive network of ramifying cytoplasmic tubules is supported by a fibrous matrix of interstitial tissue.     

The fine structure of the follicular cells in growing and atretic ovarian follicles of the domestic goose

Summary The structure of follicular layer of growing and atretic follicles in the ovary of the domestic goose, was studied by electron microscopy. In small follicles, the wall is lined with a narrow layer of tightly packed small, cuboidal cells separated from the thecal tissue by the basal lamina. During growth, they transform into tall, columnar cells arranged in a single row. The cells display several peculiar ultrastructural features. First, annulate lamellae are commonly observed. Second, cytoplasmic dense-cored granules accumulate in close association with fenestrated cisternae and networks of tubuli derived from the RER. They consist of spheres and strands of amorphous substance of unknown origin. Third, the cells contain many transosomes, a unique organelle of the avian follicle cell consisting of a dense plaque associated with ribosome-like particles. The mature forms of transosomes are located at the tips of lateral and apical cell projections, while bodies thought to be their precursors, are found in the apical cytoplasm. In follicles larger than 8 mm in diameter, most of the transosomes and their precursors have disappeared. Follicular atresia occurs in all of the size-classes of follicles investigated. A loss of transosomes (in follicles up to 8 mm in diameter) and an accumulation of lipid droplets are the first atretic events detectable by electron microscopy. Morphologic features, including deep nuclear indentations, accumulation of lipid droplets frequently encireled by membrane whorls, dilation and disintegration of RER cisterns, swelling of mitochondria and accumulation of dense irregular masses of unknown origin in the cytoplasm, are taken as evidence for advanced degradation. We conclude that necrosis is the dominant type of cell death of the follicular cells during atresia. However, a small fraction of cells, characterized by dark condensed cytoplasm, seems to die by apoptosis.     

THE FINE STRUCTURE OF THE AXON AND GROWTH CONE OF THE DORSAL ROOT NEUROBLAST OF THE RABBIT EMBRYO

The centrally directed neurite of the dorsal root neuroblast has been described from the period of its initial entrance into the neural tube until a well-defined dorsal root is formed. Large numbers of microtubules, channels of agranular reticulum, and clusters of ribosomes are found throughout the length of the early axons. The filopodia of the growth cone appear as long thin processes or as broad flanges of cytoplasm having a finely filamentous matrix material and occasionally small ovoid or elongate vesicles. At first the varicosity is a small expansion of cytoplasm, usually containing channels of agranular reticulum and a few other organelles. The widely dilated cisternae of agranular reticulum frequently found within the growth cone probably correspond to the pinocytotic vacuoles seen in neurites in tissue culture. The varicosities enlarge to form bulbous masses of cytoplasm, which may measure up to 5 µ in width and 13 µ in length. They contain channels of agranular reticulum, microtubules, neurofilaments, mitochondria, heterogeneous dense bodies, and a few clusters of ribosomes. Large ovoid mitochondria having ribonucleoprotein particles in their matrix are common. Dense membrane specializations are found at the basal surface of the neuro-epithelial cell close to the area where the early neurites first enter the neural tube.     

THE ULTRASTRUCTURE AND HISTOCHEMISTRY OF THE SYNERGIDS OF COTTON

The composition and ultrastructure of the synergids of cotton were studied. The cells were found to be surrounded by a partial wall composed of cellulose, hemicellulose, and pectins. The structure of the wall was observed to consist of an unusual fibrillar arrangement. The filiform apparatus was demonstrated to be an extension of the wall at the micropylar end of the cell. Large amounts of ER surround the filiform apparatus. Also associated with the latter are large numbers of plastids and mitochondria. The nucleus is large and contains a single, large nucleolus and, frequently, 1 or more micronucleoli. The nuclear membrane contains membrane-bound vesicles but has few extensions into the cytoplasm. The ER is oriented parallel to the long axis of the cell and decreases in concentration from the micropylar to the chalazal end of the cell. Dictyosomes are common throughout the cell but are more numerous in the midportion where they are closely associated with the ER. The chalazal end of the cell is occupied by vacuoles rich in an inorganic compound which leaves a considerable residue of ash. Spherosome-like bodies are common throughout the cell. Both the plastids and mitochondria show evidence of division. Ribosomes are numerous and are both free and associated with the ER, nucleus, plastids, and mitochondria. The function of the synergids is proposed to be the absorption, storage, and transport of compounds from the nucellus. On the basis of this function, it is suggested that the synergids act by providing material to the egg and the developing embryo and endosperm and that they are involved in the growth of the pollen tube into the embryo sac.     

东方杯叶吸虫体被的超微结构

扫描电镜显示东方杯叶吸虫体被有许多族生棘,具纤毛乳突和无纤毛窝状乳突,附着器皮层特化为微毛。透射电镜观察表明,皮层是由合胞体、基膜和肌肉层组成,合胞体通过细胞通道与皮层细胞相连。文中详细描述了这些结构,揭示无纤毛窝状乳突为腺乳突,皮层细胞间存在线粒体细胞和附着器皮层形成微毛,探讨了这些结构的生理功能。体外培养成虫皮层结构的某些不正常变化,如皮层细胞的空虚松散,可作为评价吸虫体外培养的一种指标。     

桃小食心虫复眼的外部形态及结构特征*

桃小食心虫(Carposina nipponensis Wals)蛾复眼的外部形态与棉铃虫(Heliothis armi-gera Hubner)蛾等较相似,但大小及结构明显不同,它的体长为o.54毫米,宽为o.50毫米,每只复眼大约有l500个小眼组成。 小眼密度为每平方毫米3301个。透明区占小眼总长的64%。网膜细胞多在远端膨大,细胞核也大都在此集中。本文对小眼及其周围分10个层次进行了描述和摄影。     

Ultrastructure and phylogeny of the spermatozoid ofChara vulgaris (Charophyceae)

At maturity, spermatozoids of the green algaChara vulgaris are biflagellated, contain little cytoplasm, and coil for approximately 2 1/2 gyres within the mother cell wall. The anterior of the cell contains an ovoid headpiece anchoring two slightly staggered basal bodies that are positioned above and directly in front of approximately 30 linearly arranged mitochondria. An elongated stellate pattern occupies the transition zone between the BBs and axonemes. Flagella emerge from the cell just in front of the nucleus and encircle the full length of the spermatozoid. The spline comprises a maximum of 38 microtubules surrounding the anterior mitochondria and gradually decreases posteriorly to a minimum of 11. The dense nucleus is narrow, cylindrical, and occupies the central revolution of the cell. Six starch-laden plastids and associated mitochondria are linearly arranged at the cell posterior. Phylogenetic analyses of charalean taxa and archegoniates based on spermatogenesis strongly support the orderCharales, withNitella as the sister group toChara. Diagnostic features ofChara spermatozoids include absence of a lamellar strip and axonemes embedded in the cell for almost the entire length of the anterior mitochondria. Potential relationships amongCharales, Coleochaetales and archegoniates are evaluated in regards to the probable course of evolution of streamlined biflagellated gametes.     

FINE STRUCTURE OF THE NEUROHYPOPHYSIS OF THE OPOSSUM (DIDELPHIS VIRGINIANA)

The neurohypophysis of the opossum (Didelphis virginiana) was studied by electron microscopy in order to amplify Bodian''s classic light microscopic observations in which he demonstrated a definite lobular pattern. The lobule of the opossum neurohypophysis is divided into three regions: a hilar, a palisade, and a septal zone. The hilar portion contains bundles of nerve fibers, the extensions of the hypothalamo-hypophyseal tract containing neurofilaments but few neurosecretory granules. In the opossum, pituicytes have a densely fibrillar cytoplasm. Herring bodies are prominent in the hilar region. They are large bodies packed with neurosecretory granules that have been described as end bulb formations of axons. From the hilar region, axons fan out into a palisade zone where the nerve terminals packed with neurosecretory granules, mitochondria, and microvesicles abut upon basement membranes. The neurosecretory granules are similar to those present in the neurohypophysis of other mammals, except for an occasional huge granule of distinctive type. Material morphologically and histochemically resembling glycogen occurs as scattered particles and as aggregates within nerve fibers. The septal zone, containing collagen, fibroblasts, and numerous small capillaries, is separated from the adjacent glandular tissue by a basement membrane.     

THE FINE STRUCTURE OF THE LATERAL VESTIBULAR NUCLEUS IN THE RAT : I. Neurons and Neuroglial Cells

The lateral vestibular nucleus consists of multipolar isodendritic neurons of various sizes The distal segments of some dendrites display broad expansions packed with slender mitochondria and glycogen particles. These distinctive formations are interpreted as being growing tips of dendrites, and the suggestion is advanced that they are manifestations of architectonic plasticity in the mature central nervous system. Unlike large neurons elsewhere, the giant cells (Deiters) contain small Nissl bodies interconnected in a dense mesh-work. The Nissl substance is characterized by randomly arranged cisterns of the endoplasmic reticulum and by a high proportion of free ribosomes. Whether attached or free, ribosomes usually cluster in groups of four to six, and larger polysomal arrays are rare. Free ribosomal clusters also occur in the axon hillock and the initial segment. The neuronal perikarya contain distinctive inclusions consisting of a ball of neurofilaments enveloped by a complex honeycombed membrane. The failure of these fibrillary inclusions to stain with silver suggests that the putative argyrophilia of neurofilaments may reside in an inconstant matrix surrounding them. Giant cells of Deiters are in intimate contact with two kinds of cellular elements—astroglial processes and synaptic terminals. Oligodendroglial cells are only rarely satellites of giant cells; in contrast, they are frequently satellites of small and medium-sized cells.     

离体培养鼠疟原虫动合子形成过程的电子显微镜观察

本文报道了用透射电子显微镜观察离体培养的鼠疟原虫配子体到动合子的发育过程。 鼠疟原虫配子的发生是由嗜锇小体趋向配子体表面开始。雌配子体从红细胞中逸出后,嗜锇小体消失。雄配子体微管形成和鞭毛轴丝集合是从红细胞中逸出前出现的。合子转变为动合子由致密内膜及膜下微管形成时开始,继之形成顶端复合物,随着突起增大,表膜复合物逐渐向后延伸,最后包绕整个虫体,即完成动合子的发育。疟原虫生活史第一次核分裂可能发生在动合子形成期间。本文证实了离体培养的动合子与蚊体内发育的动合子结构相同。