The fine structure of the secretory cells of the uterus (shell gland) of the chicken

The secretory processes in the shell gland of laying chickens were the subject of this study. Three cell types contribute secretory material to the forming egg: ciliated and non-ciliated columnar cells of the uterine surface epithelium, and cells of tubular glands in the mucosa. The ciliated cells as well as the non-ciliated cells have microvilli, which undergo changes in form and extent during the secretory cycle. At the final stages of shell formation they resemble stereocilia. It is postulated that the microvilli of both cells are active in the production of the cuticle of the shell. The ciliated cell which has both cilia and microvilli manufactures secretory granules which arise from the Golgi complex in varying amounts throughout the egg laying cycle. Granule production reaches its greatest intensity during the early stages of shell deposition. The ciliated cell probably supplies proteinaceous material to the matrix of the forming egg shell. The non-ciliated cell has only microvilli. Secretory granules, containing an acid mucopolysaccharide, arise from the Golgi complex. Some granules are extruded into the uterine lumen where they supply the egg shell with organic matrix. Others migrate towards the supranuclear zone. Here a number of them disintegrate. This is accompanied by the formation of a large membraneless space, which is termed “vacuoloid.” Subsequently the vacuoloid regresses and during regression an extensive rough endoplasmic reticulum with numerous polyribosomes of spiral configuration appears. It is suggested that material in the vacuoloid originating from the disintegrating granules is resynthesized and utilized for the formation of secretory product. The uterine tubular gland cells have irregular, frondlike microvilli. During egg shell deposition, these microvilli form large blebs and are probably related to the elaboration of a watery, calcium-containing fluid.     

The ultrastructure of the cuticle of some British lumbricids (Annelida)

The ultrastructure of the cuticle of 11 species of British lumbricids is described. The number of unbanded collagenous fibre layers varies with the species and is roughly proportional to the size of the adult worm. Four zones are discernible in the cuticle matrix in all species except E. foetida where the outermost zone shows subdivision.
Microvilli, cytoplasmic extensions from the epithelial surface, occur. The "long" and "short" microvilli of other workers are shown to be different views of the same structure. The microvilli have an ovoid base with the two poles forming low shoulders on either side of the ascending microvillus. The bases are oriented at right-angles to the longitudinal axis of the worm and the microvilli are arranged in regular staggered rows along the same axis. Details of the spatial alignment of the microvilli are given and the possible role of these regularly arranged structures as factors in the orientation of the collagen fibre unit filaments is discussed, and it is speculated that they might also have some proprioceptive function.
Distally the microvilli terminate among the surface epicuticular projections and are shown to give rise to them. The epicuticular projections are peanut-shell shaped with a distinct substructure consisting of a 8 nm electron dense lining and two parallel dense discs, each 8 nm deep, above the "waist".
The mucous cell pores are lined with electron pale microfibrillar material and at the base of the pore a circlet of 13–15 short microvilli, with prominent tonofilaments, arises from the cytoplasm of the mucous cell. Surrounding the pore microvilli are numerous, small, membrane bound mucous pore particles.     

Ejaculatory duct of the migratory grasshopper,Melanoplus sanguinipes (fabr.) (Orthoptera : Acrididae): A histological and ultrastructural analysis

The ejaculatory duct of the migratory grasshopper (Melanoplus sanguinipes [Fabr.]) (Orthoptera : Acrididae) is divisible into 3 regions: upper ejaculatory duct (UED) into whose anterior end the accessory glands and vasa deferentia empty; the funnel characterized by its slit-like lumen; and the lower ejaculatory duct (LED). Anteriorly, the UED has a keyhole-shaped lumen surrounded by a thin intima and highly columnar epithelial cells whose most conspicuous feature is massive aggregations of microtubules. More posteriorly, the UED lumen differentiates into dorsal and ventral chambers, the former having a thick cuticular lining armed with spines. In the hindmost part of the UED, the ventral chamber expands to obliterate the dorsal chamber; its cuticular lining thickens, and conspicuous lateral evaginations develop. The thick cuticle includes 3 distinct layers and on its surface carries numerous spatulate processes. In this region, the epithelial cells develop numerous short microvilli beneath which are many mitochondria. As the funnel is reached, the intima becomes extremely thick, and the epithelial cells lack microvilli and most microtubules. Within the funnel, a new, very distinct form of cuticle appears, which is in “units”, each associated with an epithelial cell and having a rounded epicuticular cap. The new cuticle arises ventrally but rapidly spreads to encircle the entire lumen, at which point the LED is considered to begin. Beneath this new cuticle, the epithelial cells are columnar, have long microvilli, numerous mitochondria in the apical cytoplasm, and rough endoplasmic reticulum basally. Apically, adjacent cells are tightly apposed; however, prominent intercellular channels develop more basally. The ejaculatory duct's features are briefly discussed in terms of its role in spermatophore formation.     

Analysis of possible mechanisms of orthonectid emergence from their hosts

In the present study authors claim that the adult orthonectids can not move through host tissues by themselves. In various species of these enigmatic parasites there are at least two different mechanisms of emission of males and females from the host body. Intoshia linei, the orthonectid from Lineus ruber (Heteronemertini), and Intoshia variabili, the parasite of a flatworm Macrorhynchus crocea, realize the first way of emission. The plasmodium of these species forms tube-like outgrowths, which pierce the host tissues reaching the host body surface. The cytoplasm structure of these outgrowths differs from the cytoplasm of the central mass of plasmodium. Small mitochondria with electron dense matrix, lipid granules and vesicular bodies being common in the central part are absent in these outgrowths. Plasmodial outgrowths reach the host body surface and adult orthonectids move inside them using their cilia and stopping from time to time. The plasmodial outgrowths penetrate the ciliated epithelium, then males and females leave the host. Duration of emission may vary in different species from 6 to 13 days. The second mechanisms of emission is common for the orthonectid parasites of mollusks. Our observations of Rhopalura philinae from the gastropod Philine scabra lead to the conclusion that males and females leave their host practically simultaneously. When the plasmodium attains the terminal stage of its development most of the host entrails are already displaced by plasmodial mass. It causes breaks in host body walls and hence to emission of sexual individuals. During this process, which lasts about 24 hours, the mollusk dies. The same mechanism was observed in Rhopalura littoralis--parasite of the gastropod Onoba aculeus. Our investigations of emission ways reveal that the plasmodium of orthonectids has a potency of directing growth and can form certain structures. The process of forming the plasmodial outgrowths is coordinated in time and space. These outgrowths have certain directions inside the host body and the maturation of sexual individuals is clear related with the development of plasmodium outgrowth system. Our results suggest that forming of plasmodial outgrowths is an element of development of the united and highly integrated system. It is necessary to emphasize the capability of plasmodium to accomplish such morphogenetic transformations. This fact argues that plasmodium is a part of parasite organism and not host cells modified, like some experts supposed.     

Embryonic development of the jumping bristletail Pedetonutus unimaculatus Machida,with special reference to embryonic membranes (Hexapoda: Microcoryphia,Machilidae)

In the machilid Pedetonutus unimaculatus, a germ disc is formed by the aggregation and proliferation of cells within a broadly defined embryonic area. Cells adjacent to the embryonic area form the serosal fold that grows beneath the embryo. Then the embryonic margin is extended to form a cell layer or amnion that lies between the embryo and serosal fold. Thus, an amnioserosal fold is formed by the addition of the amnion to the serosal fold. Serosal cells cover the entire surface of the egg and begin to secrete a serosal cuticle. Soon the amnioserosal fold is withdrawn, and the embryo is exposed to the egg surface. The spreading amnion replaces the serosal cells that finally degenerate through the formation of a secondary dorsal organ. In the areas of amnion anterior and lateral to the embryo, yolk folds form and encompass the embryo. The amnion is a provisional dorsal closure and never participates in the formation of the definitive one. The amnioserosal fold of the Microcoryphia appears to have the functional role of secreting a serosal cuticle beneath the embryo. This fold of the Microcoryphia may be regarded as an ancestral form of the amnioserosal folds of the Thysanura-Pterygota. the yolk folds may appear to be passive transformation of the yolk mass linked to positioning of the growing embryo within the egg. There is no evidence that the yolk folds and the cavity appearing between them in the Microcoryphia are homologous to the amnioserosal fold and amniotic cavity in the Thysanura-Pterygota. The yolk folds appear to be one of the embryological autapomorphies in the Microcoryphia. © 1994 Wiley-Liss, Inc.     

Actin filaments, stereocilia and hair cells of the bird cochlea. VI. How the number and arrangement of stereocilia are determined.

Beginning in 8-day embryos, stereocilia sprout from the apical surface of hair cells apparently at random. As the embryo continues to develop, the number of stereocilia increases. By 10 1/2 days the number is approximately the same as that encountered extending from mature hair cells at the same relative positions in the adult cochlea. Surprisingly, over the next 2-3 days the number of stereocilia continues to increase so that hair cells in a 12-day embryo have 1 1/2 to 2 times as many stereocilia as in adult hair cells. In short, there is an overshoot in stereociliary number. During the same period in which stereocilia are formed (9-12 days) the apical surface of each hair cell is filled with closely packed stereocilia; thus the surface area is proportional to the number of stereocilia present per hair cell, as if these features were coupled. The staircase begins to form in a 10-day embryo, with what will be the tallest row beginning to elongate first and gradually row after row begins to elongate by incorporation of stereocilia at the foot of the staircase. Extracellular connections or tip linkages appear as the stereocilia become incorporated into the staircase. After a diminutive staircase has formed, eg. in a 12-day embryo, the remaining stereocilia located at the foot of the staircase begin to be reabsorbed, a process that occurs during the next few days. We conclude that the hair cell determines the number of stereocilia to form by filling up the available apical surface area with stereocilia and then, by cropping back those that are not stabilized by extracellular linkages, arrives at the appropriate number. Furthermore, the stereociliary pattern, which changes from having a round cross-sectional profile to a rectangular one, is generated by these same linkages which lock the stereocilia into a precise pattern. As this pattern is established, we envision that the stereocilia flow over the apical surface until frozen in place by the formation of the cuticular plate in the apical cell cytoplasm.     

A light and electron microscopic study of sporulation in the myxomyceteStemonitis virginiensis

Summary The conversion of the plasmodium ofS. virginiensis into sporophores has been examined at both the light and electron microscopic levels. Particular attention has been paid to stalk and columella formation, capillitial formation, nuclear behavior during sporulation and spore formation. Both the stalk and columella are formed within the sporangial initial as intraprotoplasmic secretions. A portion of the capillitium arises directly from the columella while the remainder forms within an anastomosing system of tubular vacuoles. As spore cleavage begins the nuclei within the sporangium begin to divide mitotically. The protoplasmic content of the sporangium is first divided into small protospores which typically contain a single dividing nucleus. Following the completion of mitosis each of these segments cleaves into yet smaller segments which develop into spores. Meiosis occurs in the spores some 12–16 hours after cleavage.     

ULTRASTRUCTURAL STUDY ON THE ATTACHING FILAMENTS AND VILLI OF THE OOCYTE OF ORYZIAS LATIPES DURING OOGENESIS

The formation of the attaching filaments and villi on the surface of the oocyte of Oryzias latipes were studied electron-microscopically. The oocyte at the early stage has almost smooth surface with a few tufts of microvilli. Some parts of the surface of the oocyte are in contact with the follicle cell, and these parts subsequently become protrusions. As maturation proceeds, a mass of fine granules appears in the space between the protrusion and the follicle cell. Similar granules begin to appear also in the space between the microvilli. These granules later become the outer layer of the chorion. The protrusions are reduced in height, and consequently become almost flat. At the same time, there appears some amorphous material of high electron density on the above-mentioned granules on the flat part. A bundle of parallel microtubules is formed in the material. The tubule is 180–200 A in diameter, and its wall consists of 12 or 13 subunits. The bundle increases in volume, and becomes the attaching filament or villus.     

云南松雌雄配子体的发育

云南松(Pinus yunnanensis Fr.)雄配子体于10月在小孢子叶腹面产生二个小孢子囊,内有许多进行分裂的造孢组织细胞。第二年一月下旬至二月初小孢子母细胞进行减数分裂。在分裂期间,细胞内所贮存的淀粉粒的分布发生变化。二月初四分体小孢子形成,绒毡层细胞解体。二日中旬单核花粉粒形成,外壁扩展形成二个异极对称的气囊。三月花粉在四细胞时期散发。 雌配子体于二月上旬在珠心皮下分化出孢原细胞。二月下旬大孢子母细胞进入减数分裂期。三月初直列四分体大孢子形成,珠孔端三个退化,合点端一个功能大孢子进入有丝分裂期,形成约32个游离核的配子体。次年三月初雌配子体形成,四月初中央细胞核分裂,四月底颈卵器成熟,卵核周围产生辐射状原生质纤丝。五月初受精开始。云南松雌雄配子体的发育与亚热带分布的P.roburghii相似。     

Ultrastructural location of calcium and magnesium during mineralisation of the cuticle of the shore crab,as determined by the K-pyroantimonate method and X-ray microanalysis

We have investigated the distribution of Ca²⁺ and Mg²⁺ in the new cuticle of moulting shore crabs (Carcinus maenas), using the K-pyroantimonate method in combination with X-ray microanalysis in order to identify antimony precipitates. During the premoult period, Ca²⁺ and Mg²⁺ accumulate in well-defined sites of the new pigmented layer. After moulting, mineralisation appears to begin preferntially at these sites. These form a honeycomb-like structure that quickly increases the rigidity of the new cuticle, with a small recruitment of material from extraneous sources. Mineralisation of the principal layer, on the other hand, immediately follows deposition of the organic matrix. Our experiments also provide evidence that the epidermal cell extensions associated with the pore canals are the means by which Ca²⁺ and Mg²⁺ are transferred from the epidermis into the mineralising cuticular layers. The plasma membrane of these cell extensions appears densely lined by particles of antimony precipitate that probably mark the location of the transporting sites. Shortly after moulting, the distribution of mineral deposits is such that the cell extensions cross the mineralised lamellae of the principal layer and constitute preferential access routes to the pigmented layer, where mineralisation is still in progress.     

Nuclei in the plasmodium of Intoshia variabili (Orthonectida) as revealed by DAPI staining

DAPI staining of wholeamounts was used to reveal the parasitic plasmodium of the orthonectid Intoshia variabili in its host, the turbellarian Macrorhynchus crocea. The nuclei of the parasite differ drastically from those of the host in size, morphology, and the estimated DNA content. Our findings indirectly support the idea that the orthonectid plasmodium is a distinct parasitic organism, rather than modified host cells.     

Fine structure of the developing gastric epithelium of the chick

The fine structure of the developing gizzard of the chick embryo has been studied to define the sequence of events in cytodifferentiation of the epithelium and to look for morphological evidence of epithelio-mesenchymal interaction. During the fourth day of incubation epithelial cells begin to form mucous secretory granules, later massive glycogen deposits appear, and finally by day 8 numerous cell processes have formed. Tissue was prepared by a number of methods to stain material associated with cell surfaces. At the time induction is presumbably occurring such stainable material is abundant. Epithelial and mesenchymal tissue components when cultured transfilter show no inductive effects and stainable cell surface material is greatly reduced near the epithelium.     

Ultrastructural study of midgut embryonic cytodifferentiation in the phasmid Clitumnus extradentatus Br.

The embryonic cytodifferentiation of Clitumnus midgut occurs very late when compared to that of other tissues in the embryo. It proceeds from hemolymph towards the yolk, first at the level of the muscular–connective tissue sheath, by the appearance of myofilaments in external–then internal–muscle fibers. In the gut epithelium, cytodifferentiation begins with the appearance of infoldings of the basal membranes of the cells. Then, microvilli and continuous junctions form at the apices of the cells. Microvilli appear in crypts, which seem to represent localized dilatations of intercellular spaces. At the level of these crypts, continuous junctions are formed somewhat later than are microvilli. This midgut differentiation coincides with deposition of the third embryonic (first larval) cuticle, and with a high titer of ecdysteroids.     

The electron microscopy of the human hair follicle. II. The hair cuticle

1. During the early differentiation of the cuticle the cell membranes smooth out and the cells become closely attached over most of their surface. The change seems to be due to a layer of cement which forms between them. The plasma membranes also increase in density. 2. The decreased membrane activity of the cuticle cells may prevent a phagocytosis of the melanocyte processes and thus account for the non-pigmentation of the cuticle. 3. The flattening and imbrication of the cuticle may possibly be explained by a zipper-like spread of cell contacts. 4. Keratinisation of the cuticle occurs at a late stage in its development; the keratin formed is an amorphous type, similar to the gamma-fraction of the cortex which is produced at a similar level. 5. Keratinisation is accompanied by the formation of complex intercellular layers similar to structures observed in the inner root sheath (see Part 3). 6. In the final stage of keratinisation the remaining cytoplasm condenses with the result that the cell is divided into a laminated structure with an outer keratinised layer and an inner layer, which is insoluble in keratinolytic solvents.     

Cytochalasins distinguish by their action resting human T lymphocytes from activated T-cell blasts

In the majority of resting human peripheral T lymphocytes obtained from separate individuals cytochalasin B (CB) and D (CD) cause a disappearance of microvilli and induce a rapid formation of prominent sac and bleb-like projections with a length of 1–10 μm randomly distributed over the cell surface. During mitogen stimulation the cells lose the tendency to develop such projections when subsequently exposed to CB and CD. By contrast, in activated T lymphocytes the cytochalasins provoke an asymmetric localization of microvilli including cell surface antigens and actin to a prominent protuberance often separated from the cell body by a constriction. This protuberance is distinct from conventional spontaneous uropods formed by conA-stimulated lymphocytes in relation to contact with other cells and with non-cellular surfaces. The cytochalasins therefore in their action distinguish resting small lymphocytes from activated T-cell blasts.     

Fine structure and morphogenesis of the sclerite epicuticle in the Atlantic shore crab Carcinus maenas

Three basic sublayers are identified in the epicuticle of the mineralised sclerites of the Atlantic shore crab Carcinus maenas (Crustacea, Decapoda): the surface coat, the cuticulin layer, and the inner epicuticle. Their morphogenesis and subsequent changes are described throughout the moulting cycle in the normal cuticle and the cuticular structures, namely the sensory bristles and epicuticular spines. At first, the cuticulin layer begins to form just after apolysis. This layer is built directly over the plasma membrane and immediately appears as a membrane-like structure 40 nm thick, composed of five symmetrically arranged laminae: two inner electron-lucent leaflets sandwiched between two thick electron-dense leaflets and separated by a thin dense median stratum. Elaboration of the inner epicuticle below the cuticulin layer is thought to occur via an intussusceptive process involving the pore canal cell extensions as transport routes. The inner epicuticle is made of vertically oriented microfibres embedded in an electron-dense matrix material. During the second half of the premoult period, the surface coat is deposited on the upper side of the cuticulin layer.     

Ultrafine structure of the integument of the tick Hyalomma asiaticum P. Sch. et E. Schl. in starvation and feeding]

Integument fine structure of H. asiaticum nymphs during their feeding and starvation has been studied. In hungry nymphs hypoderma has an ultrastructure typical for hypodermal cells of arthropods in the intermoulting period and is characterized by a poor development of granular endoplasmic reticulum, small number of mitochondrial and absence of Golgi complexes. The apical surface of the cells is covered with short irregularly scattered microvilli. The cuticle consists of the procuticle, which has a homogenous fine-granular structure, and four-layered epicuticle. During the feeding period hypodermal cells greatly increase in volume and the elements of granular endoplasmic reticulum and metachondria increase in number. Golgi complexes and a variety of apical vesicles have been observed. The number of microvilli on the apical surface increases that is accompanied by a cuticle growth. Procuticle, which is being formed within this period, has a lamellar structure.     

THE ELECTRON MICROSCOPY OF THE HUMAN HAIR FOLLICLE : PART 2. THE HAIR CUTICLE

1. During the early differentiation of the cuticle the cell membranes smooth out and the cells become closely attached over most of their surface. The change seems to be due to a layer of cement which forms between them. The plasma membranes also increase in density. 2. The decreased membrane activity of the cuticle cells may prevent a phagocytosis of the melanocyte processes and thus account for the non-pigmentation of the cuticle. 3. The flattening and imbrication of the cuticle may possibly be explained by a zipper-like spread of cell contacts. 4. Keratinisation of the cuticle occurs at a late stage in its development; the keratin formed is an amorphous type, similar to the γ-fraction of the cortex which is produced at a similar level. 5. Keratinisation is accompanied by the formation of complex intercellular layers similar to structures observed in the inner root sheath (see Part 3). 6. In the final stage of keratinisation the remaining cytoplasm condenses with the result that the cell is divided into a laminated structure with an outer keratinised layer and an inner layer, which is insoluble in keratinolytic solvents.     

FACTORS CONTROLLING THE REASSEMBLY OF THE MICROVILLOUS BORDER OF THE SMALL INTESTINE OF THE SALAMANDER

Hydrostatic pressure, when applied to segments of the small intestine of the salamander, causes a tremendous reduction in number of microvilli and a loss of the terminal web. The intestinal epithelium strips off from its deeper layers at the level of the basement membrane. When the pressure is released and this epithelial sheet is allowed to recover, the microvilli and its terminal web reappear. Stages in the reformation of microvilli are described. In the earliest stages, foci of dense material seem to associate with the cytoplasmic surface of the apical plasma membrane. From this material, filaments appear and their regrowth is correlated with the extension of the microvilli. We suggest that the dense material nucleates the assembly of the filaments which, in turn, appear instrumental in the redevelopment of microvilli. This concept is supported by the existing literature. Further, since neither the microvilli nor the terminal web reappear on any surface but the apical surface, even though the apical and basal surfaces are bathed with the same medium, we suggest that information in the membrane itself or directly associated with the membrane dictates the distribution of the dense material which leads to the formation of the microvilli and ultimately to the polarity of the cell.     

Fine Structure of the ‘Slit Organs’ of the Pycnogonid Anoplodactylus petiolatus (Anoplodactylidae)

Abstract The ‘slit organs’ of Anoplodactylus petiolatus are found all over the body cuticle. They are composed of a cuticular pore apparatus, an inner and an outer canal cell, and of four large and one to three small compartment cells. Plasma of the latter seven cells is almost completely filled with large membrane-enclosed compartments that contain either numerous small vesicles (one of the large cells) or homogeneous material of varying electron density (three large and all the small cells). Microvilli are found in the apical region of the compartment cells. The nucleus is situated basally where Golgi-cisternae, coated vesicles and free ribosomes are frequently found. Apical microvilli and vesicles are also formed by the inner canal cell indicating that it might directly be involved in transport. Anatomically the ‘slit organs’ are similar to class III glands described for many arthropods. In addition, discharge of secretion via large intracellular compartments is also a feature found in arthropod glands. Although pycnogonids appear to take up substances across the cuticle, a genuine secretion rather than a more generalized transport function is suggested for the ‘slit organs’.