The structure of the egg-shell of Aspiculuris tetraptera Schulz (Nematoda: Oxyuroidea).

The egg of Aspiculuris tetraptera is an ellipsoid measuring 93 x 40 microns. The shell consists of 5 layers: the external uterine layer, internal uterine layer, vitelline layer, chitinous layer and the lipid layer. This nomenclature is based upon the formation and histochemistry of the shell layers. The internal uterine layer contains a system of interconnecting spaces, partly filled by uterine secretion, which open to the exterior of the egg via breaks in the external uterine layer. The surface of the egg is covered by a system of interconnecting grooves. Freeze-etching reveals that the internal uterine layer is open to the exterior via pores, which open into the grooves. Rod-shaped particles are also revealed in the external uterine layer. The operculum of the egg consists of a modification of the uterine and chitinous layers of the shell.     

Oogenesis and egg-shell formation in Aspiculuris tetraptera Schulz (Nematoda: Oxyuroidea).

The ovary of Aspiculuris tetraptera has a prominent terminal cap cell. This is considered to be part of the ovarian epithelium. Oogonia detach from the short rachis and increase in size from 6 to 60 microns; accumulating hyaline granules, shell granules and glycogen. The hyaline granules persist in the eff cytoplasm after shell formation has been completed and are considered to be lipoprotein yolk. The shell granules contribute to the non-chitin fraction of the chitinous layer. A classification of the cytoplasmic inclusions of the nematode oocyte is proposed. Upon fertilization a vitelline membrane is formed which constitutes the vitelline layer of the egg-shell. The chitinous layer is secreted in the perivitelline space, between the vitelline layer and the egg oolemma. Upon completion of chitinous layer synthesis, the egg cytoplasm contracts away from its inner surface. The material of the lipid layer is secreted at the surface of the egg cytoplasm and adheres to the inner surface of the chitinous layer. During secretion of the chitinous and lipid layers by the egg cytoplasm, the uterine cells secrete the unit membrane-like external uterine layer and the crystalline internal uterine layer. A complex system of interconnecting spaces develops in the internal uterine layer. This system is open to the exterior via breaks in the external uterine layer. There is no direct involvement of the uterine cells in the formation of this structure.     

The structure of the egg-shell of Porrocaecum ensicaudatum (Nematoda: Ascaridida)

Wharton D. A. 1979. The structure of the egg-shell of Porrocaecum enslcaudatum (Nematoda: Ascaridida). International Journal for Parasltology9: 127–131. The egg-shell of Porrocaecum ensicaudatum is oval with an opercular plug at either end. The shell consists of three layers: an inner lipid layer, a middle chitinous layer and an outer vitelline layer. The vitelline layer has strands of particulate material attached to its outer surface. The chitinous layer consists of 8.5 nrn fibrils which are made up of a chitin microfibril core surrounded by a protein coat. The fibrils are oriented randomly or in parallel, there being no indication of helicoidal architecture.The chitinous layer varies in thickness to form a pattern of interconnecting ridges on the surface of the egg. This pattern presumably increases the shell's structural strength.     

Ultrastructural studies on the nematode Xiphinema diversicaudatum: Egg shell formation

The ultrastructure of the formation of the egg shell in the longidorid nematode Xiphinema diversicaudatum is described. Upon fertilization a vitelline membrane, which constitutes the vitelline layer of the egg shell, is formed. The chitinous layer is secreted in the perivitelline space, between the vitelline layer and the egg cell membrane. On completion of the chitinous layer, the material of the lipid layer is extruded from the egg cytoplasm to the outer surface, through finger-like projections. Both chitinous and lipid layers are secreted by granules in the egg cytoplasm that disappear as the layers are completed. Chitinous and lipid layers are formed during the passage of the egg through the oviduct. The vitelline layer is enriched with secretions produced by the oviduct cells and then by phospholipids secreted by the cells of the pars dilatata oviductus. The inner uterine layer is also formed by deposition of secretory products apposed on the egg shell in the distal uterine region and Z-differentiation. In the proximal part of the uterus, the egg has a discontinuous electron-dense layer, the external uterine layer. Tangential sections between chitinous and uterine layers revealed the presence of holes, possibly egg pores, delimited by the two uterine layers.     

The structure of the egg-shell of gLobodera rostochiensis (Nematoda: Tylenchida)

Perry R. N., Wharton D. A. and Clarke A. J. 1982. The structure of the egg-shell of Globodera rostochiensis (Nematoda: Tyienchida). International Journal for Parasitology12: 481–485. The ultrastructure and histochemistry of the egg-shell of Globodera rostochiensis are described. The eggshell consists of an outer vitelline layer, a chitinous layer and an inner lipid layer. The vitelline layer is not unit membrane-like and has strands of particulate material attached to its outer surface. The chitinous layer is made up of fibres consisting of a chitin microfibril core, surrounded by a protein coat. The lipid layer contains lipoprotein membranes. These vary in number, the most commonly observed pattern being two or three membranes loosely associated with the inner surface of the egg-shell.     

Ultrastructural organization of hypodermis and formation of cuticle in pharate larva of Leptotrombidium orientale (Acariformes: Trombiculidae)

The ultrastructural organization of hypodermis and the process of cuticle deposition is described for the pharate larvae of a trombiculid mite, Leptotrombidium orientale, being under the egg-shell and prelarval covering. The thin single-layered hypodermis consists of flattened epithelial cells containing oval or stretched nuclei and smooth basal plasma membrane. The apical membrane forms short scarce microvilli participating in the cuticle deposition. First of all, upper layers of the epicuticle, such as cuticulin lamella, wax and cement layers, are formed above the microvilli with plasma membrane plaques. Cuticulin layer is seen smooth at the early steps of this process. Very soon, however, epicuticle starts to be curved and forms particular high and tightly packed ridges, whereas the surface of hypodermal cells remains flat. Then a thick layer of the protein epicuticle is deposited due to secretory activity of hypodermal cells. Nearly simultaneously the thick lamellar procuticle starts to form through the deposition of their microfibrils at the tips of microvilli of the apical plasma membrane. Procuticle, as such, remains flat, is situated beneath the epicuticular ridges and contains curved pore canals. Cup-like pores in the epicuticle provide augmentation of the protein epicuticle mass due to secretion of particular substances by cells and to their transportation through the pore canals towards these epicuticular pores. The very beginning of the larval cuticle formation apparently indicates the starting point of the larval stage in ontogenesis, even though it remains for some time enveloped by the prelarval covering or sometimes by the egg-shell. When all the processes of formation are over, hungry larvae with a fully formed cuticle are actively hatched from two splitted halves of prelarval covering.     

Morphology of dry-resistant eggs in parthenogenetic Heterocypris incongruens (Ramdohr, 1808) (Ostracoda, Crustacea)

It has been known that many organisms evolved to survive in temporary or ephemeral inland waters. Many of them have dry-resistant eggs against desiccation. The structural feature of egg shell is important because only this will ensure to survive the dry period. Structural features of egg shell in the parthenogenetic Heterocypris incongruens (Ramdohr, 1808) was investigated by scanning electron microscope. Results showed that egg shell structure consists of two distinct layers; an outer layer with holes or alveoli and an inner layer consisting of two dense sublayers. Also, structural similarities in egg-shell of H. incongruens and some other crustaceans which combat desiccation problem will be discussed.     

Egg envelopes of Streptocephalus dichotomus Baird: A structural and histochemical study

The origin, ultrastructure and histochemical properties of the egg membranes in the South Indian anostracan, Streptocephalus dichotomus have been studied. The egg morphology and the ultrastructure of the tertiary membrane of this phyllopod crustacean have been examined both by scanning and transmission electron microscopy. Scanning electron microscopic observations on the egg surface reveal the characteristic ridges on the egg surface with pores. Similarly, the tertiary egg shell of S. dichotomus consists of two distinct layers, an outer cortex and an inner alveolar layer. There are specific differences in the structure and in the relationship of one layer to the other. The alveolar layer is characterised by large lipid droplets and an alveolar mesh. These two layers termed as tertiary layers are secreted by maternal shell glands. The outer tertiary egg layers are phenolically tanned, the precursor materials for tanning being derived from shell gland secretions.     

The egg-shell of Labiostrongylus eugenii (nematoda,strongyloidea): Structure and function

The egg-shell of Labio-strongylus eugenii consists of three layers; an outer vitelline layer, a middle chitinous layer and an inner lipid layer. The presence of chitin and protein in the middle layer was demonstrated by the use of chitinase and differential staining. The lipid layer was found to be made up of two layers, the innermost having large globules on its outer face. The shell was found to be permeable to liquid water, as demonstrated by the penetration of vital dyes. Eggs were able to develop normally with little or no loss of volume during periods of moisture stress when either osmotic or suction pressures were applied. The survival of eggs, as measured by hatching success, over periods of time at a range of saturation deficits and osmotic pressures was measured, and compared with known survival rates for other nematode species. The problems of working with nematode species whose life cycles have not been established are discussed. Possible survival strategies for Australian strongylids during periods of moisture stress are outlined.     

Observations on the morphology of Toxocara pteropodis eggs

Fertile eggs of Toxocara pteropodis, passed in the faeces of juvenile flying-foxes, were ovoid to spheroid in shape with a diameter range of 80-110 microns. The shell was often seen to comprise 4 layers: a fine inner lipid layer, a thicker clear chitinous layer, an equally thick outer vitelline layer and a pitted outermost, proteinaceous uterine layer of variable thickness. Infertile eggs were less uniform in shape and generally did not have well-defined shell layers, the formation of which is triggered by sperm penetration of the oocyte. The eggs of this species are bulkier than those of related ascaridoids, apparently because of a thicker external coat which, while not providing mechanical strength, is thought to protect against desiccation. Scanning electron microscopical findings suggest that the outer layer is not applied directly by uterine cells, but forms by the gradual deposition of secretions in the uterine lumen, regardless of whether the oocyte has been fertilized.     

Mosquito embryos and eggs: polarity and terminology of chorionic layers

The development of genetically modified vectors refractory to parasites is seen as a promising strategy in the future control of endemic diseases such as malaria. Nevertheless, knowledge of mosquito embryogenesis, a pre-requisite to the establishment of transgenic individuals, has been presently neglected. We have here studied the eggs from two neotropical malaria vectors. Eggs from Anopheles (Nyssorhynchus) albitarsis and Anopheles (Nyssorhynchus) aquasalis were analyzed by laser scanning microscopy and scanning electron microscopy and compared to those of Drosophila melanogaster. We verified basic conflicting data such as mosquito egg polarity and ultrastructure of eggshell layers. A 180 degrees rotation movement of the mosquito embryo along its longitudinal axis, a phenomenon not conserved among all Diptera, was confirmed. This early event is not taken into account by several present groups, leading to a non-consensual assignment of eggshell dorsal and ventral poles. Since embryo and egg polarities, defined during oogenesis, are the same, we propose to consider the flattened egg side as the dorsal one. The structure of Anopheles eggshell was also examined. Embryos are covered by a smooth endochorion or inner chorion layer. Outside this coat lies the compound exochorion or outer chorion layer, assembled by a thin basal lamellar layer and external tubercles. The terminology related to eggshell layers is discussed.     

Fine structure of the eggshell of Ommatissus binotatus Fieber (Homoptera,Auchenorrhyncha, Tropiduchidae)

The external morphology and fine structure of the eggshell of Ommatissus binotatus Fieber (Homoptera : Tropiduchidae) was investigated by light, scanning and transmission electron microscopy. The egg surface has 2 main regions: a specialized area and an unspecialized egg capsule. The specialized area is characterized by a large respiratory plate containing the operculum and a short respiratory horn. The latter consists of an external hollow tube and an internal coneshaped projection hosting a micropylar canal. The eggshell has 4 layers: the vitelline envelope, a wax layer, the chorion and an outer mucous layer. The chorion has inner, intermediate and outer parts. The functions of the different parts of the eggshell are discussed. Characters useful to define the eggs and the oviposition habit in the family Tropiduchidae were provided. The size and morphology of the egg, plate, respiratory horn and operculum are suggested as useful characters for ootaxonomic analysis.     

Studies of male sexual tubes in hermit crabs (crustacea, decapoda, anomura, paguroidea). I. Morphology of the sexual tube in Micropagurus acantholepis (Stimpson, 1858), with comments on function and evolution

The external morphology and internal structure of the male sexual tube of the hermit crab Micropagurus acantholepis, a member of the family Paguridae from Australian waters, is described in detail using histological thick sectioning and scanning and transmission electron microscopy techniques. This is the first in-depth study of a sexual tube in the Paguroidea, a group where a remarkable number of genera (55.9% in the family Paguridae) with species having these intriguing sexual structures are known. In M. acantholepis a sexual tube is present on the left side, whereas only a gonopore is present on the right side. The tube is used for the delivery of spermatophores to the female and consists of a sheath of cuticular origin surrounding an internal, functional extension of the posterior vas deferens. Pedunculate spermatophores were observed within the lumen and partially extruding from the terminal opening of the tube in preserved specimens. The tube protrudes from the left coxa of the fifth pereopod as an elongate 3-mm-long, hollow, coiled structure with a terminal opening. Exteriorly the tube consists of a conspicuous thick chitinous cuticular ridge throughout its length, and a thin chitinous cuticle with sparse, regularly arranged simple setae. Interior to the cuticle, the tube contains loose connective tissue, secretory cells, oblique muscle, circular muscle, and epithelial cells. The latter cells line a central lumen that runs the length of the sexual tube. The morphology, cellular composition, and function of the tube are discussed.     

Electron histochemistry and ultrastructural localization of carbohydrate-containing substances in the sheath of Volvox.

The location and characteristics of carbohydrate-containing structures within the intact sheath of Volvox were studied by 3,3'-diaminobenzidine tetrahydrochloride-osmium, colloidal iron, colloidal thorium, ruthenium red and periodic acid-silver methenamine staining. The sheath consists of external and internal fibrillar layers separated by a tripartite structure. The external layer reacts positively with 3,3'-diaminobenzidine tetrahydrochloride, colloidal iron, colloidal thorium and ruthenium red, indicating that it contains acid mucosaccharides. Staining in the external layer is abolished by Ba(OH)2 treatment. The tripartite structure and internal fibrillar layer contain periodic acid reactive groups which do not occur in the external layer. Under certain conditions, reactions between the cationic dyes and the internal material were also observed. It is postulated that the internal matrix of the sheath contains glycoproteins or a mixture of acid mucosaccharides and glycoproteins. Possible functions of the sheath material are discussed.     

Egg capsules of the dusky catshark Bythaelurus canescens (Carcharhiniformes,Scyliorhinidae) from the south‐eastern Pacific Ocean

The external morphology of the egg capsule of Bythaelurus canescens and its fixation to the substratum are described. Bythaelurus canescens egg capsules are typically vase‐shaped, dorso‐ventrally flattened, pale yellow in colour when fresh and covered by 12–15 longitudinal ridges. The anterior border of the capsule is straight, whereas the posterior border is semicircular. Two horns bearing long, coiled tendrils arise from the anterior and posterior ends of the capsule. The presence of longitudinal ridges and long coiled tendrils at both anterior and posterior ends of the capsule readily distinguish these egg capsules from those of other chondrichthyans occurring in the south‐east Pacific Ocean.     

Oogenesis and egg shell formation in Heterakis gallinarum (Nematoda)

The structure of the developing ova and egg shell formation of Heterakis gallinarum has been described. The oogonia are small, undifferentiated cells which are arranged around a central cytoplasmic rachis. The oogonia and young oocytes are in cytoplasmic continuity with the rachis and it is suggested that the rachis may influence synchronous development of the oocytes. The oocytes contain two types of granule; refringent, which give rise to the ascaroside layer of the egg shell, and another kind which appear to be a type of yolk for the developing egg. After fertilization the spermatozoon produces numerous ribosomes; a second unit membrane appears beneath the oolemma, and the chitinous layer of the shell forms between the oolemma and this inner membrane. The refringent granules later produce the ascaroside layer of the shell between the chitinous layer and the inner membrane. The outermost layer of the shell is produced from material secreted by the cells of the uterus.     

Heterodera glycines: eggshell ultrastructure and histochemical localization of chitinous components

The eggshell in most nematodes consists of an outer vitelline layer, a middle chitinous and an inner lipid layer. Earlier work with eggs of Heterodera glycines suggests the presence of two chitinous layers but the vitelline layer was not observed. From our observation the outer chitin layer described in past literature is actually a vitelline layer. Histochemical analysis has demonstrated that chitin is absent from the outer envelope. Electron microscope observations of the eggshell show a waxy appearance and osmium staining consistent with that of the proteinaceous vitelline layer found in other nematodes. Lectin localization also shows that the eggshell continues to develop past fertilization with the delivery and integration of eggshell precursors. Contrary to previous reports, we propose that the ultrastructure of the eggshell H. glycines follows the common three-layer structure observed in other nematodes.     

Rhigonema infecta (Leidy, 1849) Christie & Cobb, 1927 and the systematic position of the Rhigonematidae sensu Théodoridès, 1965

Summary Rhigonema infecta (Leidy, 1849) Christie & Cobb, 1927, a member of the family Rhigonematidae sensu Théodoridès, 1965, is redescribed from the diplopod Narceus annularis from Sharbot Lake and Long Point, Ontario, Canada. R. infecta is most similar to R. subtruncatum Dollfus, 1952 but differs from this species in possessing four rather than three post-cloacal papillae in the male. Rhigonematids have been affiliated with members of the order Oxyurida by most authors but study of R. infecta suggests that rhigonematids should be placed in their own order, the Rhigonematida. Members of the order Rhigonematida are characterized by: two spicules in the male; H-shaped excretory system; are round to oval sperms; thick and smooth egg-shell; apparently lacking a uterine layer; and development in the egg involving no moults and resulting in a long, thin, coiled larva. In contrast, oxyuridans have a single spicule, the excretory system is X-shaped, the sperm is comet-shaped and the egg-shell has a prominent striated uterine layer. Development in the egg involves at least one and probably two moults and results in a short, robust, uncoiled larva. ac]19810310     

Ultrastructural and histochemical studies of the egg capsules of Perla marginata (Panzer, 1799) and Dinocras cephalotes (Curtis, 1827) (Plecoptera : Perlidae)

Eggshells of stone flies P. marginata and D. cephalotes (Plecoptera : Perlidae), inhabiting mountain streams, were examined using scanning and transmission electron microscopes, a phase-contrast light microscope and histochemical methods to detect proteins, lipids and polysaccharides.The eggshells of the species investigated consist of a vitelline envelope, chorion and gelatinous sheet decorated on its outer surface with mushroom-like structures. An anchoring structure (attachment disc) is situated on the posterior pole of the egg. The structure and function of the attachment disc, as well as the possible taxonomic applications, are discussed. The morphology and histochemical composition of all these elements of the shell clearly demonstrate good adaptation to land and aquatic habitats; the chorion consists of 2 layers, the internal layer being finely perforated by numerous aeropyles. The external layer, with fewer, regularly placed aeropyles, protects the egg interior against dehydration in the land habitat. The gelatinous sheet seems to provide additional protection. Mushroom-like structures, situated on its surface, correspond with the positions of aeropylar openings. These and other interrelations between chorion structure and function are discussed.