The structure of the postantennal organ in Onychiurus sp. (Insecta: Collembola) and its connection to the central nervous system

Summary The postantennal organ in Onychiurus (group armatus) is a sensory organ comprising one sensory cell, several enveloping cells and cuticular structures.The perikaryon of the sensory cell is located in the central nervous system and distally gives off a dendrite in which one inner and two outer segments are distinguishable. Two ciliary structures connect the outer dendritic segments with the inner segment. The outer segments divide repeatedly, basal to the cuticular structures, into small branches which end distally beneath the cuticular wall. The wall of the cuticular structures is very thin and is pierced by numerous funnel-shaped pores. The pores are filled with electron-dense material which forms a continuous sheath underneath the cuticle. This material encases the small dendritic branches and the processes of the enveloping cells which occupy the lumen of the cuticular structures. There are three types of enveloping cells: one inner, several outer and one basal. Their processes differ in the manner in which they envelop the various regions of the dendrite.At the beginning of moulting outer dendritic branches are not found within the cuticular structures of the organ. They may be assumed to retract inwardly. However, in the later stages, when the cuticle is fully formed, the outer dendritic segments appear to divide. It is assumed that the small dendritic branches reach their targets before ecdysis. The electrondense material which clogs the intermoult cuticular pores is absent until the final stages of the moulting cycle.Supported by a grant from the Deutscher Akademischer Austauschdienst.     

Development of antennal sensilla during moulting inNeomysis integer (Leach) (Crustacea,Mysidacea)

Summary The sensilla are associated with 6 enveloping cells. The innermost enveloping cell (e 1) secretes the dendritic sheath (=thecogen cell). All other enveloping cells are involved in the formation of the outer cuticular apparatus in secreting the cuticle of a definite region of the new hair shaft.The development of the new sensilla begins when an exuvial space expands between old cuticle and epithelium. The newly forming hair shafts lie folded back in an invagination of the epidermal tissue. Only a distal shaft part projects into the free exuvial space. The cuticle of the distal and middle shaft region is secreted by the three middle enveloping cells (e 2–e 4) (=trichogen cells), which are arranged around the dendritic sheath.The wall of the cylinder, in which the distal shaft is situated, is formed by the cuticle of the future proximal shaft region. It is secreted by the outer enveloping cells (e 5 and e 6). Furthermore, both enveloping cells form the hair socket (=trichogen-tormogen cells).The outer dendritic segments encased within a dendritic sheath run up through the newly formed hair shaft and continue to the old cuticular apparatus. The connection between sensory cells and old hair shaft is maintained until ecdysis. On ecdysis the old cuticle is shed and the newly formed shaft of the sensillum is everted like the invaginated finger of a glove. The dendritic sheath and the outer dendritic segments break off at the tip of the new hair shaft. Morphologically this moulting process ensures that the sensitivity of the receptors is maintained until ecdysis.The internal organization of the sensory cells shows no striking changes during the moulting cycle. An increased number of vesicles is accumulated distally within the inner dendritic segments and distributed throughout the outer segments of the dendrites. The cytoplasmic feature of the enveloping cells indicates that synthesis and release of substances for the cuticular apparatus of the new sensillum take place.     

The ultrastructure of the salt gland of Spartina foliosa

Summary The salt gland in Spartina foliosa is composed of two cells, a large basal cell and a smaller, dome-shaped cap cell which is located on a neck-like protrusion of the basal cell. There is no cuticular layer separating the salt gland from the mesophyll tissue. The basal cell has dense cytoplasm which contains numerous mitochondria, rod-like wall protuberances, and infoldings of the plasmalemma which extend into the basal cell and partition the basal cell cytoplasm. The protuberances originate on the wall between the basal and the cap cells and are isolated from the basal-cell cytoplasm by the infoldings of the plasmalemma. While the cap cell has no partitioning membrane system or wall protuberances, it resembles the basal cell by having dense cytoplasm and numerous mitochondria.The basal cell seems to be designed for efficient movement of ions toward the cap cell. The long, dead-end extracellular channels in the basal cell of Spartina appear comparable to surface specializations seen in the secreting epithelium of animal cells which carry out solute-linked water transport. The number of mitochondria and their close association with the plasmalemma extensions suggest that they have an important role in the transfer of ions through the basal cell.The accumulated ions would move into the extracellular spaces along an osomotic gradient where the accompanying passive flow of water would move the ions into the cap-cell wall and from there the solution would pass out through the pores in the cuticle.     

Ultrastructure of a possible new type of crustacean cuticular strain receptor in Carcinus maenas (crustacea,decapoda)

A hitherto unknown sensillum type, the “intracuticular sensillum” was identified on the dactyls of the walking legs of the shore crab, Carcinus maenas. Each sensillum is innervated by two sensory cells with dendrites of “scolopidial” (type I) organization. The ciliary segment of the dendrite is 5–6 μm long and contains A-tubules with an electron-dense core and dynein arm-like protuberances; the terminal segment is characterized by densely packed microtubules. The outer dendritic segments pass through the endo- and exocuticle enclosed in a dendritic sheath and a cuticulax tube (canal), which is suspended inside a slit-shaped cavity by cuticular lamellae. The dendrites and the cavity terminate in a cupola-shaped invagination of the epicuticle. External cuticular structures are lacking. Three inner and four to six outer enveloping cells are associated with each intracuticular sensillum. The innermost enveloping cell contains a large scolopale that is connected to the ciliary rootlets inside the inner dendritic segments by desmosomes. Scolopale rods are present in enveloping cell 2. Since type I dendrites and a scolopale are regarded as modality-specific structures of mechanoreceptors, and since no supracuticular endorgan is present, the intracuticular sensilla likely are sensitive to cuticular strains. The intracuticular sensilla should be regarded as analogous to insect campaniform sensilla and arachnid slit sense organs.     

THE ULTRASTRUCTURE OF THE SALT GLANDS OF CYNODON AND DISTICHLIS (POACEAE)

The epidermal salt glands of the grasses Cynodon and Distichlis consist of a small outer cap cell and a large, flask-shaped basal cell. The wall of the basal cell is contiguous with those of the adjacent epidermal cells and underlying mesophyll cells. The basal cell is connected symplastically with all adjoining cells via plasmodesmata. The outer, protruding portion of the glands is covered by a cuticle continuous with that of the adjoining epidermal cells. However, the lateral cell walls of the glands are not incrusted by this cuticle. The cap cell wall has a loose, mottled appearance quite different from the compact striated appearance of the basal cell wall. The cap cell is characterized by dense cytoplasm containing many organelles and a varying number of small vacuoles. The basal cell cytoplasm is distinguished by the presence of an intricate system of paired membranes that are closely associated with mitochondria and microtubules. These membranes are infoldings of the plasmalemma that originate adjacent to the wall separating the cap and basal cells. The space enclosed by the paired membranes, therefore, is an extracellular channel that is open only in the direction of secretory flow. The consistent orientation of this system of paired membranes suggests that it represents a structural specialization which is directly and functionally involved in the secretory process. The close association of mitochondria and microtubules with the paired membranes implies that these structures are also functionally related to the secretory process. Finally, the results of this study indicate that these glands are ultrastructurally similar to those of Spartina and that the glands of these three grasses are structurally distinct from those of dicotyledonous plants.     

Morphology of the Salt Gland of Spartina anglica Hubbard

Apart from roots, rhizome, stem, the adaxial surfaces of the leaf sheaths and palea in the body of the plant of Spartina anglica, the salt glands are found in all other aerial parts, especially, they are abundant in lamina. The gland is composed of two differential cells, a big basal cell and a small, dome- shaped cap cell which is located on the neck-like protrusion of the basal cell. Both of the cap cell and the basal cell have dense cytoplasm, large nucleus, numerous mitoehondria and a few other organelles. The basal cell has wall protuberances, and infoldings of the partitioning membrane system which extend throughout the basal cell, and separate the basal cell cytoplasm. A dominant feature of the cap cell is the distinct compach, nueleolus and its chromatin distributed throughout the karyoplasm. In shoulder and bottom of the basal cell there is no cuticular layer separating them from the epidermal cell and mesophyll cells, but in the walls connceting the basal cell with the epidermal cells and cap cell there are pronounced plasmodesmata. It is possible that devolopment of the gland in Spartina anglica is the same as in S. townsendii, and that pathway of secretion is similar to both of S. foliosa and S. townsendii.     

Elektronenmikroskopische Untersuchungen anAnaitides mucosa (Annelida,Polychaeta). Cuticula und Cilien,Schleimzellen und Schleimextrusion

Two components, a basal cuticle and an epicuticle, make up the cuticle ofA. mucosa. The basal cuticle consists of collagen fibrils, which are arranged in about 20 layers. The orientation of the fibrils changes rectangularly from one layer to the next. Fine filaments interweave the basal cuticle. The epicuticle, which is covered by a layer of electron dense material, is composed of irregularly arranged thin filaments. Branched microvilli of the epidermal cells penetrate the cuticle. Bacteria are found in the basal cuticle. Dorsally each segment has a band of densely packed smooth cilia. Laterally and partly ventrally aggregates of cilia are observed. These cilia exhibit apically artificial swellings. At least six different mucous cells are observed in the epidermis, morphologically distinguishable by the structure of the secretion products. Mucus is secreted via exocytosis through cuticular pores. During this process the mucus might expand. The secreted mucus consists of filamentous subunits.     

Coordinated development in the fly foot: Sequential cuticle secretion

Development of the adult fly foot falls into clearly defined phases of cell division, growth, cuticle secretion and cell death. The pulvillus is composed dorsally of two giant cells and ventrally of thousands of minute tenent cells; the former produce the dorsal footpad cuticle and the latter the thousands of tenent hairs. Cell divisions are still occurring in future tenent cells when increase in size of the cells and in polyteny of the chromosomes is already occurring in the two dorsal cells. Also cell death occurs considerably earlier in the tenent cells, yet the sequential secretion of some six cuticular layers takes place at comparable times in dorsal and ventral cuticles. The cuticular layers formed are, in their order of secretion: ecdysial membrane, cuticulin of the epicuticle, dense exocuticle, homogeneous exocuticle, an intermediate layer, wax of the epicuticle, and an extensive mass of endocuticle. The ecdysial membrane seems to perform an important mechanical role in maintaining the shape of the delicate cytoplasmic projections of the tenent cells, before and during cuticle secretion, and in establishing the cuticular pattern of ridges in the dorsal cuticle. Comparisons are made with trichogen cell cuticle development and with tracheal cuticle. Tracheal, trichogen and dorsal footpad cuticle patterns are compared. Details of giant cell activity provide a working basis for studies of nuclear-cytoplasmic interactions, and the whole system raises many unsolved problems in the general field of cell differentiation and pattern formation.     

The ultrastructure of the female accessory gland,the cement gland,in the insect Rhodnius prolixus

The cement gland of Rhodnius prolixus is an epidermally derived tubular gland consisting of a distal synthetic region and a proximal muscular duct region. The synthetic region consists of numerous secretory units joined to a central chitinous duct via cuticular ductules. Proteinaceous secretion, synthesized by the goblet-shaped secretory cell, passes through the delicate cuticular lattice of a ductule-end apparatus and out through fine ductules to the central duct. Secretory cells are rich in rough endoplasmic reticulum and mitochondria. Light microscopy, SEM and TEM reveal the delicate lattice-like end apparatus structure, its formation and relationship to the secretory cell. The secretory cell associates via septate junctions with a tubular ductule cell that encloses a cuticle-lined ductule by forming an elaborate septate junction with itself. The ductules are continuous with the cuticle lining of the large central duct that conveys secretion to the proximal area. The proximal muscular duct has a corrugated cuticular lining, a thin epithelium rich in microtubules and thick longitudinal, striated muscles which contract during oviposition, forcing the secretion out. Histochemistry and electrophoresis reveal the secretion as proteinaceous.     

Femoral chordotonal organ in the legs of an insect,Chrysoperla carnea(Neuroptera)

The femoral chordotonal organ (FCO) inChrysoperla carneais situated in the distal part of the femur and consists of two scoloparia, which are fused at their distal end. The distal scoloparium contains 17-20 scolopidia, and the proximal one six scolopidia. Each scolopidium consists of two sensory cells and three types of enveloping cells (glial, scolopale and attachment cell). The sensory cells of different scolopidia do not lie at the same level in the FCO. Therefore the attachment cells of different scolopidia have different lengths. In the FCO, three types of ciliary roots are found in different sensory cells. The dendrite of the sensory cell terminates in a distal process, which has the structure of a modified cilium (9x2+0). The very distal part of the cilium is surrounded by an extracellular electron dense material, the cap, and ends in a terminal dilation. The scolopale cell contains the electron dense scolopale rods, consisting of plentiful microtubules. In their middle third the scolopale rods are fused and form the scolopale. In the FCO septate junctions, desmosomes and hemidesmosomes are found.     

Mechanical,sensory and glandular structures in the tarsal unguitractor apparatus of Chironomus riparius (Diptera,Chironomidae)

Summary The legs of chironomid midges from a laboratory colony were examined in the region of the joint between the fifth tarsal segment and the pretarsus, especially the surface of the unguitractor and the manner in which the unguitractor fits into a ventromedian groove in the edge of the tarsus when the joint is flexed. The region was reconstructed from serial sections to clarify the spatial relations of the internal structures to one another and to the external structures. Ultrastructural characteristics of the cells and cuticle suggest a secretory function of the unguitractor. An amphinematic scoloparium is suspended between the point at which the unguitractor attaches to its tendon and the transverse diaphragm within the tarsus. This mechanoreceptor could serve as a proprioceptive sensor of the position of unguitractor and tarsus; it could also be an exteroceptor, sensing vibration in the substrate and/or the air. In the context of functional morphology, the clamping of the unguitractor in the ventral hollow in the tarsus could have the effect of resetting the sensitivity of the sensor. On the other hand, this arrangement could also simply act as an energy-saving means of fixing the claws in the grasping position for long periods.Abbreviations aj adhering junction - bl basal labyrinth - bm basement membrane - cc cuticular cap - cd cellular diaphragm - cth cuticular thickening - dp matrix with dense particles - ec enveloping cells - f filaments - fot funnel-like opening of tendon - ic intracellular canaliculi - lp lateral process of ec - pAc process of A cell - pv pulvillus - r rootlets of cilia - sc scolopale cell - sco scoloparium - sd septate desmosomes - t tendon - tb tubular body - tu tubules - u unguis, or claw - upl unguitractor plate     

The ventral epithelium of Trichoplax adhaerens (Placozoa): Cytoskeletal structures,cell contacts and endocytosis

Summary All cilia emerge from ciliary pits supported along their circumference by 22–24 dense rodlets that are connected by filaments to a surrounding sheath of endoplasmic reticulum. The proximal part of the basal body is provided with two short lateral rootlets and one long terminal rootlet, all associated with microtubules. The lateral rootlets are in turn connected by fine fibrous material to the dense supporting rodlets which follow the contour of the ciliary pit and extend along the ciliary membrane beyond the level of the basal plate where the central pair of microtubules originates. The proximal part of the basal body has fine fibrous connections to the endoplasmic reticulum while its distal portion is surrounded by nine curved sheets. The terminal cell contactions are by belt desmosomes that are accompanied by a bundle of microfilaments which encircle the apical region of the cell and insert at the cell membrane. Tight junctions are lacking. Endocytosis was demonstrated by the uptake of cationized ferritin. The structures associated with the ciliary pits are probably associated with the firm anchorage of the ciliary base since Trichoplax adheres to the substrate as it moves propelled by its ventral cilia. The marginal bundle of microfilaments may be involved in folding of the organism during feeding.     

Ultrastructure of the tubular nephron of the lizard Podarcis (= Lacerta) Taurica

The proximal, intermediate, and distal convoluted tubules of the neprhon of Podarcis (= Lacerta) taurica were examined by electron microscopy. Proximal tubule cells have large, apical cytoplasmic protrusions and microvilli interpreted to function in urate secretion. Adjacent cells are bound apically by tight junctions and desmosomes but interdigitate in their basal region. This situation is repeated in the other tubules with significant differences in intercellular space width. The basal surfaces bear numerous cytoplasmic processes. The intermediate tubule has proximal and distal segments each with dark, ciliated, and light cells, the cuboidal dark cells with dense cytoplasm constituting the main bulk of the wall. As the cells of the proximal and distal segments resemble those of the proximal and distal convoluted tubules, respectively, the intermediate tubule is considered as a transition region. The ciliated cell body has two broad processes extending from the lumen, one to the basement membrane and one to a foot process of a light cell. The light cell is surrounded by dark and ciliated cells. It does not reach the lumen, but contacts the basement membrane through a process running below a ciliated cell to form a mushroom-shaped structure in tubule cross-section, the light cell process forming the stalk and a ciliated cell the cap. The cilia probably propel the glomerular filtrate towards the distal convoluted tubule. This latter tubule has initial, middle, and terminal zones, all nonciliated but with different lumen widths and cell shapes.     

THE FINE STRUCTURE OF COCKROACH CAMPANIFORM SENSILLA

Campaniform sensilla on cockroach legs provide a good model system for the study of mechanoreceptive sensory transduction. This paper describes the structure of campaniform sensilla on the cockroach tibia as revealed by light- and electron-microscopy. Campaniform sensilla are proprioceptive mechanoreceptors associated with the exoskeleton. The function of each sensillum centers around a single primary sense cell, a large bipolar neuron whose 40 µ-wide cell body is available for electrophysiological investigation with intracellular microelectrodes. Its axon travels to the central nervous system; its dendrite gives rise to a modified cilium which is associated with the cuticle. The tip of the 20 µ-long dendrite contains a basal body, from which arises a 9 + 0 connecting cilium. This cilium passes through a canal in the cuticle, and expands in diameter to become the sensory process, a membrane-limited bundle of 350–1000 parallel microtubules. The tip of the sensory process is firmly attached to a thin cap of exocuticle; mechanical depression of this cap, which probably occurs during walking movements, effectively stimulates the sensillum. The hypothesis is presented that the microtubules of the sensory process play an important role in mechanoelectric transduction in cockroach campaniform sensilla.     

Specialization of the hindgut wall for the attachment of symbiotic micro-organisms in a termite Procubitermes aburiensis (Isoptera,Termitidae, Termitinae)

The posterior colon of worker-caste termites accommdates an abundant, heterogeneous population of procaryotic organisms which are retained by attachment to prominent cuticular spines elaborated from the gut wall. The spines extend to nearly one half the diameter of the lumen and are each supported by a specialized root cell in which bundles of parallel microtubules traverse the cytoplasm from the apical to the basal surfaces. Additional epithelial cells are present which show infoldings of the apical plasma membrane and are overlain by cuticle containing deep, vase-shaped pits opening to the gut lumen. It is proposed that the root cells are designed to resist shearing forces transmitted to the base of each spine during contractions of the gut. The cuticular pits may represent sites of permeability to the end products of microbial metabolism.     

Light and scanning electron microscopy of the ecdysis of Haemonchus contortus infective larvae

During the second ecdysis of ruminant trichostrongyles, a region of the second molt cuticle is digested by a 44-kDa Zn-metalloprotease. We have examined this digestion process by light and scanning electron microscopy (SEM). The substrate region of the cuticle appeared, during the ecdysis process, as an indented ring at the 20th cuticular annulus coincident with the anterior terminus of the lateral alae. Continued digestion of the cuticle resulted in holes in the ring region that expanded until they became continuous and separation occurred between the anterior and posterior portions of the cuticle. Mechanical movements of the L3 forced aside the cuticle cap that generally remained attached on one side to the posterior portion as the larva escaped from the sheath. The site of secretion of the 44-kDa ecdysing enzyme causing cuticle digestion was not clear from morphological observations; however, existing evidence strongly points to the release of enzyme from the esophageal (pharyngeal) glands through the mouth.     

Fine structure of the secretory and sensory organs on the cephalon and the first pereionite of Trichoniscus alexandrae Caruso (Crustacea, Isopoda)

Trichoniscus alexandrae Caruso is a blind troglobiont isopod; males possess secretory and sensory organs on the cephalon and 1st pereionite consisting of cuticular pits hosting a tuft of setae and gland openings. Such organs are absent in females. Three types of cuticular structures have been observed: (a) lamellar setae, which likely play a role in protecting the gland openings and favouring the evaporation of secretions; (b) contact chemoreceptors, each provided with six bipolar sensory cells, a scolopale cell and enveloping cells; (c) a secretory cell complex, consisting of a long cylindrical slender duct-forming cell, with the function of transporting to the cuticular surface a secretion produced by two deeper secretory cells. The duct-forming cell is characterized by the presence of numerous microtubules in its cytoplasm, and is provided with a flattened duct. It is suggested that the secretion produced by the secretory cells could serve for sex-recognition.     

Ultrastructure de la Grégarine Callynthrochlamys phronimae Frenzel; Étude Comparée de son Noyau avec Celui de Thalicola salpae (Frenzel) (Eugregarina)

SYNOPSIS. The structure of the gregarine Callynthrochlamys phronimae has been studied with the electron microscope. The cuticular complex is not different from those previously described in other species of gregarines. It is composed of 2 layers of different thickness delimited by 3 unit membranes and constitutes series of oblique folds at the surface of the deutomerite. Longitudinal rods of dense material surrounded by a slight pellicle are seen under the cuticle. Pinocytic vacuoles are present under the surface of the gregarine. Cytoplasmic organelles include mitochondria, Golgi complexes, endoplasmic reticulum, vacuoles and dense bodies from different sizes. There is a connection between the different features of the cytoplasm in the protomerite and deutomerite and the corresponding cuticular organization.
A characteristic feature of the species is the peculiar differentiation of the nuclear membrane. The nucleus is surrounded by a typical double membrane of which the inner one has a dense fibrillar layer apposed to it. In mature trophozoites, tubular expansions without inner layer arise from the double membrane; the same type of nuclear membrane occurs in another species, Thalicola salpae.     

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.     

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.