Exoskeletal structure in the Ordovician trilobite Flexicalymene

Scanning Electron Microscope study of the exoskeletal ultrastructure of secondarily phosphatized material of Flexicalymene sp. from the Upper Ordovician Maquoketa Shale, Iowa, USA, shows that the exocuticle, comprising 20% of the total exoskeletal thickness, is composed of horizontal laminar units between 0.2 and 1 μm thick. These units consist of primarily mineralized organic fibres which form horizontal laminae interconnected by inter-laminae. The endocuticle is considerably more mineralized than the exocuticle, and its original organic structure cannot be observed in untreated preparations. Etching with chromium sulphate reveals: (1) horizontal organic laminar units, 0.2 to 2 μm thick, and (2) pore canals with non-twisted walls about 0.3 μm in diameter. Exuvia cannot be distinguished from the exoskeletons of dead animals. The exoskeletal ultrastructure in trilobites agrees essentially with that in crustaceans.     

Ultrastructural shape and three-dimensional organization of the intracuticular canal systems in the mineralized cuticle of the green crab Carcinus maenas

Two main self-contained canal systems are present in the crab mineralized cuticle. The first, or fibre canal system, is constituted by simple, unbranched vertical canals containing axially running fibres in close association with myoepidermal junctions. The second, or pore canal system, is composed of procuticular pore canals and epicuticular channels that prolong the procuticular canals. In opposition to widespread opinion, pore canals make up a three-dimensional branched system extending from the apical plasma membrane of the epidermis up to the epicuticle. Branching occurs by projections of lateral horizontal from the vertical canals at the lower level of the pigmented layer and by innumerable ramifications of epicuticular canals. In agreement with Neville's model for insects, vertical procuticular pore canals of crustacean mineralized cuticle, and also fibre canals, exhibit a twisted ribbon structure reflecting the helicoidal arrangement of the horizontal chitin-protein microfibrils.     

La formation des canaux cuticulaires chez l'adulte de Tenebrio molitor L. étude ultrastructurale et remarques histochimiques

The sclerotized cuticle of adult Tenebrio shows (1) an exocuticle composed of rotating lamellate layers and of columns of cuticular material, the fibres of which run perpendicularly through the lamellae, (2) an endocuticle composed of layers with preferred orientation. In the exocuticle, the pore canals are numerous and run along the columns; they do not rotate with the lamellate layers. They show several filaments some of which leave the canals and form a dense intracuticular network. In the last layers of exocuticle, the pericolumnar canals fuse and form large endocuticular canals which rotate in phase with the cuticular fibres. The formation of columns and canals is in relation with cellular expansions which penetrate into the cuticle during cuticle deposition. Exocuticular columns seem characteristic of highly sclerotized cuticles and the intracuticular filaments may have a role in the transport of sclerotisation precursors.     

The membranous labyrinth and its innervation inChaetodon trifasciatus (Pisces,Teleostei, Chaetodontidae)

Synopsis In the butterflyfishChaetodon trifasciatus, the labyrinth is characterized by its elevated form and especially the size of the vertical canals, the almost circular form of the horizontal canal and its posterior opening not directly in the utriculus but in the common pillar of the two vertical canals. There is an almost complete separation between utriculus and sacculus which are only linked by a virtual pore. The lagena, which is medially situated to the posterior part of the sacculus, is separated from it by an incomplete vertical wall. There are two maculae neglectae, the anterior macula being situated in the pore separating utriculus from sacculus and filling this pore, the posterior in a gutter of the floor of the utriculus. A long and narrow endolymphatic canal, originating from the sacculus close to the communication with the utriculus, follows the common pillar of the two vertical canals and widens into an endolymphatic sac at the top of the membranous labyrinth. The innervation of the labyrinth is made by the acoustic ganglion, which is connected to the brain by two roots and elongated into three parts: the anterior part innervates the anterior and horizontal cristae and the utricular and saccular maculae; the middle part innervates the macula sacculae and the macula neglecta 1; the posterior part innervates the macula neglecta II, the macula lagenae and the posterior crista. The important size of the vertical canals and the almost circular form of the horizontal canal may reflect very precise locomotory aptitudes.     

Interrelations between auditory and vestibular receptors in the frog's labyrinth

Summary The influence of the efferent vestibular system being eliminated, the spontaneous activity of afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By functionally eliminating either both papillae or all the vestibular receptors except for the papillae, and then using statistical methods, as well as by stimulating the papillae by sounds or the papillary nerve fibres by electrical stimulus, it has been shown that the auditory papillae have a facilitatory influence on the spontaneous afferent activity from the horizontal and vertical anterior canals. This influence is most likely mediated by receptor-receptor fibres arising from the auditory organs and innervating the semicircular canals.Abbreviations HC horizontal canal - VAC vertical anterior canal This research was supported by a grant from D.G.R.S.T. (Aide à la Recherche n 77.7.1127)     

PORE CANALS AND RELATED STRUCTURES IN INSECT CUTICLE

The fine structure and the distribution of an esterase have been studied in the cuticle of Galleria larvae, Tenebrio larvae and pupae, and in the wax-secreting cuticle of the honey bee, and compared with those in the cuticle of the caterpillar of Calpodes. In Galleria and Tenebrio the pore canals are spaces passing through the lamellate endocuticle from the epithelium to the epicuticle. They contain a filament from the cells which may be concerned in their formation. The shape of the pore canal is probably determined by the orientation of the fibres making up the lamellae in the endocuticle and is not a regular helix. The pore canals also contain numerous filaments of another sort which pass on through the epicuticle and are believed to be the origin of the surface wax. They are particularly abundant in the pore canals of the honey bee wax-secreting cuticle and extend into the cell in long pockets surrounded by an envelope of the plasma membrane. The esterase is probably concerned with the final stage of wax synthesis, for its distribution is similar to that of the lipid filaments.     

八种鸡形目鸟类卵壳及壳膜超微结构观察

８种鸡中,高原山鹑卵壳仅由乳突层和栅栏层构成,缺少护膜层,表面无裂纹,外气孔开放。其它种类由乳突层、栅栏层和护膜层构成,表面有裂纹、外气孔有覆盖。栅栏层都有与飞翔相适应的气泡,飞翔能力强,速度快的种类产卵壳气泡密度高的卵。     

Molecular architecture of adult locust cuticle at the electron microscope level

It is shown that locust adult endocuticle consists of a daily alternation of two types of chitin-protein architecture: (i) non-lamellate day layers with microfibrils oriented in a preferred direction, traversed by pore canals whose shape resembles an untwisted ribbon, (ii) lamellate night layers with helicoidally oriented microfibrils traversed by pore canals shaped like regularly twisted ribbons. Uncoupling the circadian clock which normally controls the timing of these two types leads to growth of cuticles which are organized like one or the other throughout. We can thus experimentally change the architecture of the microfibrils which in turn changes the pore canals.     

Electrosensitive spatial vectors in elasmobranch fishes: implications for source localization

The electrosense of sharks and rays is used to detect weak dipole-like bioelectric fields of prey, mates and predators, and several models propose a use for the detection of streaming ocean currents and swimming-induced fields for geomagnetic orientation. We assessed pore distributions, canal vectors, complementarity and possible evolutionary divergent functions for ampullary clusters in two sharks, the scalloped hammerhead (Sphyrna lewini) and the sandbar shark (Carcharhinus plumbeus), and the brown stingray (Dasyatis lata). Canal projections were determined from measured coordinates of each electrosensory pore and corresponding ampulla relative to the body axis. These species share three ampullary groups: the buccal (BUC), mandibular (MAN) and superficial ophthalmic (SO), which is subdivided into anterior (SOa) and posterior (SOp) in sharks. The stingray also has a hyoid (HYO) cluster. The SOp in both sharks contains the longest (most sensitive) canals with main projections in the posterior-lateral quadrants of the horizontal plane. In contrast, stingray SO canals are few and short with the posterior-lateral projections subsumed by the HYO. There was strong projection coincidence by BUC and SOp canals in the posterior lateral quadrant of the hammerhead shark, and laterally among the stingray BUC and HYO. The shark SOa and stingray SO and BUC contain short canals located anterior to the mouth for detection of prey at close distance. The MAN canals of all species project in anterior or posterior directions behind the mouth and likely coordinate prey capture. Vertical elevation was greatest in the BUC of the sandbar shark, restricted by the hammerhead cephalofoil and extremely limited in the dorsoventrally flattened stingray. These results are consistent with the functional subunit hypothesis that predicts specialized ampullary functions for processing of weak dipole and geomagnetic induced fields, and provides an anatomical basis for future experiments on central processing of different forms of relevant electric stimuli.     

The ultrastructure of the cuticle of adult female Mermis nigrescens (Nematoda)

The ultrastructure of the cuticle of the adult female nematode Mermis nigrescens has been described. There is an epicuticle and three-layered membrane covering the cuticle. The cortex is penetrated by canals which extend from the surface of the cuticle to the matrix of the layer beneath the cortex. Beneath the cortex are two layers of giant fibres which spiral around the nematode, a thick layer containing a network of fibres and a basal layer containing a vacuolated matrix material. it is thought that the epicuticle is secreted from the canals in the cortex. The possible functions of the layers in the cuticle have been discussed and similarities with the cuticle of the Acanthocephala have been noted.     

The comparative ultrastructure of the egg membrane and associated pore structures in the starry flounder,Platichthys stellatus (Pallas), and pink salmon,Oncorhynchus gorbuscha (Walbaum)

Eggs of the starry flounder (Platichthys stellatus) and pink salmon (Oncorhynchus gorbuscha) were examined by scanning and transmission electron microscopy to determine differences in egg membrane structure with reference to contrasting ecological conditions in which the eggs normally develop. The egg membrane of the starry flounder constitutes 0.22--0.50% of the egg's diameter. The zona radiata is composed of 6 continuous horizontal lamellae, covered by a thin triple layered border, and pierced by numerous regularly spaced pore canals. The micropyle canal measures 8 microns at the opening and tapers to 3.6 microns as it penetrates the membrane. In contrast, the thicker membrane of the pink salmon egg forms 0.80--1.0% of the egg's diameter, is composed of numerous short discontinuous lamellae which are pierced by pore canals, and is covered by a coating of irregular thickness. The 15--16 micron micropyle opening is surrounded by an area of protrusions, and the funnel-shaped canal tapers to 2 microns at its terminal aperture. Contrasting environmental conditions during embryogenesis of these two species may be reflected by the thin membrane and simple lamellar structure in the pelagic egg of the starry flounder, and the thick membrane and complex lamellar structure in the demersal egg of the pink salmon.     

Comparison of the lateral line and ampullary systems of two species of shovelnose ray

The anatomical characteristics of the mechanoreceptive lateral line system and electrosensory ampullae of Lorenzini of Rhinobatos typus and Aptychotrema rostrata are compared. The spatial distribution of somatic pores of both sensory systems is quite similar, as lateral line canals are bordered by electrosensory pore fields. Lateral line canals form a sub-epidermal, bilaterally symmetrical net on the dorsal and ventral surfaces; canals contain a nearly continuous row of sensory neuromasts along their length and are either non-pored or pored. Pored canals are connected to the surface through a single terminal pore or additionally possess numerous tubules along their length. On the dorsal surface of R. typus, all canals of the lateral line occur in the same locations as those of A. rostrata. Tubules branching off the lateral line canals of R. typus are ramified, which contrasts with the straight tubules of A. rostrata. The ventral prenasal lateral line canals of R. typus are pored and possess branched tubules in contrast to the non-pored straight canals in A. rostrata. Pores of the ampullae of Lorenzini are restricted to the cephalic region of the disk, extending only slightly onto the pectoral fins in both species. Ampullary canals penetrate subdermally and are detached from the dermis. Ampullae occur clustered together, and can be surrounded by capsules of connective tissue. We divided the somatic pores of the ampullae of Lorenzini of R. typus into 12 pore fields (10 in A. rostrata), corresponding to innervation and cluster formation. The total number of ampullary pores found on the ventral skin surface of R. typus is approximately six times higher (four times higher in A. rostrata) than dorsally. Pores are concentrated around the mouth, in the abdominal area between the gills and along the rostral cartilage. The ampullae of both species of shovelnose ray are multi-alveolate macroampullae, sensu Andres and von Düring (1988). Both the pore patterns and the distribution of the ampullary clusters in R. typus differ from A. rostrata, although a basic pore distribution pattern is conserved.     

Pore canal shape related to molecular architecture of arthropod cuticle

The rotating structure of pore canals is interpreted in terms of the Bouligand model of rotating layers of chitin-protein microfibrils, and the daily growth layer system in insects. Crustacean and arachnid examples are also used. Pore canals are flattened into ribbons by neighbouring microfibrils. The ribbons run straight when traversing layers with preferred microfibril orientation, but rotate in phase through lamellate layers in which the layers of microfibrils also rotate. Oblique sections of models show that the parabolic artefact derived from microfibrils, and the parabolic arcs of pore canals seen as crescents in section, only superimpose, as they do in actual sections, when both systems have the same sense of rotation. Pore canal rotation may be determined by chitin-protein architecture.     

Structure of the sex pheromone-producing prothoracic glands of the male old house borer,Hylotrupes bajulus (L.) (Coleoptera : Cerambycidae)

Pheromone glands were discovered in the prothorax of male Hylotrupes bajulus (L.) (Coleoptera : Cerambycidae). These exocrine glands were investigated by SEM and light microscopy. Almost the entire prothorax is internally lined with a glandular matrix composed of numerous heap-like complex glands. Each gland is divided into several subunits (“pore field units”), which in turn are composed of a varying number of glandular units. The glandular unit comprises a distal voluminous glandular cell, a medial (intercalary) canal cell I, and a minute canal cell II near the cuticle. The spindle-like, basally constricted receiving canal of the gland cell leads into the long, non-porous conducting canal, which, by a single cuticle canal, opens in an external pore field, an aggregate of orifices of other such cuticle canals. In varying numbers, these randomly arranged pore fields are located in superficial pits that are distributed over nearly the entire prothorax. The structure of these male sex pheromone glands is discussed in comparison with other known glands in species of Coleoptera characterized by multicellular aggregations and by pore plates.     

Electron microscopic and preparative methods for the analysis of isopod cuticle

The crustacean cuticle consists of a complex organic matrix and a mineral phase. The physical and chemical properties of the cuticle are corellated to the specific functions of cuticular elements, leading to a large variety in its structure and composition. Investigation of the structure-function relationship in crustacean cuticle requires sophisticated methodological tools for the analysis of different aspects of the cuticular architecture. In the present paper we report improved preparation methods that, in combination with various electron microscopic techniques, have led to new insights of cuticle structure and composition in the tergite cuticle of Porcellio scaber. We used thin sections of non-decalcified tergites and decalcified resin embedded material for transmission electron microscopy and scanning transmission electron microscopy. Etched sagittal planes of bulk tergite samples were analysed with field emission scanning electron microscopy. We have found a distinct distal region within the exocuticle that differs from the subjacent proximal exocuticle in the arrangement of fibres. Within this distal exocuticle chitin-protein fibrils assemble to fibres with diameters between 15 and 50 nm that are embedded in a mineral matrix. In the proximal exocuticle and the endocuticle fibrils do not assemble to fibres and are surrounded by mineral individually. Furthermore, we show that the pore canals are filled with mineral, and demonstrate that mild etching of polished sagittal cuticle surfaces reveals regions containing mineral of diverse solubility.     

Modelling mechanically stable muscle architectures.

This paper presents a planar architectural model for an activated skeletal muscle, with mechanical equilibrium throughout the muscle belly. The model can predict the shape of the muscle fibres and tendinous sheets as well as the internal pressure distribution in the central longitudinal plane (perpendicular to the tendinous sheets) of uni- and bipennate muscle bellies. Mechanically stable solutions for muscle architectures were calculated by equating the pressure developed by curved muscle fibres with the pressure under a curved tendinous sheet. The pressure distribution under a tendinous sheet is determined by its tension, its curvature and the tensile stress of the attached muscle fibres. Dissections showed a good resemblance of the architecture of embalmed muscles with those from our simulations. Calculated maximum pressures are in the same order of magnitude as pressure measurements from the literature. Our model predicts that intramuscular blood flow can be blocked during sustained contraction, as several experimental studies have indeed demonstrated. The volume fractions of muscle fibres and interfibre space in the muscle belly were also calculated. The planar models predict a too low volume fraction for the muscle fibres (about 45% for the bipennate models with a straight central aponeurosis, and about 60% for the simulated unipennate muscle). It is discussed how, in a real muscle, this volume problem can be solved by a special three-dimensional arrangement of muscle fibres in combination with varying widths of the tendinous sheets.     

Spatial coordination of compensatory eye movements in vertebrates: form and function

The semicircular canals of the labyrinth of vertebrates provide one way of motion detection in three-dimensional space. The fully developed form of the vertebrate labyrinth consists of six semicircular canals, three on each side of the head, whose spatial arrangement (vertical canals are placed diagonally in the head, horizontal canals are oriented earth horizontally) follows three interconnected principles: 1) bilateral symmetry, 2) push-pull operational mode, and 3) mutual orthogonality. Other sensory and motor systems related to vestibular reflexes, such as the extraocular muscles or the "optokinetic" coordinate axes encoded in the activity of the visually driven cells of the accessory optic system, share the same geometrical framework. This framework is also reflected in the anatomical networks mediating compensatory eye movements, linking each of the semicircular canals to a particular set of extraocular muscles (so-called principal vestibuloocular reflex connections to yoke muscles). These classical vestibulo-oculomotor relationships have been verified at many levels of the vertebrate hierarchy, including lateral- and frontal-eyed animals. The particular spatial orientation of the semicircular canals requires further comment and phylogenetic evaluation. The spatial arrangement of the vertical canals is already present in fossil ostracoderms, and is also exemplified in lampreys, the modern forms of once abundant agnathan species that populated the Silurian and Devonian oceans. The lampreys and ostracoderms lack horizontal canals, which appear later in all descendent vertebrates. The fully developed vertebrate labyrinth with its six semicircular canals displays distinct differences that are obvious when comparing distant taxa (e.g. elasmobranchs versus other vertebrates). Whereas the common crus of the semicircular canals in teleosts through mammals is formed between the anterior and the posterior semicircular canal, it occurs between the anterior and the horizontal canal in elasmobranchs. However, despite this morphological difference, these two vertebrate labyrinth prototypes constitute a functionally identical solution. A similar analysis holds for certain invertebrate species (crab, octopus, squid), which display an even wider variety in the physical expressions of movement detection systems when compared to vertebrates. Although the physical expressions of motion detection systems differ in the animal kingdom, the functional solutions (providing the best signal-to-noise ratio) with adherence to bilateral symmetry, push-pull operational mode, and mutual orthogonality are identical.(ABSTRACT TRUNCATED AT 400 WORDS)     

The fine structure of the outer surface of the incubated eggshells of the Helmeted guinea fowl (Numidia meleagris)

The surface of the eggshells of the Helmeted guinea fowl (Numidia meleagris) was polished during incubation by the parent. Examination with the light microscope showed that the cuticle had been removed from the ridges on the outer surface of the shell and that the plugs in the outer orifice of the pore canals had acquired extraneous materials including grease. Studies with a scanning electron microscope revealed that the spheres that made up the pore plugs retained their identity even though they were stained. It was concluded that ridges on the shell surface protected the pore plugs from damage by attrition and that the plugs acted as filters thereby preventing nest debris from occluding the pore canals or contaminating the shell membranes.