Les relations isopedine - tissu osseux dans le post-temporal et les ecailJes de la ligne laterale de Latimeria chalumnae (Smith)

The scaly part of the posttemporal bone and the lateral-line scales have the same structure as other scales. However, the lateral line with its bony canal induces some local transformations in both structures. The posttemporal bone can be interpreted as a lateral-line scale whose "dermo"-component is extensively developed. With its composite structure, both osseous and scaly, the posttemporal bone affords an instance peculiarly well suited for studying the relationships between isopedine and bone. The observations demonstrate that isopedine whose superposed collagen layers make a double-twisted plywood, is a specialized structure which evolved from a bony tissue. The fibrous basal plate of a Latimeria scale is homologous to the osseous basal plate of a cosmoid scale.     

Ultrastructural data on the scales of the dipnoan Protoptems annectens (Sarcopterygii, Osteichthyes)

The structure and the mineralization of the scales of the living dipnoan (lungfish) Protoptems annectens have been investigated by transmission electron microscopy (TEM). The thin and imbricated scales are composed of two layers: the squamulae and the basal plate. At the outer surface, the squamulae form isolated plates superficially ornamented with spines and concretions and made up of acellular bone. After demineralization, the squamulae show a heterogeneous organic matrix composed of thin randomly oriented collagen fibrils forming a loose network within which the concretions appear as electronlucent circular areas. Abundant and aggregated concretions are located within the spines. The crystallites are oriented by the collagen fibrils except in the concretions. Anchoring bundles composed of parallel collagen fibrils arise from the squamulae and connect the scales to the overlying dermis.
The basal plate, the most developed part of the scale, is made up of isopedine. Its main component consists of thick, closely packed collagen fibrils organized in a 'double twisted plywood-like structure'. Fibroblasts are present in the basal plate. Mineralization occurs only in few plies located beneath the squamulae. Mandl's corpuscles are found in front of the mineralization front. The mineral deposit is oriented by the collagen fibrils.
The scales of Protoptems annectens differ from the typical elasmoid scales of the teleosts by the peculiar structure of the squamulae, nevertheless they show enough structural characteristics to support the hypothesis that they can be considered as scales of the elasmoid grade, which have retained some plesiomorphic characteristics.     

Scale structure in the Australian lungfish,Neoceratodus forsteri (Osteichthyes: Dipnoi)

Scales of the Australian lungfish, Neoceratodus forsteri, are secreted within the dermis by a capsule of scleroblasts, and enclosed in a pouch made of collagen fibers, in contact with the epidermis over the posterior third of the scale. Each scale grows from a focus, which represents the first formed part of the scale. On the internal surface of the scale is elasmodin, made of collagen fiber bundles arranged in layers. Elasmodin, unmineralized in N. forsteri, contains cells in the living animal, and the number of layers increases as the scales grow. Squamulin, on the thin external part of the scale, is also laid down in layers, and based on a matrix of fine collagen fibrils, mineralized with a poorly crystalline biogenic calcium hydroxylapatite. Squamulin is divided into separate sections called squamulae, and contains long tubules with cells applied to the wall of the tubule. The anterior and lateral surfaces of the squamulin are ornamented with pediculae, and the posterior surface has longitudinal ridges, from which collagen fibers extend to anchor the scale within the pouch. Elasmodin and squamulin are linked by unmineralized collagen fibrils. The layers, formed at irregular intervals, are connected around the margin of the scale, effectively converting the whole scale into a flat structure resembling a pearl, with the first formed tissues deeply embedded inside the scale, and the youngest on the outer surface. Incremental lines in the hard tissue, and the number of layers in the elasmodin, do not reflect the chronological age of the fish. J. Morphol. 276:1137–1145, 2015. © 2015 Wiley Periodicals, Inc.     

Evidence of denticles and attachment fibres in the superficial layer of scales in two fishes: Carassius auratus and Cyprinus carpio (Cyprinidae, Teleostei)

An attempt is made to clarify the mechanisms of the scale anchorage in two Cyprinidae, the goldfish and the carp. Scanning and transmission electron microscope investigations
revealed the presence of two different structures, denticles and collagen fibre bundles involved in the anchoring processes. These strucures are located on the upper part of the
scales. Denticles form minute processes on the circuli of the anterior areas of the scales. Collagen fibre bundles arise from the superficial layer connecting the scale to the overlying dermis. These fibre bundles show structural similarities with the Sharpey's fibres and are named Sharpey-fibre-like bundles. Such fibres of attachment, not previously reported, can be considered as usual anchoring structures in fish scales.     

Histology of Polypterus senegalus fin rays revisited

The present comparative histological study of the pectoral, caudal and anal fins of the polypterid Polypterus senegalus reveals the presence of a layer of dentine identified between the superficial ganoine patches and the bony part of the lepidotrichia in the three fins. Its extent varies depending on the fins. Similarly, the ganoine layer present at the surface of the proximal lepidotrichia shows fin-dependent differences in extent and distribution. The dentine layer is crossed by a system of thin worm-like vascular canaliculi that reach the ganoine layer and even penetrate within it as in the scales. In the lepidotrichia, the dentine lays directly on bone, which differs from the scales where dentine lies on isopedine, a plywood-like structure. Another difference between scales and lepidotrichia is the presence of actinotrichia that are unmineralised, fusiform rods of elastoidine located at the tip of the fins. Ontogenesis with differentiation of actinotrichia has no equivalent in scale formation. Although structural features are shared by lepidotrichia and scales in P. senegalus, observations on the scales and lepidotrichia support the hypothesis of Schaeffer (1977) that “scales and lepidotrichia are somewhat differently shaped manifestations of the same morphogenetic system”.     

Studies on fish scale formation and resorption. I. Fine structure and calcification of the scales in Fundulus heteroclitus (Atheriniformes: Cyprinodontidae)

Fine structure of the scales of Fundulus heteroclitus was examined by scanning and transmission electron microscopy. The concentric ridges of the scale surface were characterized by the presence of minute, highly calcified, denticles or tooth-like processes. Needle-shaped crystals of hydrox-yapatite were precipitated not only in the osseous layer but in the intimate lamellae of the fibrillary plate except in portions just below the grooves. The calcification of the osseous layer was observed to proceed by filling the matrix with patches of crystals. The fibrillary plate appeared to calcify by invasion of crystals from the upper calcified zone into spaces between collagen fibers.     

A study of the egg shells of the Falconiformes

A study of a selection of egg shells of the Falconiformes has been made similar to the earlier ones on ratites, the Anatidae and the Sphenisciformes. Chemical analyses, and histological and plastic embedding techniques were used.
The main part of the shell in all species studied consists of large crystals running through the shell. There was no layer of fine vertical crystals above this and no cover, and even the cuticle was not very pronounced. Histological studies showed no major differences, except that some shells had vacuoles in the outer layers. All such shells also gave an unetched outer layer when plastic embedded radial sections were studied and thin sections showed spaces between and within crystals. These spaces in the outer layers of the shell were of taxonomic interest for they were not present in the Cathartidae, the Falconidae and Sagittarius serpentarius.
Pore channels appeared to be much sparser than in other orders so far studied and all pores were single. Pigment was present on the surface of some shells, but it was also found in different layers of the shell right down to the cone layer and, in one case, had leaked through on to the membrane.
There were significant relationships between total and soluble shell nitrogen which divided the Falconidae from most of the Accipitridae but left Pernis and Pandion in an intermediate position.     

FINE STRUCTURE OF THE LARVAL ANURAN EPIDERMIS,WITH SPECIAL REFERENCE TO THE FIGURES OF EBERTH

Small pieces of skin from 8 cm long Rana clamitans larvae were fixed in OsO₄, washed, dehydrated, and embedded in a methacrylate mixture. Ultrathin sections were cut on a Porter-Blum ultramicrotome and were examined in an RCA electron microscope, type EMU 2D. The sections showed that aggregates of fibrous material in the cells of the inner layer of epidermal cells are identical in disposition and size with the classical figures of Eberth. It is conclusively shown that these figures do not arise from an aggregation of mitochondrial filaments. The tendency of the fibrils to concentrate on attachment points, or thickenings of the basal plasma membrane, is noted. It is also observed that numerous mitochondria are located in the distal region of the cells of the outer layer of epidermis in association with the secretory vacuoles. Microvilli are seen occasionally on the free surface of the skin. Cisternae are found only in the cells of the outer epidermal layer, while vesicular endoplasmic reticulum is found in the cells of both epidermal layers.     

On the nature of the horny scales of the pangolin

The pangolin scale is a horny derivative of the epidermis. It is complex in structure and is divisible into three distinct regions. The dorsal plate forms approximately one-sixth of the scale thickness. It is composed of flattened solid keratinized cells without basophilic nuclear remnants. This region tends to fray easily. The dorsal plate contains bound phospholipids and sulphydryl groups but is weak in disulphide bonds.
The bulk of the scale is made up of the intermediate plate formed of less flattened cells without basophilic nuclei. This region is rich in disulphide bonds but contains no appreciable bound phospholipids or sulphydryl groups.
The ventral plate is only a few cells thick and is rich in bound phospholipids, which also occur in the underlying scale bed epidermis.
These three regions of the scale are formed from separate epidermal germinal areas which do not develop a granular layer. Keratohyalin granules are, however, formed in the epidermis between the scales.
It is suggested on the basis of histological structure and dishribution of chemical constituents that pangolin scales are probably homologous with primate nails.
Evidence against the views that they are homologous with reptilian scales or are derived from compressed hairs is presented.     

Structure of the dermal scales in gymnophiona (Amphibia)

Histology and cytology of dermal scales of the gymnophionans Ichthyophis kohtaoensis and Hypogeophis rostratus reveal their structure and the nature of their mineralization. Dermal scales are small flat disks set in pockets in the transverse ridges of the skin. Each pocket contains several scales of various sizes. A ring of “hypomineralization” of varying diameter may occur on scales of a particular dermal pocket but bears no relation to the diameter of these scales. Three different layers form the scales and are seen on sections perpendicular to the surface. The cells of the basal layer lie deepest. Each of the two or three more superficial fibrous layers is composed of bundles of fibres that are oriented in parallel. The orientation varies among layers. The striation of the fiber scales has a periodicity comparable to that of the surrounding dermal fibers. Squamulae form a discontinuous layer on the scale surface and are the only mineralized part of the scale. The minerals are deposited both on the collagen fibers passing from the fibrous layers into the squamulae, and in the interfibrillar spaces. Spherical concretions, either isolated or coalescent, reaching up to 1 μm, are found on the surface of the squamulae. The dermal scales of Gymnophiona present some analogies with those of evolved bony fishes. Their characteristics could make them an original model for the study of mineralization.     

Scale morphology of greater lizardfish Saurida tumbil (Bloch, 1795) (Pisces: Synodontidae)

A comparative study comprising scale morphology and squamation of Saurida tumbil was conducted to identify the most useful scale and squamation characters within the different body regions and length groups and to clarify their significance for future systematic studies. The presence of the caudal pores is documented for the first time in teleosts. In addition, the presence of crenae and spines formed by posterior orientation and projection of circuli is recorded for the first time in a member of the Synodontidae. Scales of S. tumbil show some characters that are either never seen or they are exceedingly rare in scales of other teleosts. These are: two types of scalar denticles, denticles in the inter-circular area, and twin or Siamese scales. Several other scale characters have shown a consistent variation in different body regions and in fishes from different length groups. These are: focus position; bilobate rostral field edge; presence of three radii; long, narrow and separated crenae; papillae-form, crowded scalar denticles with posterior directed spines; the number of scale rows between anterior end of the dorsal fin and the lateral line.     

A histochemical study of keratinization in the domestic fowl (Gallus gallus)

The microanatomy of the epidermis of the domestic fowl is described and related to the distribution of various histochemical constituents involved in keratinization.
The avian horny layer over the back is composed of a loose network of structurally solid horny cells. This is in contrast to most mammalian epidermal horny cells in which structural keratin is found only in the peripheral cytoplasm, and the interior of the keratinocyte contains soluble products of cytolysis with possibly some free keratin filaments dispersed in the fluid material.
The avian tarsal epidermal horny scales show similarities to both the scales of lizards and snakes and to mammalian tail scales which appear to be homologous structures.
It is suggested that a thin layer of cells containing no detectable disulphide bonds, found in the tarsal scale region of the young chick, is probably mechanically weak and may function as a fission plane for sloughing of the horny layer. A specialized epidermis and thickened horny layer is developed in the fowl on the plantar underside of the toes, but this is quite different in structure from the mammalian plantar epidermis.
The overlapping of zones rich in ribonucleic acid (RNA) and bound cysteine (SH) in the growing feather suggests that protein synthesis and the preparatory stages to keratin disulphide bonding normally occur concurrently in feather formation. This is in contrast to the growing hair which has a region rich in RNA followed immediately before it becomes keratinized by a discrete keratogenous zone weak in RNA but rich in bound cysteine.     

A probable homologue of the clavicle in the holostean fish Amia calva

The two pairs of appendages associated with the throat region in Amia are described.
The posterior serrated appcndage of Amia calva is considered a homologue of the clavicle. This theory is based on topographical similarity (a bony element situated in front of the ventral part of the cleithrum and overlapping the anterior margin of the adjoining part of the cleithrum), structural similarity (cellular bone with ridges bearing denticles arranged in distinct patterns), ontogenetic similarity (early ontogenctic ossification with other dements of the dermal shoulder girdle prior to the appearance of scales), and phylogenetic cvidcnce (presence of similar elements in the caturid Furo ).
Although the anterior serrated appendage of A. calva exhibits structural and topographical similarities to both scales and clavicles, the ontogenetic evidence favours an homology with scales.
The ossicles located dorsolateral and lateral to the anteroventral part of the cleithrum in Lepisosteus oculatus share structural and topographical similarities to both scales and clavicles. However, ontogenetic evidence indicates that these ossicles are scales rather than fragmented clavicles.     

Structure and topographic distribution of oral denticles in elasmobranch fishes

The placoid scales, or denticles, of the external epidermis of elasmobranchs are well known as a hard protective coat over the skin to reduce abrasion or as elements to reduce hydrodynamic drag. However, the structure and function of denticles within the oral cavity is uncertain. Using stereological and scanning electron microscopy, this study examines the structure and distribution of oral denticles in a range of elasmobranchs. Of the batoids analyzed, only members of the Rhinobatidae possessed oral denticles, with no denticles found in the members sampled in the Gymnuridae or Dasyatidae. In contrast, oral denticles were located in all the selachians examined, except for members of the Orectolobidae. Within the selachians, the denticles of the Carcharhinidae have a grooved surface and a central spine, which is angled toward the posterior of the mouth. These denticular adaptations are beneficial to reduce hydrodynamic drag, an advantage for these free-swimming species with ram ventilation. Alternatively, members of the Hemiscyllidae have broad bulbous denticles that often overlap, providing a hard surface to protect the epithelium from abrasion during the consumption of hard-bodied prey. The distribution and high number of oral denticles appears to spatially compromise the capacity for oral (taste) papillae to populate the oropharyngeal cavity but provides increased friction and grip on prey items as they are manipulated within the mouth.     

Further studies on Nephroselmis and its allies (Prasinophyceae). II. Mamiella gen. nov., Mamiellaceae fam. nov., Mamiellales ord. nov.

The marine prasinophycean flagellate presently known as Nephroselmis gilva has been examined, using both the type culture and material from temperate (Denmark, New Zealand) and tropical waters (Thailand). All cell surfaces are covered with unmineralized scales, two types on the body, two on the flagella including flagellar hairs. The detailed structure of the scales is described, using high power electron microscopy of detached positive–stained scales. Previously overlooked organelles within the cell include large numbers of extrusive bodies, a rare type of organelle in chlorophyll–a– and –b–containing organisms, and an eyespot. N. gilva differs profoundly from the type species of Nephroselmis , and is transferred to the new genus Mamiella. Mamiella gilva is closely related to Mantoniella squamata. Together with the genus Dolichomastix they form the new family, Mamiellaceae, a small group of marine flagellates of worldwide distribution.
The members of the new family probably represent the most primitive extant prasinophytes. When compared with other members of the class, its species stand out, particularly by the lack of small square or diamond–shaped scales on the flagella and cell body. It is suggested that the Mamiellaceae should be referred to a separate order, Mamiellales.     

Epidermal fine structure of the toe tips of Sphaerodactylus cinereus (Reptilia, Gekkonidae)

This paper deals with epidermal structures of the sphaerodactyline gecko Sphaerodactylus cinereus : adhesive pads, cutaneous sensilla and intraepidermal axon terminals.
The adhesive pad is restricted to a single terminal scale and bears approximately 6,000 setae. The setae are complex, hair-like structures which branch and sub-branch up to five times. The terminal ends are shaped like inverted cones. They provide the friction which enables the gecko to walk even on vertical glass-plates.
Cutaneous sensilla of supposed mechanoreceptive function are found in groups of three or four at the anterior free edge of all dorsal and distal scales of the digit. The sensillum consists of a circular platelet in an epidermal depression bordered by an annular furrow and two or three bristles in a central position.
Discoid axon terminals in the digital scales are located between relatively stiff structures: the corneous layers of the epidermis and a layer of tonofibrillar bundles. The axon terminals are hypothesized to be sensitive to the internal pressure depending on hyperextension of the toe.     

QUANTITATIVE HISTOCHEMISTRY OF ACETYL-CHOLINESTERASE IN RAT HIPPOGAMPAL REGION CORRELATED TO HISTOCHEMICAL STAINING

Abstract— The quantitative histochemistry of acetylcholinesterase (AChE) has been examined in hippocampus (regio superior) and area dentata. Samples (0–05–2 μg) were dissected from freeze-dried tissue sections and assayed by either a colorimetric or a radiometric micromethod. In hippocampus the highest AChE activity occurred in a narrow zone just beneath the layer of pyramidal cells. Stratum oriens had a higher activity than stratum radiatum. A small peak of activity occurred in the lacunosal layer. In area dentata the overall activity was about 60 per cent higher than in the hippocampus. The highest activities were found in two zones adjacent to the granular layer.
When the results were expressed as activities per volume of tissue they correlated well with microdensitometric measurements on sections stained for AChE by the Koelle method.
Following transection of the fimbria the activity decreased to a low level, approaching a common value in the layers examined.
The results are discussed in relation to the significance of AChE in the hippocampal region.     

Scale morphology in Malawian cichlids

The morphology of 24 endemic cichlid species from Lake Malawi was studied with scanning electron microscopy. Several structures possibly of value for taxonomic and evolutionary studies were discovered. Six types of scale shapes and three types of interradial denticles were detected. The spiny area in the exposed part of the scale varied from nonexistent to 148° wide. Several regenerated scales with large focus and short radii were found. Various scale characters, which may prove valuable for phylogenetic purposes, are described and their use in phylogeny construction tested.     

Ontogenic development of surface ornamentation in the scales o fHemichromis bimaculatus (Cichlidae)

The scale surface of laboratory-raised Hemichromis bimaculatus selected from five age classes contains two regions, each characterized by a distinct ornamentation. The boundary between them corresponds to the anterior limit of the epidermis that covers the free region of the scale. In the overlapped region, the circuit and denticles are oriented toward the focus of the scale and form a classical pattern of ornamentation. During growth, the size of circuli and denticles does not change after they are formed. They appear stable at the species level and could thus be used in systematics. The ornamentation of the free region of the scale is composed of rounded tubercles, elongated ridges and sometimes ctenii. These structures appear long after the scales have been formed and thereafter grow and thicken throughout the life of the fish. The ontogenetic changes suggest that these characters should be used cautiously for taxonomic studies. The ridges of the scales of wild specimens are distinctly organized in a pattern that is lacking in laboratory specimens. Mechanical and hydrodynamical implications of the ornamentation are discussed.     

Freezing of tissue-limits for the autoradiographic localization of diffusible substances

Frozen thin sections and sections from freeze-dried and embedded tissue are used for the autoradiographic localization of diffusible substances at the electron microscope level. The presence of ice crystals in such sections may limit the autoradiographic resolution. Ice crystals are formed during freezing and may grow during subsequent processing of tissue. The contribution of ice crystal growth to the final image was estimated by measuring the distribution of the ice crystal sizes in freeze-etch replicas and in sections from freeze-dried and embedded tissues. A surface layer (10-15 mu) without visible ice crystals was present in both preparations. Beneath this surface layer the diameter of ice crystals increased towards the interior with the same relationship between crystal size and distance from the surface in the freeze-etch preparation as in the freeze-dry preparation. Ice crystal growth occurring during a much longer time during freeze-drying compared to freeze-etching does not significantly contribute to the final image in the electron microscope. The formation of ice crystals during freezing determines to a large extent the image (and therefore the autoradiographic resolution) of freeze-dry preparations and this probably holds also for thin cryosections of which examples are given.