Heinz Splechtna

Fine structure of the dorsal lingual epithelium of Trachemys scripta elegans (Chelonia: Emydidae)

Turtles are adapted to different environments, such as freshwater, marine, and terrestrial habitats. Examination of histological and ultrastructural features of the dorsal lingual epithelium of the red‐eared turtle, Trachemys scripta elegans, and comparison of the results with those of other turtles should elucidate the relationship between the morphology of tongues as well as the fine structure of lingual epithelia and chelonian feeding mechanisms.

DORSAL LINGUAL EPITHELIUM OF PLATEMYS PALLIDIPECTORIS (PLEURODIRA, CHELIDAE)

Scanning electron microscopy reveals that the flat tongue of Platemys pallidipectoris has shallow grooves and no lingual papillae. The surface of the tongue is covered with dome‐shaped bulges, each corresponding to a single cell. Short microvilli are distributed over the cell surface. Light microscopy shows a stratified cuboidal epithelium with an underlying strong connective tissue. Transmission electron microscopy indicates four layers. The basal cells of the epithelium are electron‐translucent and have a large central nucleus and a cytoplasm with keratin tonofilaments. Plasma cells with abundant rough endoplasmic reticulum and mitochondria occur in the basal layer. Production of secretory granules begins in the more electron‐dense intermediate layers and increases as the cells move toward the surface. The membranes of the cells of the deep intermediate layer form processes that project into relatively wide intercellular spaces. In the superficial intermediate layer, the cytoplasm of the cells contains numerous fine granules; these increase in number but not in size in more distal layers. The cells of the surface layer are electron‐translucent with a round nucleus. Contents of their fine granules are secreted into the oral cavity.

Struktur- und Funktionsanalyse ophiocephaler Pedizellarien vonSphaerechinus granularis Lam.,Echinus acutus Lam. undParacentrotus lividus Lam. (Echinodermata, Echinoidea)

SummaryThe ophiocephalous pedicellariae of three adratic species of sea urchins have been investigated by the aid of scanning electron microscope regarding the structure of the skeletal ossicles and by the aid of light microscope to elucidate the function of muscles und connective tissue structures. Each valve bears a double central and 2 simple peripheric articulations. Their interactions cause synchronous movements of the 3 valves as well as they enable the peripheral gripping teeth to meet exactly whilst the jaws are closing. Beside the basic handles, which pass over each other when the valves are moving, so-called Innenbügel are arranged at the base of the central articulation of 2 valves. They bear the insertions of the 2 collagen ligaments, which connect the neck with the head of the pedicellariae, without hampering movements of jaws. In the region of the handles, the connective tissue consists of 2 collagen ligaments, which run loop-like over the edges of the handles. Position and structure allow them to increase the gripping power and to lock the articulations for a longer period without the aid of the muscles. The movements of the flexible neck, necessary for the function of the whole pedicellariae are produced by interplaying of the Mm. flexores and the connective tissue stem, which is acting like a hydroskeleton.ZusammenfassungDie ophiocephalen Pedizellarien dreier adriatischer Seeigelarten wurden hinsichtlich ihres Skelettaufbaues mit dem Rasterelektronenmikroskop, zur funktionellen Analyse der Muskulatur und des Bandapparates lichtoptisch untersucht. Jede Skelettklappe verfügt über ein doppeltes zentrales Gelenk und 2 einfachere periphere Gelenke, die nach dem Prinzip einer doppelten Dreiecksführung sowohl die Synchronbewegung der 3 Klappen als auch das präzise Ineinandergreifen der nur wenige μm großen Randzähnchen ermöglichen. Neben den bekannten basalen Bügelbildungen, die bei der Bewegung ineinandergleiten, tragen 2 Klappen sog. Innenbügel, die dem zentralen Ansatz des Bandapparates dienen. Dieser verbindet das Köpfchen, ohne dessen freie Beweglichkeit zu behindern, mit dem beweglichen Halsabschnitt. Im Bereich der Bügel ist der Bandapparat in 2 Bänder aufgelöst, die schlaufenartig diese Bügel umgreifen. Zufolge ihrer Lage und ihrer Struktur können sie einerseits die Beißwirkung verstärken, andererseits die Gelenke längere Zeit sperren ohne Dauerbelastung der Muskulatur. Die für die Funktion erforderlichen Bewegungen des Halsabschnittes erfolgen im Zusammenspiel der Mm. flexores mit dem als Hydroskelett wirksamen achsialen Bindegewebeschlauch.

The tadpole of Bufo brongersmai Hoogmoed 1972

The tadpole of the north african toad Bufo brongersmai is described for the first time in chronological developmental stages from hatching to the onset of metamorphosis based on a complete ontogenetic series. The structure of the oral disk and of the buccopharyngeal cavity are shown. Fifteen metric parameters are described in eight tadpole size classes by means of standard statistical methods and they are compared with those of other circummediterranean Bufo species. The eidonomic characteristics of the tadpole of B. brongersmai turn out to be intermediate between B. bufo and B. viridis.

Zur Feinstruktur ophiocephaler Pedizellarien von Arbacia lixula (Linné) (Echinodermata, Echinoidea)

SummaryThe stalk of the pedicellariae from Arbacia lixula was investigated by the aid of light- and electron microscope and analysed regarding to its function. It consists of a bundle parallel arranged calcite rods concentrated distally in the head of the stalk, which is of trabecular construction; toward the corona they terminate freely without forming a joint surface. Inside, between the calcite rods and also as a distinct mantle around them, there are collagenous fibers of various thickness in parallel and spiral arrangement. In the lower part of the stalk the collagenous fibers pass over more and more to the peripheric mantle, which envelops the broader base of the stalk in constant thickness. Inside of the skeleton-collagen cylinder there appears now distinct accumulation of cells; their processes are to be find at the outer surface of the calcite fibers and their nuclei are arranged in a clear layer just above the joint region. In the area between the free ends of the calcite rods and the tubercle of the corona there is a cushion built up by fine fibrils. Its special function is given by the fact, that in any case of movement of the stalk, the calcite fibers are able to dip into this cushion more or less. Concerning the innervation, the separation of a series of nerves from the basal nerve ring, their free course in the stalk and their passing to the Mm. flexores of the head of pedicellaria is described. Based on all findings a functional interpretation for the special combination of skeleton and organic fibers is given.ZusammenfassungDer Stiel der Pedizellarien von Arbacia lixula wurde lichtund elektronenoptisch untersucht und hinsichtlich seiner Funktion analysiert. Er besteht aus einem Bündel parallel angeordneter Calcitfasern, die distal von dem trabekulär aufgebauten Stielköpfchen zusammengefaßt werden; proximal enden sie frei. Zwischen den Skelettfasern im Inneren und als deutliche Ummantelung derselben finden sich parallel, sowie auch schraubig angeordnete Kollagenfasern unterschiedlicher Dicke. In den Raum zwischen den freien Enden der Calcitfasern und dem Gelenkhöcker der Corona schiebt sich ein funktionell wesentlicher Polster feiner Fibrillen, in den die Skelettfasern bei der Bewegung verschieden tief eintauchen können. Hinsichtlich der Innervation wird die Abspaltung einer Reihe von Nerven aus dem basalen Ringnerv, ihr freier Verlauf im Stiel und ihr Übertritt in die Mm. flexores des Pedizellarienköpfchens dargestellt. Aufgrund der erhobenen Befunde wird eine funktionelle Deutung dieser für Echinodermen besonderen Kombination von Skelett und organischem Fasermaterial gegeben.

Renal vasculature and uriniferous tubules in the common iguana

The pattern of vascular supply and the histology of uriniferous tubules of the kidney in the common iguana were studied by light microscopy of semithin sections and by scanning electron microscopy of microcorrosion casts. The corrosion casts showed a strongly developed renal portal system that forms an extensive capillary network throughout the kidney. Glomeruli are numerous and have a capillary pattern consisting of three to six loose coils of capillaries intercalated between afferent and efferent arterioles. Glomeruli are ovoid in shape and relatively small (mean diameter of the casts: 67 ± 19 μm in short axis and 79 ± 18 μm in long axis). Each glomerulus has a single afferent arteriole and efferent arteriole. The length and volume of the glomerular capillaries per unit volume of renal corpuscle are 0.0029 ± 0.0008 μm/μm3 and 0.321 ± 0.077, respectively. A short neck segment consisting of low epithelial cells is interposed between Bowmans capsule and the proximal tubule. A close association between the distal tubule and the glomerular hilus can be interpreted as a juxtaglomerular apparatus.

The vascular structure of the kidney of the neotenous axolotl and its metamorphosed counterpart

The renal vascular and glomerular structures of the kidney of neotenous and experimentally metamorphosed axolotls (Ambystoma mexicanum: Amphibia, Urodela) are investigated using light, transmission electron, and scanning electron microscopy of critical‐point dried specimens and vascular corrosion casts. The blood vascular system of the kidney in the axolotl is generally similar to that in other urodeles. The glomeruli are comparatively large and distincly ovoid (mean size 267 × 201 μm). Glomerular endothelial nuclei frequently bulge into the vascular lumen. Whereas the lamina rara externa and the lamina densa are quite uniform in diameter, the lamina rara interna shows a very irregular thickness with frequent interposed cellular processes. In the thyroxine‐metamorphosed animals, the glomerular surface decreased by a factor of approximately 36%; this was mainly due to the reduction of the glomerular diameter in the direction from vascular to urinary pole. No significant degeneration or new formation of renal tubules was observed during or after metamorphosis. A notable relative decrease in renal volume (approx. 57%) in the metamorphosed forms can be attributed mainly to a reduction in interstitial volume.

Die Entwicklung ophiocephaler Pedizellarien vonSphaerechinus granularis (Echinodermata, Echinoidea)

SummaryThe development of the ophiocephalous pedicellariae ofSphaerechinus granularis was investigated by means of a continuous series of regenerating pedicellariae with the aid of a scanning electron and light microscope. The anlagen of the three valves appears in the form of isolated triradiate skeleton rudiments; the central axis arises from their center. At the deepest level, the basal plate develops from this horizontal structure, which at last forms the handle segment of the valve. Two more horizontal plates are built above this basal plate, which are supported by spool-shaped elements; around these skeletal elements the connecting collagenous fibers are arranged. Starting from the central axis, five parallel skeletal rods arise under regular ramification and arrangement; they are connected to one another by a meshwork forming the central stem (axis tube). In a similar way, the muscle baskets on both sides of the axis tube are built up, arising from the level of the first horizontal plate. As a median support of the axis tube against the horizontal plate, a vertical, perforated plate develops with the differentiation of the central articulations at its free margin. This middle segment of the valve, as well as the handle segment, proceeds in its development, while the distal, biting segment is more retarded in its increase. Both facts can be proved by function. The final differentiation of the margins of the distal valve segment with regard to the precise meeting of the gripping teeth takes place under the influence of the beginning movements of the valves. Therefore, full differentiated articulations and adequate muscle systems are necessary.Coincidently, reorganization takes place as long as the central articulations and the distal, biting valve segment are joined to a functional unit, with the muscle baskets for the Mm. adductores at both sides. In the same way, the handle segment, the superstructure of the insertions of the Mm. abductores at the outside of the valve, and the supporting structures of the distal segment of the valve all evolve into a functional unit. The primary, rather descriptive formation of a valve into a distal, middle, and handle-bearing segment gets partly lost from this point of view.This reconstruction also becomes clear by the decrease of the perforated plate structure for the benefit of a framework construction by apposition of compact material at stronger loaded zones; highly stressed structures as articulations receive a layer of polycrystalline calcite. A similar allometry, also based on functional conditions, can be seen in the three segments of the entire pedicellariae — head, neck, and stalk — because the neck, which is the essential part for the later high mobility of the head, does not start growing before the final organization of both other segments.ZusammenfassungDie Entwicklung ophiocephaler Pedizellarien beiSphaerechinus granularis wurde anhand einer kontinuierlichen Reihe von Regeneraten rasterelektronenoptisch und lichtmikroskopisch studiert. Nach Anlage der skelettogenen Grundelemente zeigt sich eine deutliche Wachstumsallometrie der 3 Klappenabschnitte, indem der Bügelabschnitt und besonders der mittlere Klappenteil in der Entwicklung gegenüber dem distalen beißenden Teil vorauseilen. Die Enddifferenzierung der Klappenränder mit der genauen Passung ihrer Zähnchen, das Einschleifen der Gelenke und die endgültige Ausgestaltung der Bügel erfolgen unter dem formenden Einfluß der beginnenden Bewegung. Die ursprüngliche deskriptive Gliederung in distalen, mittleren und bügeltragenden Abschnitt wird mehr und mehr durch funktionelle Einheiten ersetzt; gleichzeitig wird auch die anfängliche Lochplattenstruktur von einer Rahmenkonstruktion abgelöst. Eine gleichfalls funktionell begründbare Allometrie ergibt sich in der Entwicklung von Köpfchen, Hals und Stiel des gesamten Pedizellars.

Scanning electron microscopy of vascular corrosion casts of the glomeruli of two species of turtles

Scanning electron micrographs of microcorrosion casts of the renal vascular system of Pseudemys scripta and Testudo hermanni show fairly well‐developed, round glomeruli in the former (mean diameter of casts: 83.1 μm) and fewer but bigger, ovoid glomeruli (mean diameter of casts: 111.1 μm/131.6 μm) in the more arid‐adapted. T. hermanni. Furthermore, the intrarenal development of the pertiubular capillary system differs in these two species. These relatively minor morphological differences correlate well with the major differences in the ecology of these species, as well as with physiological data on urine composition from the literature.

Endothelial nuclear bulging: Morphological evidence for an intraglomerular perfusion regulating mechanism in the axolotl

Kidneys of the Axolotl (Ambystoma mexicanum: Urodela, Amphibia) have been investigated by light and electron microscopy as well as microvascular corrosion casting. Numerous glomerular endothelial nuclei bulge into the glomerular capillary lumen. It is concluded that these cells virtually stop the blood-flow in the respective vessel by blockage of erythrocyte passage. A proposal for an intraglomerular regulation mechanism of capillary perfusion (and thus filtration) by endothelial isometric contraction in the Axolotl is made on the basis of morphological methods.