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1.
A study of the tissues of the teeth and jaws in piranhas, using the scanning electron microscope and various techniques of light microscopy, revealed many dental adaptations related to the specialized feeding habits of these carnivorous fishes. The dentition is primarily sectorial, although some anterior teeth may be used in grasping. The scissor-like rows of teeth are maintained by the specialized pattern of tooth replacement. The bones of the jaws and the tooth attachment support the teeth very firmly. In its structural organization, the enameloid covering the teeth closely resembles that on the sectorial teeth of sharks and is adapted to the probable stress patterns set up in biting.  相似文献   

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By means of radioimmunoassay a clear-cut peak of melatonin concentration was found in the pineal organ of the pigeon at the middle of the scotophase (Coisin et al. 1982a). The aim of the present study was to identify the cell type responsible for the nocturnal indole metabolism, including melatonin synthesis, in the pineal of this avian species. After a short-term incubation or organ culture in the presence of [3H]-indolic precursors, [3H]-5-hydroxytryptophan or [3H]-5-hydroxytryptamine, the relative amounts of deaminated and acetylated products occurring in the pineal organ were measured by the use of thin layer chromatography and liquid-scintillation counting. It was possible to modify the relative amounts of deaminated and acetylated indoles by the application of some inhibitors of monoamine oxidase and cyclic nucleotide phosphodiesterase. Irrespective of the experimental conditions, high-resolution autoradiography combined with the above-mentioned radiochemical experiments showed that the cells of the receptor line (modified photoreceptor cells) are responsible for indole storage and metabolism, and very probably also for melatonin biosynthesis. The other cell types of the pineal parenchyma did not display significant labeling.  相似文献   

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This 2nd part of our studies shows that the papilla foliata is fully developed in Pan, Cebus, and Macaca; in Prosimians the papilla foliata is well developed in Lemur and Chirogaleus. In Galago crassicaudatus, this papilla is missing. Among 3 individuals of Microcebus, the papilla foliata was differently developed: in 2 cases, the tongue exhibited only 2 on both sides and a very low folia. Taste buds were found in the epithelium of only one side of each folium. In the 3rd case, the folia of the papilla were developed only on one side of the tongue, whereas, on the other side, a typical papilla was missing. Instead of the papilla, the tongue of the same animal exhibited a hillock-like structure; it is a gustatory hillock which exhibited many taste buds. There were 3 gustatory hillocks in all of the specimens of Tupaia glis; they are situated on both sides of the tongue.  相似文献   

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Summary Movements of the maxilla and mandible were recorded during drinking in the head-fixed pigeon and correlated with electromyographic activity in representative jaw muscle groups. During drinking, each jaw exhibits opening and closing movements along both the dorso-ventral and rostro-caudal axes which may be linked with or independent of each other. All subjects showed small but systematic increases in cycle duration over the course of individual drinking bouts. Cyclic jaw movements during drinking were correlated with nearly synchronous activity in the protractor (levator) of the upper jaw and in several jaw closer muscles, as well as with alternating activity in tongue protractor and retractor muscles. No EMG activity was ever recorded in the lower jaw opener muscle, suggesting that lower jaw opening in this preparation is produced, indirectly, by the contraction of other muscles. The results clarify the contribution of the individual jaws to the generation of gape variations during drinking in this species.Abbreviations AMEM adductor mandibulae externus muscle - DM depressor mandibulae muscle - EMG electromyographic - GENIO geniohyoideus muscle - LB lower beak - LED light-emitting diode - PQP protractor quadrati et pterygoidei muscle - PVL pterygoideus ventralis muscle, pars lateralis - SeH/StH serpihyoideus or stylohyoideus muscle - UB upper beak  相似文献   

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Summary The normal microscopic pattern and ultrastructure of the lower trachea and the primary and secondary bronchi of the budgerigar (Melopsittacus undulatus) are described. The trachea is lined by mucociliary pseudostratified columnar epithelium with simple acinar mucous glands; epithelium in primary and secondary bronchi becomes progressively lower and less pseudostratified, and mucous cells less aggregated. The wall structure shows a parallel simplification; tracheal elements are comprised of osseous metaplastic cartilage with bone marrow between cancellous trabeculae, whereas distal secondary bronchial walls are principally comprised of smooth muscle. Mucous cells are similar to those described in mammalian, and other avian respiratory mucosae. Ciliated cells are similar to those known in other avian airways. No brush cells or Clara cells are observed.  相似文献   

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Wood anatomy is one of the tools used for taxonomic classification of species. By combining this tool with molecular phylogeny, the current groupings made in morphological studies can be discussed. This study describes the wood anatomy of the monotypic genera of Cupressaceae and analyses the features that could represent synapomorphies of the principal clades recovered by molecular phylogeny. The wood anatomical study shows the high homogeneity of this family, revealing the presence of common ancestral features that support the union between Taxodiaceae and Cupressaceae s.s. and the separation of Sciadopitys. It also supports the group formed by Taxodiaceae in Cupressaceae s.l. No clear division was observed between the callitroid and cupressoid clades. Some wood anatomical differences were observed in the FitzroyaDiselmaPilgerodendron and MicrobiotaPlatycladusTetraclinis associations. The wood anatomical features common to the family, such as axial tracheids without helical thickenings, homogeneous rays, cupressoid cross-field pits and the presence of a warty layer, are put forward as possible synapomorphies for Cupressaceae s.l. The clade-specific synapomorphies are taxodioid cross-field pits for taxodioid and sequoioid clades, absence of a well-defined torus in ThujaThujopsis and torus extensions in DiselmaFitzroyaWiddringtonia.  相似文献   

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Synopsis The presence of ribonuclease and deoxyribonuclease is reported in human elastic tissue. Differences between the effects of various agents on these enzymes in epidermal cells and in elastic tissue are described. Other acid hydrolases in elastic tissue have also been investigated.It is thought that the presence of these acid nucleases and other hydrolases in elastic tissue may be related to its removal and thus provide the means whereby a dynamic system of breakdown of old fibres and the formation of new fibres is continually occurring in dermal tissues.  相似文献   

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A flattened discoid flagellate collected from the Seto Inland Sea, Japan, has been examined by light and electron microscopy. This alga agrees well withClisthodiscus luteus Carter. It has two heterodynamic flagella emerging from a furrow on the upward side of the cell that contains six to 13 yellow-green parietal chloroplasts. It does not rotate but smoothly glide while swimming. The cell has a thin periplast lying between the plasmalemma and chloroplasts. Neither lipid bodies nor mucocysts are seen in the periplast. The pyrenoid matrix being free from thylakoids is penetrated by several cytoplasmic canals from various directions. There are no vesicles of periplastidal network in the narrow space between chloroplast envelope and chloroplast ER. The ultrastructural features ofO. luteus are unique, sharing certain characters with the raphidophycean algae but others withPseudopedinella pyriformis, a unique member of the Chrysophyceae.  相似文献   

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In the present paper, we describe anatomical variants of the anterior inferior cerebellar artery in man for applicative purposes. Our goal was to provide the surgeon with a detailed anatomical view of the region. This is similar to what he may observe through the surgical microscope using modern microsurgical techniques. We have focused our attention on the segments of the artery comprising its origin, its course until it reaches the cerebellum and its main collateral branches. Our results confirm the great variability of the elements under study, but enable the establishment of a few basic variational patterns. These patterns together with their relative frequency may be helpful in microsurgery.  相似文献   

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During each phase of the pigeon's eating sequence, jaw opening amplitude (gape) is adjusted to the size of the food object; first prior to contact (Grasping), again in positioning the food (Stationing), and finally, during its movement through the oral cavity (Intraoral Transport). Part I of this study examined jaw movement kinematics during ingestion of different size food pellets to determine the relative contribution of velocity and rise time variables. Part II specified the muscle activity patterns mediating each phase of the eating sequence, and determined how these patterns are modulated to produce adjustments of gape size.The relative contribution of velocity and rise time variables to the control of gape differs in each phase of the eating sequence. However, for any pellet size, variations in opening rise time may function in a compensatory manner to minimize gape undershooting. Each phase of the eating sequence is mediated by a characteristic muscle activity pattern. The adjustment of gape size to pellet size involves systematic modulation of this pattern, and the parameters modulated differ in the different phases in a manner which may reflect the functional requirements of each phase.Abbreviations AMEM adductor mandibulae externus muscle - DM depressor mandibulae muscle - EMG electromyographic - PDC/PDR pterygoideus muscle, pars dorsalis caudalis and rostralis - PQP protractor quadrati et pterygoidei muscle - PTP pseudotemporalis profundus muscle - PVL/PVM pterygoideus ventralis muscle, pars lateralis and medialis  相似文献   

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The distribution of euphausiids and other macrozooplankton wasinvestigated in and around the Kuroshio front formed in theKa.shima-nada Sea. Japan. during the summer of 1993. Zooplanktonwere dominated by copepods, chaetognaths and euphausiids. andtheir biomass was significantly higher at the frontal stations.Eighteen species belonging to six genera of euphausiids werecollected. The species composition and community structure ofeuphausiids changed drastically with the ‘areas’corresponding to the hydrological conditions. In the area underthe influence of the Kuroshio. most euphausiids were warm-waterspecies. In contrast. euphausiids found in the frontal areawere those usually predominating in subarctic or cold Oyashiowaters. In the area of the warm water tongue. where warm Kuroshiowater lay above cold Oyashio water, the species compositionof euphausiids represented a mixture of both warm- and cold-waterspecies. Surface aggregations of Euphausia pacifica were observedin the frontal area during the night. The biomass and densityof the aggregations ranged between 90 and 136 mg C m–3and 164 and 238 md. m–3 respectively. These aggregationswere mostly made up of immature individuals of < 12 mm. Passivetransportation by convergent flow at the front seems to explainthe observed surface aggregations of E.pacifica.  相似文献   

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Species of Valerianaceae are a common component of the alpine flora throughout the Northern Hemisphere as well as the Andes of South America. Sequence data from three chloroplast markers (psbA-trnH intron, trnK-matK intron, and the trnL-F region) along with the internal transcribed spacer region (ITS) of nuclear ribosomal DNA were used to infer relationships within Valerianaceae. Both genomes, as well as a combined data set, provide support for the major clades within the group and do not support a monophyletic Valeriana. In addition, these data indicate that Plectritis is nested within South American Valeriana, as opposed to being sister to Centhranthus as previously hypothesized. Valerianaceae appear to have originated in Asia, probably in the Himalayas, and subsequently to have dispersed several times to Europe and to the New World. Our results imply that Valerianaceae colonized South America on multiple occasions from the north. In one of these cases there appears to have been a substantial and rapid radiation, primarily in the high elevation paramo habitat. A variety of methods were used to estimate divergence times to determine when Valerianaceae might have colonized South America. Regardless of the method and fossil constraints applied, our estimates suggest that Valerianaceae colonized South America prior to the formation of the Isthmus of Panama.  相似文献   

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