Caractères physico-chimiques des choanoleucocytes de quelques Invertébrés

Sans résumé     

Les premiers vertébrés et les premières étapes de l’évolution du crâne

The earliest vertebrates and the first steps of the evolution of the skull. Vertebrates are one of the few metazoan taxa, which display a well-corroborated phylogenetic pattern, a good and anatomically informative fossil record, and a relatively slow ontogenetic development. They are thus a favourite taxon for illustrating evolution as a historical process, although the stem of the vertebrate tree remains poorly documented by fossils, except for some Early Cambrian forms. Therefore, the characterization of the vertebrates now rests essentially on a small number of developmental characters, mostly involved in the rise of the skull, and whose precursors may occur in other chordates. The tree of the crown-group vertebrates also shows some major morphological gaps due to early extinctions, but a number of Palaeozoic stem gnathostome taxa helps in documenting the agnathan-gnathostome evolutionary transition. However, stem cyclostomes remain elusive.     

Premières données sur les Ostracodes du Cénomanien deYougoslavie (istrie du sud)

enAn Upper Cenomanian Ostracode assemblage has been identified near Premantura, South Istria (Yougoslavia), in an internal carbonate platform deposit. This appears of peculiar interest because of lack of datas concerning this area during the Cretaceous. Systematical studies are proposed and two new species erected: Rehacythereis apulicus nov.sp and Perissocytheridea istriana nov.sp. Some attempts are given upon paleoenvironments and paleobiogeographical signification.     

Contribution à l'analyse des structures forestières 2. Caractérisation et analyse du toit de la végétation

Data used come from point-height analysis. 100 sample points are arranged in 4 lines of 25, with 24 m between lines and 1 m between points on lines. At each point, vertical lists of species are compiled, by measurement strata. Such strata depth is 10 cm when mean vegetation height in the stand is lower than 4–5 m and 50 cm when heigher. A synthetic vegetation profile is obtained by sum of species presences in each measurement stratum for all 100 observations. When these profiles are bimodal, vegetation can be divided in two at the secondary minimum level: the upper part is the canopy, the lower the understorey. Only the canopy structure is dealt with in this tudy. Several parameters, describing vertical structure of woody vegetation, are defined and measured. They are: (1) maximum height, (2) upper and lower canopy limits, (3) canopy depth and (4) density. Delimitation of canopy is achieved by calculating the hypegeometric probability of realisation groups of vegetation presence, or absence, in the vertical line of sight. The thickness is the difference between the two previous values (2) and (3) and density the number of intercepts between them. Horizontal variations in those structural parameters are revealed by cumulative sum method which demonstrates different types of pattern. Relations between horizontal variations are studied by pairs; actual values compared by linear correlation analysis while concordance between patterns are characterised by the coefficient of simple concordance ofSokal etMitchner and by a binary autocorrelation coefficient.Shannon's formula enables an overall appreciation of canopy homogeneity. an example is applied to some stands ofNothofagus antarctica (Forest) Verst. in Southern Chile and Argentina. The upper canopy limits are the same upper vegetation intercepts so canopies are smooth. High correlation exists between upper and lower limits of the canopies, and low correlation between the latter and thickness and density, so canopies are uniform.     

Micro-organismes de type mycoplasme chez les Coléoptères

Résumé Des micro-organismes présentant les caractères des mycoplasmes ont été observés dans les tissus adipeux et cardiaques de larves du Coléoptère ScarabeideMelolontha melolontha, soit sur des tissus prélevés directement sur larves, soit maintenus en culture d'organes pendant 15 jours à 3 semaines.

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Summary Microorganisms with characteristics usually observed in mycoplasms when examined under the electron microscope have been seen in fat and cardiac cells from larvae ofMelolontha melolontha, [Scarabaeidae Coleoptera]. These observations have been made either on tissues taken directly from larvae or kept in organotypic culture for 15 days to 3 weeks.