Le système nerveux des cténaires

Summary Ultrastructural evidence is given of the occurrence of nervous elements in the mesoglea of Ctenophores based on the presence of the typical synapses of this phylum.In Beroids, nervous fibers from the ectodermal nerve-net cross the epithelial basal membrane and run through the mesoglea; they are devoid of any ensheathing cell. These neurites build highly differentiated synapses upon the muscles and upon peculiar cells, tentatively named mesenchymal cells.In Cydippids, nerve fibers and nerve cell-bodies have been observed in the mesoglea of the tentacles. The mesogleal core of each tentacle contains mesenchymal cells and a thick strand of neurons and neurites, forming a kind of elongated ganglion. Neurites of either the axial neurones or the epithelial nerve-net neurones form numerous radial nerve strands across the tentacular muscles. Interneural, neuro-muscular and neuro-mesenchymal junctions are very frequent in the tentacle.As far as the organization of the mesoglea is concerned, the Ctenophora thus appear closer to Turbellaria than to Cnidaria.

Ce travail a bénéficié de la collaboration technique de Madame J. Amsellem que nous remercions vivement.     

Le role des “sphagnetalia” dans la vie des tourbières des Hautes-Fagnes

Sans résuméReçu par la rédaction la 1.X.1953.     

Contribution à l'analyse des structures forestières 1. Le grain des dominances

A method of simultaneous analysis of vertical and horizontal structure is described. It is particulary applicable to forest and shrubland. Data come from point-height analysis of vegetation: 100 sample points are arranged in 4 lines of 25, with 2 m between lines and 1 m between points on lines. At each point, specific lists of spaces intercepted optically are observed by vertical measurement strata. Strata depth is 10 cm when mean vegetation height is lower than 4–5 m, and 50 cm above this height. This study is based on height of upper vegetation presence, and applied to low forests ofNothofagus antarctica (Forest.)Verst. in Southern Chile and Argentina. The authors summarize the data sequence by the cumulative sum technique. This technique allows the rapid and clear delimitation of three dimensional mosaic units of vegetation whose height varies vertically from the mean height. The pattern of these mosaic units is shown as three dimensional block diagrams, giving a good representation of structural dominance patterns.     

Le modèle triadique des aspects neurobiologiques des comportements motivés à l’adolescence

Background

Risk-taking behavior is a major cause of morbidity and mortality in adolescence. In the context of decision theory and motivated (goal-directed) behavior, risk-taking reflects a pattern of decision-making that favors the selection of courses of action with uncertain and possibly harmful consequences. We present a triadic, neuroscience systems based model of adolescent decision-making.

Method

We review the functional role and neurodevelopmental findings of three key structures in the control of motivated behavior, i.e., amygdala, nucleus accumbens and medial/ventral prefrontal cortex. We adopt a cognitive neuroscience approach to motivated behavior that uses a temporal fragmentation of a generic motivated action. Predictions about the relative contributions of the triadic nodes to the three stages of a motivated action during adolescence are proposed.

Results

The propensity during adolescence for reward-novelty seeking in the face of uncertainty or potential harm might be explained by a strong reward system (nucleus accumbens), a weak harm avoidant system (amygdala) and/or an inefficient supervisory system (medial/ventral prefrontal cortex). Perturbations in these systems may contribute to the expression of psychopathology, illustrated here with depression and anxiety.

Conclusions

A triadic model, integrated in a temporally organized map of motivated behavior, can provide a helpful framework that suggests specific hypotheses of neural bases of typical and atypical adolescent behavior.     

Le phénomène de superparasitisme chez les parasites oophages des punaises des blés

Résumé L'étude du superparasitisme chez les parasites oophages desAelia a été réalisée avec 3 espèces d'Ooencyrtus: O. fecundus Ferr. & Voeg.,O. nigerrimus Ferr. & Voeg., etO. telenomicida Vass. Ces 3 espèces apparaissent comme ayant un pouvoir de discrimination leur permettant d'éviter le superparasitisme lorsqu'elles ont suffisamment d'h?tes à leur disposition. Dans le cas contraire ou lorsque le nombre de femelles dans un même tube de ponte s'accro?t, la tendance au superparasitisme augmente. Le superparasitisme se traduit par une baisse de la fécondité, une diminution de la taille et une modification du taux sexuel de la descendance.

---

Summary The study of superparasitism in the oophagous parasites of theAelia spp has been realized with 3Ooencyrtus species:O. fecundus Ferr. & Voeg.,O. nigerrimus Ferr. & Voeg. andO. telenomicida Vass. These 3 species appeared to have a discriminating ability which enable them to avoid superparasitism when the host population at their disposal is sufficient. In the opposite case or, when the number of females increases in the same tube, superparasitism tends to increase. Superparasitism results in a decrease in fecundity as well as in size and the sex-ratio of the offspring.

     

Le “Rob de Laffecteur”: un célèbre remède antisyphilitique aux temps des charlatans

The history of “Rob de Laffecteur”, a very popular remedy for a long time due to the confused theories concerning syphilis, reflects the backward thinking in the field of venereology, even up until the second half of in the 19th century, as, in 1858, twenty years after the discoveries by Philippe Ricord, some venereologists still believed in the gonorrhoea and syphilis virus.     

Le Phloème des Cordons Corticaux duViscum album L. (Loranthacées)

Résumé Les cordons corticaux duViscum album L. (Loranthacée) sont étudiés en microscopie photonique et électronique. La présence d'un tissu phloémien comprenant des cellules criblées et des cellules compagnes est, pour la première fois, démontrée. Les éléments criblés sont anucléés, pauvres en cytoplasme dégénérescent et possèdent des plages criblées avec des pores obstrués par des P-protéines. Par contre, les cellules compagnes ont un noyau volumineux et un cytoplasme dense. Ces caractéristiques ultrastructurales sont comparées à celles décrites dans le phloème des plantes autotrophes. Chez les Phanérogames parasites, la différenciation d'un véritable tissu phloémien semble liée au degré de parasitisme qu'elles ont atteint.

---

Phloem in the cortical strands ofViscum album L. (Loranthaceae)

Summary The cortical strands ofViscum album L. (Loranthaceae) were investigated at the light and electron microscopic levels. The occurrence of phloem in its endophytic system is registered for the first time. It consists of sieve tubes and companion cells. The former are enucleated cells with degenerescent cytoplasm, sieve plates and P-protein occluding the pores. The companion cells possess a large nucleus and a dense cytoplasm. These features are compared with those encountered in the phloem of autotrophic plants. Among the parasitic Phanerogames, the differentiation of phloem seems related to the parasitic level reached by these plants.

     

Le contrôle automatique du flux lumineux dans l'oeil composé des Diptères

In the compound eye of the fly Musca, tiny pigment granules move within the cytoplasm of receptor cells Nos. 1–6 and cluster along the wall of the rhabdomeres under light adaptation, thus attenuating the light flux to which the visual pigment is exposed (Kirschfeld and Franceschini, 1969). Two recently developed optical methods (the neutralization of the cornea and the deep pseudopupil) combined with antidromic and orthodromic illumination of the eye (Fig. 1) make it possible to analyse the properties of the mechanism at the level of the single cell, in live and intact insects (Drosophila and Musca). The mechanism is shown to be an efficient attenuator in the spectral range (blue-green) where cells Nos. 1–6 have been reported to be maximally sensitive (Figs. 4c and d, 5b and 11b). In spite of the fact that the granules do not penetrate into the rhabdomere, the attenuation spectrum they bring about closely matches the absorption spectrum of the substance of which they are composed (ommochrome pigment, dotted curve in Fig. 11b). The dramatic increase in reflectance of the receptors after light adaptation (Figs. 3, 4b, 5a and 11a) can be explained as a mere by-product of the high absorption index of the ommochrome pigment, especially if one takes into account the phenomenon of anomalous dispersion (Chapter 8). The vivid green or yellow colour of the rhabdomeres would thus have a physical origin comparable to a metallic glint. Contrasting with the lens eye in which the pupillary mechanism is a common attenuator for both receptor types (rods and cones), the compound eye of higher Diptera is equiped with two types of pupils adapted respectively to both visual subsystems. A scotopic pupil is present in each of the six cells (Nos. 1–6) whose signals are gathered in a common cartridge of the first optic ganglion. This pupil comes into play at a moderate luminance (0,3 cd/m² in Drosophila; 3 to 10 cd/m² in Musca. Figs 13, 14, 15, 16). A photopic pupil is present in the central cell No. 7 whose signal reaches one column of the second optic ganglion. Attenuating the light flux for both central cells 7 and 8, the photopic pupil has its threshold about two decades higher than the scotopic pupil, just at the point where the latter reaches saturation (Fig. 3b, e-State II of Figs. 6b and 15). The photopic pupil itself saturates at a luminance one to two decades higher still (Fig. 3c, f=State III of Figs. 6c and 15). The two-decades-shift in threshold of these pupil-mechanisms supports the view that receptors 1–6 are a scotopic subsystem, receptors 7 and 8 a photopic subsystem of the dipteran eye. The luminance-threshold of the scotopic pupil (as determined with the apparatus described in Fig. 2) appears to be located at least 3.5 decades (Drosophila) or even 5 decades (Musca) higher than the absolute threshold of movement perception (Fig. 16). After a long period (1 hr) of darkness a light step of high intensity can close the scotopic pupil within about 10 sec (time constant 2 sec as in Fig. 9) and the photopic pupil within no less than 30–60 sec. Some mutants of Drosophila possess only a scotopic pupil (w , Figs. 4 and 5) whereas ommochrome deficient mutants lack both types of pupil (v, cn, see Fig. 7c, d). Comparable reflectance changes, accomplished within about 60 sec of light adaptation, are described for two insects having fused rhabdomes: the bee and the locust (Fig. 17).     

Le monde des morts au Néolithique en Aquitaine : essai de synthèse

This paper proposes to define the main characteristics of the burials and the evolution of funeral behaviours during the Neolithic times, between about 5500 and 2300/2200 B.C., in the present territory of Aquitaine. For the moment, no burial was found for early Neolithic. During the middle Neolithic, about 4500 B.C., appear the first megalithic graves, passage graves (Angoumoisin type) and barrow cists, as well as burial caves. Late Neolithic, between 3700 and 2300/2200 B.C. is the great period of megalithic graves. Single quadrangular dolmen (Caussenard type) were built in Dordogne and in the Entre-deux-Mers in Gironde, gallery graves, the “allées d’Aquitaine” as to the “allées girondines” extended in the centre of the Aquitaine country while in the western Pyrénées the single quadrangular dolmen increased. In return, caves and rock shelter were, it seems to me, less prized by the people during the end of Neolithic times to leave the dead.