Olivier Perru

Analyser les origines de l'apparition du concept de zoonite comme unité d'organisation segmentaire en zoologie demande de se placer dans le contexte de la première moitié du dix-neuvième siècle, plus spécifiquement vers 1826-1839. Si les origines de la problématique remontent à Goethe, d'une part, à des botanistes tels que de Candolle d'autre part, la thèse de Moquin-Tandon sur les dédoublements chez les végétaux (1826) est une étape essentielle. Les hypothèses de multiplication et de diversification des organes arrangés selon une symétrie, préside aussi à ses recherches sur les Hirusinées (1827). Le zoonite est une unité organique élémentaire pouvant se démultiplier et il est structuré symétriquement. Mais, ce qui le caractérise est sa composition lui conférant une autonomie. En 1832, Dugès regardera le rapport entre zoonite et organisme total sous l'angle de la conformité organique. Il déduit de ses observations les lois de multiplicité des organismes, de disposition, de modification et de coalescence. Cette dernière loi deviendra primordiale chez Dugès en 1838 pour expliquer l'évolution de l'être composé ainsi que la croissance embryonnaire. Mais, le zoonitisme des années 1830 ne constitue pas une théorie scientifique, même s'il servira ultérieurement de référence, en particulier dans la physiologie animale d'Edwards. To analyse the origins of the appearance of the zoonite concept as a unit of segmentary organisation in zoology requires positioning oneself in the context of the first half of the nineteenth century, more specifically in the years 1826-1839. If the origins of the problem go back to Goethe, on the one hand, and to botanists such as de Candolle on the other, the thesis of Moquin-Tandon on the splitting of plants (1826) is an essential step. The hypotheses of multiplication and diversification of organs arranged according to a symmetry, also presides over his research on the Hirudinées (1827). The zoonite is an elementary organic unit which can multiple itself and is structured symmetrically. But what characterises it is that its composition confers on it a certain autonomy. In 1832, Dugès regarded the connection between zoonite and total organism from the angle of organic conformity. He deduced from his observations the laws of multiplicity of organisms, of disposition, of modification and of coalescence. This last law would become vital to Dugès in 1838 for explaining the evolution of the composed being as well as embryonic development. But zoonitism in the 1830s did not constitute a scientific theory, even if it would ultimately serve as a reference, in particular for the animal physiology of Edwards

Our paper focuses on the theory of bud’s development in some works of the french botanist Aubert A. du Petit Thonars (1758–1831). From 1792 to 1801, he was a botanist traveller, visiting Tristan d’Acugna, Le Cap, Madagascar and L’Isle Bourbon, and he observed the growth of tropical trees. He concluded that, on the bark, many buds produced some bundles of fibres. He repeated his observations and experiments with European trees in France. For him, the bud’s activity produces fibres. Collections of fibres cause a organic unity. Du Petit Thouars carried on with the studies of Duhamel du Monceau about wood and bark. He discovered that these two vegetal tissues were independent, but grew from the same matter, which was called “cambium” by Duhamel du Monceau in 1758. Our botanist’s opinions and observations were discussed and his point of view was sternly combatted by the French physiologist Brisseau-Mirbel, but it was taken up again by Moquin-Tandon. Finally, the cellular theory and discoveries of vegetal tissues proved Brisseau-Mirbel right about building up of plants: they are made up of cells but they are not a composition of fibres.

Résumé Dans cet article, nous examinons la Démonstration de l’existence de Dieu de Fénelon ; la question posée est celle de la démarche apologétique, où le spectacle de la nature donne à voir l’activité du Créateur. Dans un regard qui suppose la foi, Fénelon met en relation le caractère admirable de l’ordre du monde et ce Dieu que nul ne conteste encore sérieusement. Réenchantant l’univers mécaniste, Fénelon en appelle à un Dieu seul capable de mettre en harmonie le mécanisme et la vie ainsi que le corps et l’âme. À la lumière de la science du temps, les espèces animales s’inscrivent dans un ordre équilibré et vivant, le corps organisé est le siège d’opérations d’assimilation et de génération, inaccessibles à la machine, il semble aussi fournir le support des pensées à l’âme. Faute de l’existence d’une cause assumant simultanément les dimensions matérielles, vitales et spirituelles, le lecteur se trouve renvoyé à l’action divine. S’agit-il ici d’occasionalisme fénelonien? Peut-on parler de postérité de Fénelon dans le discours sur la nature au xviii e siècle?

The aim of this paper is an epistemological analysis of mutualism modeling. From the Lotka-Volterra analysis, we look for some characteristics and epistemological inadequacies of this class of models. Volterra s’mathematical work was a response to a particular ecological situation. This situation is the rupture of the equilibrium between competing associated species. Starting from equations describing variations in competing populations, a change of sign is enough to transform them into equations describing variations in numbers of mutualistic populations. In terms of modeling, competition models have attracted a lot of attention while mutualism has been relatively neglected. If the relative growths of the two populations are the same, applied to mutualism Lotka-Volterra models indicate an equilibrium point. These models are used to make a distinction between obligatory and accidental mutualism. To be considered valid these models need to give an equilibrium point and provide the dominant characteristic of biological mutualism (obligatory or accidental). From the end of the 90s, some researchers have developed more realistic bio­logical models that allow a transition from parasitism to mutualism depending on the densities of the two partners. From an epistemological viewpoint, these models remain relative to a population level. They refer to the biological pop­ulations studies but they need to be complemented by an analysis of the same biological phenomenon at an individual level.