Étude anatomique du système nerveux central et stomatogastrique de l'Insecte OrthoptèreOrphania scutata (Tettigoniidae)

Résumé L'étude anatomique du système nerveux central et stomatogastrique d'Orphania scutata fut entreprise par les méthodes classiques de dissection. L'aspect et la disposition des masses cérébrales et ganglionnaires sont étudiés ainsi que la disposition et le trajet des nerfs qui en sont issus.Chez le mâle comme chez la femelle, le cerveau, les ganglions thoraciques et le système stomatogastrique présentent la même disposition. Seul, parmi les ganglions de la chaîne nerveuse ventrale abdominale, le dernier ganglion, ou ganglion génital, résulte de la fusion des neuromères 8–9–10–11, et présente des particularités liées au sexe.

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Summary The study ofOrphania scutata was undertaken through classical dissection methods. Aspect and arrangement of brain and ganglia, as well as setting and direction of nerves emergence, have been studied.In male as well as female, brain, thoracic ganglia and stomatogastric system show the same disposition. Among the ganglia of the ventral nerve cord, the last one or genital ganglion presents modifications in male as well as in female.

     

Étude du contrôle neuro-endocrine du fonctionnement du corpus allatum chez les larves du quatrième stade de Rhodnius prolixus

This paper concerns the effects of electrocauterization of the pars intercerebralis (P.I.) in the penultimate instar (fourth) of Rhodnius prolixus performed at various intervals following a blood meal. The following ecdysone-induced apolysis is strongly adultoid in the larvae whose P.I. was destroyed within 20 hr after a meal. The same operation at 24 hr, 48 hr, and 7 day intervals accompanied with ecdysone injections does not produce such effects since the resulting cuticle synthesis is normal (larval). These experiments demonstrate that the protocerebrum has an allatotropic action during the 20 hr following the blood meal. The stimulation of the corpus allatum is effected by a humoral pathway as shown by experiments of disconnecting C.A., cauterization of the P.I., and the application of juvenile hormone. Allatotropic and prothoractotropic effects of the brain cannot be induced by implanting entire brains or only P.I. The results of parabiosis between a fed allatectomized insect and a parsectomized one just after a meal do not allow us to evaluate the allatotropic effects as the apolysis does not occur in such pairs.These results have permitted us to discuss the secretory activity of the brain and its interactions with other endocrine glands.     

Altération du système membranaire de protoplastes de feuilles de piment (Capsicum annuum) sous l'action du capsidiol

During infection with Phytophthora capsici, we demonstrated that susceptible induced pepper leaves produced apposition walls that protect host cells, but modifications perturbed the photosynthetic apparatus and crystal-like structures appeared in chloroplasts. We propose that these alterations may be due to the action of capsidiol synthesized by host cells. To confirm this hypothesis, we tested the action (1 h) of capsidiol (400 μg.mL⁻¹) on isolated leaf protoplasts and we observed the formation of crystal-like structures on the site of clustered thylakoïds. The destructuration is initiated by the deposition of a proteic osmiophilic substance within the lumen of each thylakoïd, then the process was extended to the other thylakoïds in the same group. Thus, a transversal arrangement progressively occurred and served as substitute for the initial vertical disposition of the membranes. Plasma membrane and cytoplasmic organelles were also altered and we observed that the endoplasmic reticulum was in cluse association with the plasma membrane, probably to play a detoxicating role.     

Commentaires sur le système de classification des angiospermes de takhtajan

The authors analyze Takhtajan's system of classification of the Angiosperms in relation to the principles of evolutionary and cladistic systematics. It is shown that Takhtajan belongs to the evolutionary school: he identifies the ancestors of some taxa, he accepts polytomous branching and he groups taxa on the basis of primitive as well as derived character states. Takhtajan's notion of weighted similarity does not appear to be based on objective criteria, when determining the weight and evolutionary status of characters.After a summary of the modifications brought out by Takhtajan in his 1980 version, the weak and strong points of evolutionary systems as a whole are emphasized. In these, the delimitation of taxa and their filiation are difficult to refute since they do not rely on precise criteria, which would ensure continuity and uniformity within a given system. However, these systems have some flexibility, which allows them to incorporate readily new information, a feature unfortunately missing in cladistic classifications. In fact, while it does have weaknesses from a theoretical point of view, the system of Takhtajan gives us an idea of flowering plants phylogeny that appears to be one of the most complete at the present time from both analytical and synthetic standpoints.

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Commentaires sur le système de classification des angiospermes de takhtajan

Résumé Les auteurs analysent le systeme de classification des Angiospermes de Takhtajan en fonction des principes de la systematique evolutive et de la systematique cladistique. Il est démontré que le systeme de Takhtajan appartient a l'école evolutive: cet auteur reconnait directement les ancêtres pour certains taxons; il accepte des embranchements polytomiques dans ses dendogrammes et, enfin, il réunit les taxons aussi bien sur la base de caractères évolués que primitifs. La notion de similarités pondérées de Takhtajan ne semble pas basée sur des criteres objectivs pour determiner le poids et le stade évolutif des caractères.Après avoir resume les modifications apportées par Takhtajan dans la version de 1980, les auteurs font ressortir les faiblesses et les points forts des systemes evolutifs en general. Dans les systemes evolutifs, la delimitation des taxons et leur filiation sont difficilement réfutables puisqu'ils ne reposent pas sur des criteres precis qui assureraient une continuity et une uniformity a l'intérieur d'un même systeme. D'un autre côté, ces systemes possèdent une flexibility qui les rend aptes a incorporer des changements mineurs apportés par des travaux nouveaux, element qui fait malheureusement défaut a la systematique cladistique. En fait, tout en comportant des faiblesses au niveau théorique, le systeme de Takhtajan nous donne une vision de la phylogénie des plantes a fleur qui, pour le moment, demeure Tune des plus complete tant du point de vue analytique que synthétique.

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