[Effect of the post-retinal fibres on the growth of the optic lobe in the larva ofAeshna cyanea Müll. (Insect, Odonata)].

Since to earlier results indicated a dependence of the optic lobe on the compound eye during post-embryonic development, it appeared essential to specify the part played by the post-retinal fibres connecting these two organs. Especially, we wondered if the mitotic activity in the outer optic anlage common to the two outer optic ganglia (lamina and medulla) was controlled by the number of newly-neoformed post-retinal fibres, or if the regulating influence from the post-retinal fibres takes place later, during the differentiation of the ganglion cells.In order to answer these questions, three kinds of operation were performed: (1) removal, in young larvae, of the zone producing new ommatidia. This operation deprives the optic of the arrival of new post-retinal fibres below the operated level. (2) overloading of post-retinal fibres, by inducing zones that produced supernumerary ommatidia. (3) removal of an ocular volet, followed by its immediate reinsertion, to provide a "surgery-control". The following results were obtained: (1) A preliminary growth regulation controlled the total number of neuroblasts in the outer optic anlage. However, the permanent mitotic activity of these cells was not controlled by post-retinal fibres. (2) A second regulation, much more precise, occurring in the lamina, consisted in the differentiation of the ganglion cells being affected by the new post-retinal fibres. The supernumerary cells then rapidly degenerated. (3) A last regulatory process, implying the integrity of post-retinal fibres, maintained the ganglion cells.