[Brain organization of Amia, Lepisosteus and Polypterus: comparative morphology and quantitative analysys].

The quantitative study of the brain of Amia, Lepisosteus and Polypterus leads to results which are compared to those previously got on the Sturgeon and three species of Tleosts (the Rainbow Trout, the Carp and the Ballan wrasse). The volumetric analysis has been applied at first to the whole brain (encephalization indices) and later to the main subdivision of the brain: telencephalon, diencepahlon... (relation indices and relative volumes). Some result are discussed in regard to the various opinions expressed about the phylogenetic affinities of the studied species. According to the brain organisation, the Bichir (Polyterus) seems to be at a relatively high level of evolution, and no relationship can be expected with the Chondrosteans. Amia and Lepisosteus show a common general brain pattern, but some peculiarities allow to consider Amia as more primitive than Lepisosteus--although the osteological characteristics and the scale structure lead to put together the first one and the Teleosts.