The topographic pattern of nervus terminalis ganglion cells has been studied in 51 species of Teleosteans. Evidence has been shown of the correlation between the morphology of the rhinencephalon and topographic distribution of nervus terminalis ganglion cells. In the species which have the olfactory bulb closely connected to the nasal sac the ganglion cells are localized among the primary olfactory fibres, next to the glomerular layer. On the contrary in the species which have the olfactory bulb connected to the cerebral hemisphere the ganglion cells show a variable degree of migration towards the caudal part of the bulb. The probable reason of these differences has been discussed, as related to the systematic position, to the size of the individual animal or to the size and the growth rate of the species.