The midbrain growth of an aquatic Anuran (Xenopus) develops as in an Urodelan (Triturus): in both aquatic Amphibians the growth rate and the mitotic ratio of the midbrain are correlated and show two peaks of activity, one at the end of the embryonic life and one in the larval life, without maintaining the rate at the end of the metamorphosis as in a terrestrial Anuran (Bufo). Therefore the growth and the mitotic activity of the midbrain are ruled by ecological factors. The midbrain development of the aquatic Anuran having the same features as the terrestrial one, it is suggested that the ecologic factors are unable to influence the acquired nervous functions of a phyletic group. A seat of active morphogenesis is the ependymal crescent along the posterior pouch of the mesencephalic vesicle which supplies first the increase and thickening of the roof and then the growth of the tori semicirculares.
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Con il contributo del Ministero per i Beni e le Attività Culturali