The development of the cerebellar dorsal lamina in an aquatic Anuran (Xenopus) proceeding as in a terrestrial Anuran (Bufo), the cerebellar morphogenesis in the Amphibians appears directed by phyletic factors. On the contrary the growth of the methen-cephalon in the aquatic Anuran is similar to that of an aquatic Urodelan (Triturus): in both aquatic Amphibians the mitotic ratio rises till the beginning of the prometamorphic life, then it falls without showing any mitotic rise at the end of the metamorphosis, as it does in the terrestrial Anuran. Therefore the neural growth and its mitotic ratio are directed by ecologic factors.