The ontogenesis of monoaminergic nerve fibres in the hypophysis of Rana temporaria with special reference to the pars distalis.

In Rana temporaria tadpoles, fluorescent fibres appear in the prospective eminentia mediana, the pars intermedia and the pars distalis at Gosner's stage 25. During prometamorphosis the amount of fluorescent material increases around the developing primary capillary plexus in the eminentia mediana. In the pars intermedia the fibres form a dense fluorescent network but in the pars distalis the fibres are few and delicate. At stages 42-43, the onset of climax, the pars distalis fibres disappear. The possible functional significance of the pars distalis fibres is discussed. The background adaptation ability appears at stages 28-29, while the fluorescent pars intermedia innervation is observable at stage 25.