AbstractIn the skate,Raja radiata, the nerve fibres of the hypophysial stem, which connects the hypothalamus with the neuro‐intermediate lobe, are arranged with a median neurosecretory tract and lateral, presumably adrenergic, tracts. Transecting the median tract usually did not affect colour change,i.e.there was normal control of MSH secretion, whereas lesions in the lateral parts usually led to darkening,i.e.uninhibited MSH release. Deviations from this scheme in the present experiments and in the literature are easily explained by assuming slight anatomical variations in the ste