The effects of metopirone and aldactone on the histology of the pars distalis of the pituitary, the interrenal gland and the interstitial tissue of the testis were studied in male common frogs. Activation of the interrenal tissue by these substances was paralleled by a stimulation of one of the tinctorial cell types in the distal lobe namely the basophils 3 and of caudal chromophobic cells. Simultaneously a regression of the interstitium testis was observed. It is suggested that either the basophils 3 or the caudal chromophobic cells have a corticotropic function.
I wish to express my gratitude to Dr. W. J. van Dongen for enabling me to do this work in his Institute and for his helpful criticism, and to Prof. Dr. P. G. W. J. van Oordt for his encouragement, especially in the study of the pituitary gland. Thanks are also due to Prof. Dr. D. Lacy for reading the manuscript, and to Miss Mieke Roelofsen for her conscientious technical assistance.