The extirpation of the hypophysjs in the adult frog has not given uniform results. Caselli ('00) and Gaglio ('02) who reported no changes following hypophysectomies were followed by Boteano ('06) who reported a neuromuscular asthenia in the operated animals. Houssay ('10) came to the conclusion that the removal of the gland was followed by death. Adler ('14) burned out the hypophysis of a 20 mm. Rana temporaria larvae with the electric cautery. Out of the 1200 operated animals three were found to have been hypophysectomized, not, however, without great injury to the surrounding soft parts, particularly the brain. In not one of those three animals did hjnd legs develop beyond a small bud, and transformation did not take place, the specimens remaining as neotonic tadpoles.
This work was commenced in the Spring of 1914, repeated in 1915, and again in 1916, Diemyctylus torosus, Rana pipiens, and Rana boylei being successively used. In this paper the results obtained with the California yellow-legged frog, R. boylei are reported. Shortly after the closure of the medullary plate, Kopsch's stages d-e, was found to be the size in which the hypophysial invagination could be most successfully removed. About 200 larvae of this stage were operated upon. I n specimens of this size the hypophysis was successfully removed in over 60 per cent of the operated animals. Approximately 30 per cent of those animals in which the gland was extirpated did 57