Abstract
SUMMARY: The appearance of the growth-promoting activity in the cephalic lobe and the caudal lobe of the pars distalis in the chick embryo was investigated by tests on tadpoles. Activity was first found in the caudal lobe of the chick embryo after incubation for 15 days. No growth-promoting activity could be demonstrated in the cephalic lobe, which, on the contrary, had a significant inhibiting effect on the weight gain of tadpoles when obtained before the 15th day of incubation. The appearance of growth-promoting activity in the caudal lobe coincides with the appearance of the so-called A1-cells in this lobe.