Abstract
The circulating blood of Rana catesbeiana tadpoles which are undergoing metamor-phosis contain both tadpole and adult frog hemoglobin. The appearance of frog hemo-globin in the blood of animals during metamorphosis can be followed by determi-nation of the reactive sulfhydryl groups in the blood for these are only present in frog hemoglobin. The time required for the complete molecular change from tadpole hemoglobin to frog hemoglobin is approxi-mately seven to eight days.
The authors wish to express their thanks to Dr. K. Kaziro for his advice. This work was supported by a Grant for Scientific Research from the Ministry of Education of Japan.
