Abstract
1. Administration of a 0.025% solution of thiourea to tadpole of Rana temporaria prevented metamorphosis and produced a definite hypertrophy in the thyroid gland as well as in the hypophysis. Histological changes observed in the affected glands correspond in general to those reported by previous authors, but they persisted intact for more than 6 months of treatment.
2. Treatment with 0.1% or 0.2%o solution of the same drug produced in tadpoles of Rana temporaria a relatively high percentage of hermaphroditic males whose testes contained various numbers of young ova.
3. Treatment with a 0.025% solution produced a marked excess of males. Statistical treatments show that sex reversal from female to male has occurred in this group of experimental animals.
4. Germ cell differentiation in the gonads of treated animals proceeded far ahead of that in the control animals; in the testes of Rana temporaria, bundles of spermatozoa were observed as early as September of the first year. Larvae of Hynobius lichenatus also exhibited an accelerated differentiation of germ cells in both males and females.
