METAMORPHOSIS AND NEUROSECRETION OF XENOPUS LAEVIS.

Abstract

ABSTRACT The metamorphic climax of Xenopus laevis tadpoles was inhibited by treatment with thiourea in a concentration of 0.1 per cent in aquarium water. After 1, 3, 4, 5 and 7 months, two tadpoles were killed and fixed, and another two transferred to thiourea-free water. When the last-mentioned tadpoles reached the height of metamorphic climax they were killed and fixed. Observations were made on the histology of the hypothalamo-pituitary neurosecretory apparatus at different time intervals before and after metamorphosis. The secretory activity of the cells in the praeoptic nuclei was estimated by counting the relative frequency of cells showing neurosecretion, as well as the nuclear volume of the cells in the praeoptic nuclei. Prolonged treatment with thiourea did not alter the gross morphology of the hypothalamic neurosecretory system. When the tadpoles were allowed to metamorphose by withdrawing the thiourea, the number and the nuclear volume of the cells showing neurosecretion increased in the praeoptic nuclei, thus suggesting augmented secretory activity.