THE EFFECTS OF THIOUREA AND PHENYLTHIOUREA UPON THE DEVELOPMENT OF ELEUTHERODACTYLUS RICORDII

Abstract

Eleutherodactylus is unlike most anurans in that it possesses no aquatic larval stage. Its eggs are terrestrial and the young toads attain the adult body form before hatching. In an attempt to ascertain to what degree the suppression of larval characters and the early assumption of adult body form are dependent upon thyroid activity, eggs were raised in solns. of thyroid-inhibiting drugs. Embryos placed in .05% thiourea or .005% phenylthiourea on the 5th day of development failed to attain complete limb differentiation and retained the larval tail, while tap-water controls differentiated normally and lost the tail at the same time as did controls raised in air. Animals raised in .005% thiourea exhibited no retardation in limb development but did retain the tail. Treatment with .001% thiourea was ineffective. Thyroids of animals raised in .05% thiourea or .005% phenylthiourea showed marked hyperplasia, hyperemia and colloid reduction; those of .005% thiourea-treated animals were less strikingly affected. It appears that, in Eleutherodactylus, loss of the larval tail and complete differentiation of limbs are features which are under thyroid control. However, suppression of many of the larval features cannot be attributed to thyroid activity since it occurs even under conditions of extreme thyroid inhibition. The embryos raised in .005% phenylthiourea showed a rapid loss of pigment which involved not only the skin but also the pigmented coat of the eye. This is probably the result of the well-demonstrated inhibitory effect of this drug upon tyrosinase melanin formation.