Influence of Lead, an Environmental Pollutant on Metamorphosis of Rana utricularia (Amphibia: Ranidae)

The influence of lead, an environmental pollutant on metamorphosis of Rana utricularia, was examined in this study. Larvae of stage XI (Taylor and Kollros, 1946), beginning of the premetamorphic stage, were exposed to lead concentrations of 0.1 ppm, 0.5 ppm, 1.0 ppm and 1.5 ppm for 106 days. The untreated larvae served as controls. Larvae were observed from early limb bud stage, stage X, through the protrusion of the forelimbs, stage XX. Neither the sequence of developmental events nor the gross external and internal morphology was altered by lead. However, lead prolonged the time of metamorphosis by delaying the completion of each successive prometamorphic stage. The extent of delay was concentration dependent. The thyroid gland of the experimental larvae underwent alterations which were also concentration dependent. The size of the gland and the size of the follicle were reduced. Vacuolation occurred in the colloid of both 0.5 ppm and 1.5 ppm lead treated larvae