Bufo arenarum ovulations have been kept in potassium bibasic arsenate from the fertilization until 26mm larva. The gonad in development, in the presence of the toxic, suffers significant alterations in its volume, shape and structure. It does not have the typical naillike morphology; on the other hand, it is presented as a spherical mass of reduced volume, that has, as demostrated by the histological analysis, very few oocytes or gonia submerged in a very scarce quantity of stroma. The hypothesis of this study was that it would be due to a succession of events whose cause would lie on the damage that the arsenic determine at the somatic layers level.