The process of labyrinth determination has been studied in three urodelean and seven anuran species by means of homoplastic transplantation of ear region epidermis, defined as the piece of epidermal layer containing the material of the prospective ear vesicle (labyrinth rudiment). The ear region epidermis was grafted onto the abdominal wall of embryos of the same developmental stage. The earliest stage of operation resulting in ectopic ear vesicle formation was determined, suggesting the appearance of organ-specific properties in the ear ectoderm. These properties were enhanced in the further course of development, as indicated by the frequency of ear vesicle formation and by the volume and degree of complexity that the vesicles reached. The data obtained allowed us to arrange the species studied in a sequence, ranging from most Ranidae and Bufo viridis, in which organ-specific properties appear earlier and are most strongly expressed, to Triturus vulgaris in which their expression is least pronounced. Comparison of properties of the material giving rise to the ear vesicle or to several other ectodermal derivatives led to the conclusion that species-specific differences in determination of different ectodermal rudiments are due to species specific properties of the whole ectoderm. These differences appear to be determined by an evolutionary shift of the beginning of gastrulation towards later cleavage cycles.