ENThe article deals with the etymological analysis of the mythonyms Barstucke and Marcopole found in the Yatvigian book. The etiology of the Baltic and other IE mythologemes is justified by the diversification of the authentic and innovative (i.e., late) ethno-mythological features predetermined by the convergential process. To summarize the outcomes of the research into the West Baltic (Yatvigian) mythonyms Barstucke and Marcopole, the following conclusions are proposed: 1. The mythonym Barstucke might be ascribed to the cultural borrowings from the West Slavic area, i.e. Pol. dial. bajstruk / bastruk ‘an evil spirit that resides under the roots of the elder’, presupposing the emergence of W. Balt. *bastrukas ‘dwarf ’, which was changed to W. Balt. *barstukas ‘ditto’ due to the metathesis of the sonant. 2. The Yatvigian mythologeme Markopolan / Marcopole ‘terrestrial beings i.e., dwarves / Erde leute / Subterranei dicti (gentlefolk / Edelleuthe)’ reflects morphological structure of a compound of the karmadhāraya type, i.e. W. Balt. dial. (Yatv.) *markā-palā ‘soaked / flattened corn’, which presupposes reconstruction of the sememe *‘mythological being, responsible for the good quality of corn’ performed on the basis of antonomasia change. 3. The names of the dwarves Barstucke and Marcopole recorded in the Yatvigian book are to be regarded as synonyms. [From the publication]