The paper aims at identifying the connection between the target domain and the source domain (represented by the PARTS OF MECHANISM, MECHANISM REPAIR, MECHANISM ACTIVATION). The author uses continuous sampling method, as well as methods of conceptual and component analysis, in order to elicit multiple target domains and the mapping principle. The sentences under research (512 metaphorical expressions) were taken from various British and American popular science journals on Biology. The author considers the key works written in the field of conceptual metaphor (G.