The scientist most likely to have studied tadpole cells under a microscope is Hooke. Robert Hooke is known for his pioneering work in microscopy and is credited with the discovery of cells. Although he primarily studied cork cells, he was one of the first to use a microscope to observe and describe various biological specimens.
While Schwann, Schleiden, and Janssen made significant contributions to cell theory and microscopy, Hooke's work was foundational in the field of cell biology.