How did zacharias janssen contribute to the cell theory?

Zacharias Jansen (c. 1580 - c. 1638) was a Dutch spectacle-maker credited with inventing the first microscope. By the end of the seventeenth century, further developments by Anton van Leeuwenhoek and Robert Hooke allowed Jansenâ??s microscope to be expanded on and this led to the observation of cells under a microscope.