You're likely thinking of Zacharias Janssen and Hans Lippershey, not Hans and Zacharias. While they are not directly credited with contributions to cell theory, their invention of the compound microscope played a crucial role in its development.

Here's how:

* Zacharias Janssen and Hans Lippershey are both credited with inventing the compound microscope around 1590. This invention allowed scientists to see objects that were too small to be seen with the naked eye.

* Robert Hooke, using a compound microscope, was the first to observe and describe cells in 1665. He observed the cell walls of cork and coined the term "cell" due to their resemblance to the small rooms in a monastery.

* Anton van Leeuwenhoek, using a single-lens microscope, observed living cells like bacteria and protozoa in the late 1600s.

Without the development of the compound microscope, the discovery of cells and the formulation of cell theory would have been impossible.

Therefore, while Janssen and Lippershey didn't directly contribute to cell theory itself, their invention of the compound microscope paved the way for its discovery and development.